query: where are noble gasses found on the periodic table

pos: Noble gas periods of the periodic table, the noble gases are exactly the members of group 18. Noble gases are typically highly unreactive except when under particular extreme conditions. The inertness of noble gases makes them very suitable in applications where reactions are not wanted. For example, argon is used in incandescent lamps to prevent the hot tungsten filament from oxidizing; also, helium is used in breathing gas by deep-sea divers to prevent oxygen, nitrogen and carbon dioxide (hypercapnia) toxicity. The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons

pos: Periodic table Periodic table The periodic table, or periodic table of elements, is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties, whose structure shows "periodic trends". Generally, within one row (period) the elements are metals to the left, and non-metals to the right, with the elements having similar chemical behaviours placed in the same column. Table rows are commonly called periods and columns are called groups. Six groups have accepted names as well as assigned numbers: for example, group 17 elements are the halogens; and group 18 are the noble gases. Also

pos: Block (periodic table) column of the periodic table, also known as group 0 or group 18. Noble gases are also called as aerogens but this nomenclature of the group is not officially accepted by the IUPAC. All of the noble gases have full outer shells with eight electrons. However, at the top of the noble gases is helium, with a shell that is full with only two electrons. The fact that their outer shells are full means they rarely react with other elements, which led to their original title of "inert". Because of their chemical properties, these gases are also used in the

pos: Period (periodic table) across periods. Seven periods of elements occur naturally on Earth. For period 8, which includes elements which may be synthesized after 2016, see the extended periodic table. A group in chemistry means a family of objects with similarities like different families. There are 7 periods, going horizontally across the periodic table. The first period contains the least elements than any other, with only two, hydrogen and helium. They therefore do not follow the octet rule. Chemically, helium behaves like a noble gas, and thus is taken to be part of the group 18 elements. However, in terms of its nuclear

pos: Noble gas compound Noble gas compound Noble gas compounds are chemical compounds that include an element from the noble gases, group 18 of the periodic table. Although the noble gases are generally unreactive elements, many such compounds have been observed, particularly involving the element xenon. From the standpoint of chemistry, the noble gases may be divided into two groups: the relatively reactive krypton (ionisation energy 14.0 eV), xenon (12.1 eV), and radon (10.7 eV) on one side, and the very unreactive argon (15.8 eV), neon (21.6 eV), and helium (24.6 eV) on the other. Consistent with this classification, Kr, Xe, and Rn form

pos: Noble gas compound of Ar, Kr, and Xe. (For instance, radioactive isotopes of krypton and xenon are difficult to store and dispose, and compounds of these elements may be more easily handled than the gaseous forms.) In addition, clathrates of radioisotopes may provide suitable formulations for experiments requiring sources of particular types of radiation; hence. Kr clathrate provides a safe source of beta particles, while Xe clathrate provides a useful source of gamma rays. Noble gas compound Noble gas compounds are chemical compounds that include an element from the noble gases, group 18 of the periodic table. Although the noble gases are generally

pos: Periodic table 13. The relatively inert noble gases, in group 18, bridge the most reactive groups of elements in the periodic table—the halogens in group 17 and the alkali metals in group 1. In 1789, Antoine Lavoisier published a list of 33 chemical elements, grouping them into gases, metals, nonmetals, and earths. Chemists spent the following century searching for a more precise classification scheme. In 1829, Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads based on their chemical properties. Lithium, sodium, and potassium, for example, were grouped together in a triad as soft, reactive metals. Döbereiner

pos: Periodic table outside of the context of electron configurations: When the noble gases (then called "inert gases") were first discovered around 1900, they were known as "group 0", reflecting no chemical reactivity of these elements known at that point, and helium was placed on the top of that group, as it did share the extreme chemical inertness seen throughout the group. As the group changed its formal number, many authors continued to assign helium directly above neon, in group 18; one of the examples of such placing is the current IUPAC table. Hydrogen's chemical properties are not very close to those of

pos: Period 1 element does not apply here. In terms of vertical trends down groups, helium can be seen as a typical noble gas at the head of Group 18, but as discussed below, hydrogen's chemistry is unique and it is not easily assigned to any group. Although both hydrogen and helium are in the s-block, neither of them behaves similarly to other s-block elements. Their behaviour is so different from the other s-block elements that there is considerable disagreement over where these two elements should be placed in the periodic table. Hydrogen is sometimes placed above lithium, above carbon, above fluorine, above both

pos: Group (periodic table) Group (periodic table) In chemistry, a group (also known as a family) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table, and the f-block columns (between groups 3 and 4) are not numbered. The elements in a group have similar physical or chemical characteristics of the outermost electron shells of their atoms (i.e., the same core charge), as most chemical properties are dominated by the orbital location of the outermost electron. There are three systems of group numbering. The modern numbering "group 1" to "group 18" is

pos: Electron affinity more positive "E" than metals. Atoms whose anions are more stable than neutral atoms have a greater "E". Chlorine most strongly attracts extra electrons; mercury most weakly attracts an extra electron. The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values. "E" generally increases across a period (row) in the periodic table prior to reaching group 18. This is caused by the filling of the valence shell of the atom; a group 17 atom releases more energy than a group 1 atom on gaining an electron because it

neg: Chemistry: A Volatile History for stranger). All the elements of this new group had one overwhelming characteristic; their lack of reactivity. It was this particular characteristic that brought to mind a name for the new group: the noble gases. Mendeleev's periodic table had brought order to all the elements, allowing him to make predictions that future scientists tested and found to be true. By the time he died he was world-renowned in chemistry. His periodic table was set in stone in St Petersburg and an element was eventually named after him: mendelevium. The periodic table does not however tell us why some elements are

neg: Periodic table in its closed electron shell, helium has only two electrons in the outermost electron orbital, while the rest of the noble gases have eight. Although scandium and yttrium are always the first two elements in group 3, the identity of the next two elements is not completely settled. They are commonly lanthanum and actinium, and less often lutetium and lawrencium. The two variants originate from historical difficulties in placing the lanthanides in the periodic table, and arguments as to where the "f" block elements start and end. It has been claimed that such arguments are proof that, "it is a

neg: Charge number that are positive are called cations. Charges that are negative are called anions. Elements in the same group have the same charge. A group in the periodic table is a term used to represent the vertical columns. The noble gases of the periodic table do not have a charge because they are nonreactive. Noble gases are considered stable since they contain the desired eight electrons. The other atoms or ions have charges because they are very reactive and want to react with another atom or ion to become stable. When elements are bonded, they can either be bonded by ionic

neg: Henry D. Hubbard Henry D. Hubbard Henry D. Hubbard was a member of the U.S. Bureau of Standards in the 1920s. He modernized Mendeleev's periodic table and in 1924 he produced a Periodic Table of Elements (called the Periodic Chart of the Atoms) which was distributed to schools and universities. This version of the periodic table placed the main groups in columns with some later groups taking up two rows per period and the Group VIIIB transition metals displayed out to the right of the noble gases. The noble gases themselves were shown first in Column 1 (Valence 0) and repeated in Column

neg: Periodic table intervals) and the formulation of the first periodic tables. Atomic radii vary in a predictable and explainable manner across the periodic table. For instance, the radii generally decrease along each period of the table, from the alkali metals to the noble gases; and increase down each group. The radius increases sharply between the noble gas at the end of each period and the alkali metal at the beginning of the next period. These trends of the atomic radii (and of various other chemical and physical properties of the elements) can be explained by the electron shell theory of the atom;

neg: Block (periodic table) the s-block, with its outer (and only) electrons in the 1s atomic orbital, although its chemical properties are more similar to the p-block noble gases due to its full shell. In addition to the blocks listed in this table, there is a hypothetical g-block which is not pictured here. The g-block elements can be seen in the expanded extended periodic table. Lanthanum and actinium are placed under scandium and yttrium to reflect their status as d-block elements, as they have no electrons in the 4f and 5f orbitals, respectively, while lutetium and lawrencium do. The s-block is on the left

neg: Periodic table a nonmetallic noble gas yet has some cationic chemistry that is characteristic of metals. Other classification schemes are possible such as the division of the elements into mineralogical occurrence categories, or crystalline structures. Categorizing the elements in this fashion dates back to at least 1869 when Hinrichs wrote that simple boundary lines could be placed on the periodic table to show elements having shared properties, such as metals, nonmetals, or gaseous elements. The electron configuration or organisation of electrons orbiting neutral atoms shows a recurring pattern or periodicity. The electrons occupy a series of electron shells (numbered 1, 2, and

neg: Periodic table element 172, rather than element 168, that emerges as the next noble gas after oganesson, although these must be regarded as speculative as no complete calculations have been done beyond element 122. The number of possible elements is not known. A very early suggestion made by Elliot Adams in 1911, and based on the arrangement of elements in each horizontal periodic table row, was that elements of atomic weight greater than circa 256 (which would equate to between elements 99 and 100 in modern-day terms) did not exist. A higher—more recent—estimate is that the periodic table may end soon after

neg: History of chemistry many of his predictions within his lifetime brought fame to Mendeleev as the founder of the periodic law. This organization surpassed earlier attempts at classification by Alexandre-Émile Béguyer de Chancourtois, who published the telluric helix, an early, three-dimensional version of the periodic table of the elements in 1862, John Newlands, who proposed the law of octaves (a precursor to the periodic law) in 1864, and Lothar Meyer, who developed an early version of the periodic table with 28 elements organized by valence in 1864. Mendeleev's table did not include any of the noble gases, however, which had not yet been

neg: Period (periodic table) eighth period. Period (periodic table) A period in the periodic table is a horizontal row. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor. Arranged this way, groups of elements in the same column have similar chemical and physical properties, reflecting the periodic law. For example, the alkali metals lie in the first column (group 1) and share similar properties, such as high reactivity and the tendency to lose one electron to arrive at a noble-gas electronic configuration. As of

neg: Period (periodic table) Period (periodic table) A period in the periodic table is a horizontal row. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor. Arranged this way, groups of elements in the same column have similar chemical and physical properties, reflecting the periodic law. For example, the alkali metals lie in the first column (group 1) and share similar properties, such as high reactivity and the tendency to lose one electron to arrive at a noble-gas electronic configuration. As of 2016, a

neg: Block (periodic table) form compounds. The first period elements in this block, however, are nonmetals. Hydrogen is highly chemically reactive, like the other s-block elements, but helium is a virtually unreactive noble gas. S-block elements are unified by the fact that their valence electrons (outermost electrons) are in the s orbital. The s-orbital is a single spherical cloud which can contain only one pair of electrons; hence, the s-block consists of only two columns in the periodic table. Elements in column 1, with a single s-orbital valence electron, are the most reactive of the block. Elements in the second column have two s-orbital

neg: Noble metal are covered by carbon monoxide very quickly. Metallic elements, including metalloids (metals usually considered noble bolded, predictions for superheavy elements italicised): The columns "group" and "period" denote its position in the periodic table, hence electronic configuration. The simplified "reaction"s, listed in the next column, can also be read in detail from the Pourbaix diagrams of the considered element in water. Finally the column "potential" indicates the electric potential of the element measured against a Standard hydrogen electrode. All missing elements in this table are either not metals or have a negative standard potential. Arsenic, antimony and tellurium are considered to

neg: Platinum group platinum group metals—ruthenium, rhodium and palladium—are formed as fission products in nuclear reactors. With escalating prices and increasing global demand, reactor-produced noble metals are emerging as an alternative source. Various reports are available on the possibility of recovering fission noble metals from spent nuclear fuel. Platinum group The platinum-group metals (abbreviated as the PGMs; alternatively, the platinoids, platinides, platidises, platinum group, platinum metals, platinum family or platinum-group elements (PGEs)) are six noble, precious metallic elements clustered together in the periodic table. These elements are all transition metals in the d-block (groups 8, 9, and 10, periods 5 and 6). The

neg: Argon showing that the periodic table is actually arranged in order of atomic number (see History of the periodic table). Argon's complete octet of electrons indicates full s and p subshells. This full valence shell makes argon very stable and extremely resistant to bonding with other elements. Before 1962, argon and the other noble gases were considered to be chemically inert and unable to form compounds; however, compounds of the heavier noble gases have since been synthesized. The first argon compound with tungsten pentacarbonyl, W(CO)Ar, was isolated in 1975. However it was not widely recognised at that time. In August 2000,

neg: Molecular mass also differs subtly from the molecular mass in that the choice of isotopes is defined and thus is a single specific molecular mass of the many possible. The masses used to compute the monoisotopic molecular mass are found on a table of isotopic masses and are not found on a typical periodic table. The average molecular mass is often used for larger molecules since molecules with many atoms are unlikely to be composed exclusively of the most abundant isotope of each element. A theoretical average molecular mass can be calculated using the standard atomic weights found on a typical periodic

neg: Unbinilium noble metals. The Δ"H" and −Δ"H" values are correlated for the alkaline earth metals. Unbinilium Unbinilium, also known as eka-radium or simply element 120, is the hypothetical chemical element in the periodic table with symbol Ubn and atomic number 120. "Unbinilium" and "Ubn" are the temporary systematic IUPAC name and symbol, until a permanent name is decided upon. In the periodic table of the elements, it is expected to be an s-block element, an alkaline earth metal, and the second element in the eighth period. It has attracted attention because of some predictions that it may be in the island

neg: Periodic table include a two-element s-block for elements 119 and 120, a new g-block for the next 18 elements, and 30 additional elements continuing the current f-, d-, and p-blocks, culminating in element 168, the next noble gas. More recently, physicists such as Pekka Pyykkö have theorized that these additional elements do not follow the Madelung rule, which predicts how electron shells are filled and thus affects the appearance of the present periodic table. There are currently several competing theoretical models for the placement of the elements of atomic number less than or equal to 172. In all of these it is

neg: Periodic table to 2B in American group numbering) and contains all of the transition metals. The f-block, often offset below the rest of the periodic table, has no group numbers and comprises lanthanides and actinides. According to their shared physical and chemical properties, the elements can be classified into the major categories of metals, metalloids and nonmetals. Metals are generally shiny, highly conducting solids that form alloys with one another and salt-like ionic compounds with nonmetals (other than noble gases). A majority of nonmetals are coloured or colourless insulating gases; nonmetals that form compounds with other nonmetals feature covalent bonding. In between

neg: Charge number that case, the charge of an ion could be written as formula_5. The charge number in chemistry normally relates to an electric charge. This is a property of specific subatomic atoms. These elements define the electromagnetic contact between the two elements. A chemical charge can be found by using the periodic table. An element's placement on the periodic table indicates whether its chemical charge is negative or positive. Looking at the table, one can see that the positive charges are on the left side of the table and the negative charges are on the right side of the table. Charges

neg: Properties of metals, metalloids and nonmetals Most are gases at room temperature; have relatively low densities; are poor electrical and thermal conductors; have relatively high ionisation energies and electronegativities; form acidic oxides; and are found naturally in uncombined states in large amounts. Some nonmetals (C, black P, S and Se) are brittle solids at room temperature (although each of these also have malleable, pliable or ductile allotropes). From left to right in the periodic table, the nonmetals can be subdivided into the reactive nonmetals which, being nearest to the metalloids, show some incipient metallic character, and the monatomic noble gases, which are almost completely inert. properties

neg: Periodic table The other elements may behave differently from what would be predicted by extrapolation, due to relativistic effects; for example, flerovium has been predicted to possibly exhibit some noble-gas-like properties, even though it is currently placed in the carbon group. The current experimental evidence still leaves open the question of whether flerovium behaves more like a metal or a noble gas. It is unclear whether new elements will continue the pattern of the current periodic table as period 8, or require further adaptations or adjustments. Seaborg expected the eighth period to follow the previously established pattern exactly, so that it would

neg: Periodic Videos water) and sulfuric acid. Also filmed are "Chem definitions" that provide an explanation to words that are used in chemistry. Lastly, the team has filmed "Roadtrips" where they travel to different places in the world that have an importance in chemistry (such as the mine outside Ytterby, Sweden, which had four elements – yttrium, terbium, erbium, and ytterbium – named after it.) Periodic Videos The Periodic Table of Videos (usually shortened to Periodic Videos) is a series of videos about chemical elements and the periodic table. They are published on YouTube and produced by Brady Haran, a former BBC video

neg: Periodic table structure explain group trends by proposing that elements within the same group generally have the same electron configurations in their valence shell. Consequently, elements in the same group tend to have a shared chemistry and exhibit a clear trend in properties with increasing atomic number. In some parts of the periodic table, such as the d-block and the f-block, horizontal similarities can be as important as, or more pronounced than, vertical similarities. Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases).

neg: History of the periodic table (Z=19), despite the fact that argon's atomic weight of 39.9 is greater than the atomic weight of potassium (39.1). The new order was in agreement with the chemical properties of these elements, since argon is a noble gas and potassium is an alkali metal. Similarly, Moseley placed cobalt before nickel and was able to explain that tellurium occurs before iodine, without revising the experimental atomic weight of tellurium, as had been proposed by Mendeleev. Moseley's research showed that there were gaps in the periodic table at atomic numbers 43 and 61, which are now known to be occupied by technetium

neg: Bohr model approximately by measuring the viscosity of gases and density of pure crystalline solids. Atoms tend to get smaller toward the right in the periodic table, and become much larger at the next line of the table. Atoms to the right of the table tend to gain electrons, while atoms to the left tend to lose them. Every element on the last column of the table is chemically inert (noble gas). In the shell model, this phenomenon is explained by shell-filling. Successive atoms become smaller because they are filling orbits of the same size, until the orbit is full, at which

neg: Nonmetal nonmetals tend to form predominately covalent compounds with metals. Six nonmetals are categorised as noble gases: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn). In periodic table terms they occupy the outermost right column. They are called "noble gases" in light of their characteristically very low chemical reactivity. They have very similar properties, all being colorless, odorless, and nonflammable. With their closed valence shells the noble gases have feeble interatomic forces of attraction resulting in very low melting and boiling points. That is why they are all gases under standard conditions, even those

neg: Period 4 element such, krypton is often used in fluorescent lights. Krypton, like most noble gases, is also used in lighting because of its many spectral lines and the aforementioned reasons. Period 4 element A period 4 element is one of the chemical elements in the fourth row (or "period") of the periodic table of the elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same

neg: History of the periodic table managed to get thallium, lead, mercury and platinum into the right groups, which is something that Mendeleev failed to do at his first attempt. Odling failed to achieve recognition, however, since it is suspected that he, as Secretary of the Chemical Society of London, was instrumental in discrediting Newlands' earlier work on the periodic table. By 1912 almost 50 different radioactive elements had been found, too many for the periodic table. Frederick Soddy in 1913 found that although they emitted different radiation, many elements were alike in their chemical characteristics so shared the same place on the table. They became

neg: Noble gas these interactions became tractable because the noble gases are monatomic and the atoms spherical, which means that the interaction between the atoms is independent of direction, or isotropic. The noble gases are colorless, odorless, tasteless, and nonflammable under standard conditions. They were once labeled "group 0" in the periodic table because it was believed they had a valence of zero, meaning their atoms cannot combine with those of other elements to form compounds. However, it was later discovered some do indeed form compounds, causing this label to fall into disuse. Like other groups, the members of this family show patterns

neg: Extended periodic table are bound so strongly that they are no longer active chemically, so that only a few electrons can participate in chemical reactions. Calculations by Fricke et al. predict that at element 154, the 6f shell is full and there are no d- or other electron wave functions outside the chemically inactive 8s and 8p shells. This would cause element 154 to be very unreactive, so that it may exhibit properties similar to those of the noble gases. Similarly to the lanthanide and actinide contractions, there should be a superactinide contraction in the superactinide series where the ionic radii of the

neg: Argon Earth and with interplanetary gasses, measured by probes. The atmospheres of Mars, Mercury and Titan (the largest moon of Saturn) contain argon, predominantly as , and its content may be as high as 1.93% (Mars). The predominance of radiogenic is the reason the standard atomic weight of terrestrial argon is greater than that of the next element, potassium, a fact that was puzzling when argon was discovered. Mendeleev positioned the elements on his periodic table in order of atomic weight, but the inertness of argon suggested a placement "before" the reactive alkali metal. Henry Moseley later solved this problem by

neg: Period 2 element inert. It is one of the so-called "noble gases". Neon is a trace component of the atmosphere without any biological role. Period 2 element A period 2 element is one of the chemical elements in the second row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases; a new row is started when chemical behavior begins to repeat, creating columns of elements with similar properties. The second period contains the elements lithium, beryllium, boron,

neg: Periodic table the almost completely inert, monatomic noble gases. Specialized groupings such as refractory metals and noble metals, are examples of subsets of transition metals, also known and occasionally denoted. Placing elements into categories and subcategories based just on shared properties is imperfect. There is a large disparity of properties within each category with notable overlaps at the boundaries, as is the case with most classification schemes. Beryllium, for example, is classified as an alkaline earth metal although its amphoteric chemistry and tendency to mostly form covalent compounds are both attributes of a chemically weak or post-transition metal. Radon is classified as

neg: Post-transition metal nonmetals (that is, the noble gases). The "metametals" are zinc, cadmium, mercury, indium, thallium, tin and lead. They are ductile elements but, compared to their metallic periodic table neighbours to the left, have lower melting points, relatively low electrical and thermal conductivities, and show distortions from close-packed forms. Sometimes beryllium and gallium are included as metametals despite having low ductility. Abrikosov distinguishes between "ordinary metals", and transition metals where the inner shells are not filled. The ordinary metals have lower melting points and cohesive energies than those of the transition metals. Gray identifies as ordinary metals: aluminium, gallium, indium, thallium,

neg: Period 1 element (He) is a colorless, odorless, tasteless, non-toxic, inert monatomic chemical element that heads the noble gas series in the periodic table and whose atomic number is 2. Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions. Helium was discovered in 1868 by French astronomer Pierre Janssen, who first detected the substance as an unknown yellow spectral line signature in light from a solar eclipse. In 1903, large reserves of helium were found in the natural gas fields of the United States, which is by far the largest

neg: Periodic table three naturally occurring isotopes: all of its atoms have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons. Isotopes are never separated in the periodic table; they are always grouped together under a single element. Elements with no stable isotopes have the atomic masses of their most stable isotopes, where such masses are shown, listed in parentheses. In the standard periodic table, the elements are listed in order of increasing atomic number "Z" (the number of protons in the nucleus of an atom). A

neg: Periodic trends force. Metals are ductile while nonmetals are not. Periodic trends Periodic trends are specific patterns in the properties of chemical elements that are revealed in the periodic table of elements. Major periodic trends include electronegativity, ionization energy, electron affinity, atomic radius, ionic radius, metallic character, and chemical reactivity. Periodic trends arise from the changes in the atomic structure of the chemical elements within their respective periods (horizontal rows) and groups in the periodic table. These trends enable the chemical elements to be organized in the periodic table based on their atomic structures and properties. Some exceptions to these trends exist,

neg: Nonmetal as nonmetals. Among the reactive nonmetals, carbon, phosphorus, selenium, and iodine—which border the metalloids—show some metallic character, as does hydrogen. Among the noble gases, radon is the most metallic and begins to show some cationic behaviour, which is unusual for a nonmetal. The seven metalloids are boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), and astatine (At). On a standard periodic table, they occupy a diagonal area in the p-block extending from boron at the upper left to astatine at lower right, along the dividing line between metals and nonmetals shown on some periodic tables. They

neg: Homology (chemistry) Homology (chemistry) In chemistry, homology is the appearance of homologues. A homologue (also spelled as homolog) is a compound belonging to a series of compounds differing from each other by a repeating unit, such as a methylene bridge −−, a peptide residue, etc. A homolog is a special case of an analog. Examples are alkanes and compounds with alkyl side chains of different length (the repeating unit being a methylene group -CH-). On the periodic table, homologous elements share many electrochemical properties and appear in the same group (column) of the table. For example, all noble gases are colorless, monatomic

neg: Periodic table been slowly expanded and refined with the discovery or synthesis of further new elements and the development of new theoretical models to explain chemical behaviour. The modern periodic table now provides a useful framework for analyzing chemical reactions, and continues to be widely used in chemistry, nuclear physics and other sciences. All the elements from atomic numbers 1 (hydrogen) through 118 (oganesson) have been either discovered or synthesized, completing the first seven rows of the periodic table. The first 98 elements exist in nature, although some are found only in trace amounts and others were synthesized in laboratories before being

neg: Extended periodic table 8p electrons are bound so strongly in these elements that they should not be able to take part in any chemical reactions, the 9s and 9p levels are expected to be readily available for hybridization. The noble metals of this series of transition metals are not expected to be as noble as their lighter homologues, due to the absence of an outer "s" shell for shielding and also because the 7d shell is strongly split into two subshells due to relativistic effects. This causes the first ionization energies of the 7d transition metals to be smaller than those of their

neg: Block (periodic table) rare. It was once used for its semiconductor properties pretty much as silicon is now, and it has some superior properties at that, but is now a rare material in the industry. Arsenic is a toxic metalloid that has been used throughout history as an additive to metal alloys, paints, and even makeup. Antimony is used as a constituent in casting alloys such as printing metal. Previously called inert gases, their name was changed as there are a few other gases that are inert but not noble gases, such as nitrogen. The noble gases are located in the far right

neg: Extended periodic table 121-138 form the g-block superactinides; 139-152 form the f-block superactinides, 153-161 would be transition metals; 162-166 post-transition metals; 167=halogen; 168=noble gas; 169=alkali metal; 170=alkaline earth metal, Dirac-Fock calculations predict that it will most likely go: 121-142 form the g-block superactinides; 143-156 form the f-block superactinides; 157-165 form the transition metals; 166-170 post-transition metals; 171=halogen; 172=noble gas. Not all models show the higher elements following the pattern established by lighter elements. Pekka Pyykkö, for example, used computer modeling to calculate the positions of elements up to "Z" = 172 and their possible chemical properties. He found that several elements were displaced

neg: Table of nuclides (segmented, narrow) Periodic table ← Previous | Next →Go to Periodic table ← Previous | Next →Go to Periodic table ← Previous | Next →Go to Periodic table ← Previous | Next →Go to Periodic table ← Previous | Next →Go to Periodic table ← Previous | Next →Go to Periodic table Table of nuclides (segmented, narrow) These isotope tables show all of the known isotopes of the chemical elements, arranged with increasing atomic number from left to right and increasing neutron number from top to bottom. Half lives are indicated by the color of each isotope's cell (see color chart in

neg: Periodic table of topological invariants Periodic table of topological invariants The periodic table of topological invariants is an application of topology to physics. It indicates the group of topological invariant for topological insulators and superconductors in each dimension and in each discrete symmetry class. There are ten discrete symmetry classes of topological insulators and superconductors, corresponding to the ten Altland–Zirnbauer classes of random matrices. They are defined by three symmetries of the Hamiltonian formula_1, (where formula_2, and formula_3, are the annihilation and creation operators of mode formula_4, in some arbitrary spatial basis) : time reversal symmetry, particle hole (or charge conjugation) symmetry, and chiral (or

neg: Periodic trends Periodic trends Periodic trends are specific patterns in the properties of chemical elements that are revealed in the periodic table of elements. Major periodic trends include electronegativity, ionization energy, electron affinity, atomic radius, ionic radius, metallic character, and chemical reactivity. Periodic trends arise from the changes in the atomic structure of the chemical elements within their respective periods (horizontal rows) and groups in the periodic table. These trends enable the chemical elements to be organized in the periodic table based on their atomic structures and properties. Some exceptions to these trends exist, such as that of ionization energy in Groups

neg: Periodic table 11, electronegativity increases farther down the group. A "period" is a horizontal row in the periodic table. Although groups generally have more significant periodic trends, there are regions where horizontal trends are more significant than vertical group trends, such as the f-block, where the lanthanides and actinides form two substantial horizontal series of elements. Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and electronegativity. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron, which causes the electron to be drawn

neg: Group (periodic table) names to mean different things. The new system simply numbers the groups increasingly from left to right on the standard periodic table. The IUPAC proposal was first circulated in 1985 for public comments, and was later included as part of the 1990 edition of the "Nomenclature of Inorganic Chemistry". Group (periodic table) In chemistry, a group (also known as a family) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table, and the f-block columns (between groups 3 and 4) are not numbered. The elements in a group

neg: Properties of metals, metalloids and nonmetals are brittle (e.g. Os, Bi), not easily machined (e.g. Ti, Re), or are noble (hard to oxidise) or have nonmetallic structures (Mn and Ga are structurally analogous to, respectively, white P and I). Metals comprise the large majority of the elements, and can be subdivided into several different categories. From left to right in the periodic table, these categories include the highly reactive alkali metals; the less reactive alkaline earth metals, lanthanides and radioactive actinides; the archetypal transition metals, and the physically and chemically weak post-transition metals. Specialized subcategories such as the refractory metals and the noble metals also exist.

neg: Charles Janet series to element 120. Janet's table differs from the standard table in placing the s-block elements on the right, so that the subshells of the periodic table are arranged in the order (n-3)s, (n-2)p, (n-1)d, nf from left to right. There is then no need to interrupt the sequence or move the f block into a 'footnote'. He believed that no elements heavier than number 120 would be found, so he did not envisage a g block. In terms of atomic quantum numbers, each row corresponds to one value of the sum where n is the principal quantum number and

neg: Atomic radii of the elements (data page) on the atom's state and context. Atomic radii vary in a predictable and explicable manner across the periodic table. For instance, the radii generally decrease rightward along each period (row) of the table, from the alkali metals to the noble gases; and increase down each group (column). The radius increases sharply between the noble gas at the end of each period and the alkali metal at the beginning of the next period. These trends of the atomic radii (and of various other chemical and physical properties of the elements) can be explained by the electron shell theory of the atom;

neg: History of the periodic table History of the periodic table The periodic table is an arrangement of the chemical elements and are organized on the basis of their atomic numbers, electron configurations and recurring chemical properties. Elements are presented in order of increasing atomic number. The standard form of the table consists of a grid of elements with rows called periods and columns called groups. The history of the periodic table reflects over a century of growth in the understanding of chemical properties. The most important event in its history occurred in 1869, when the table was published by Dmitri Mendeleev, who built upon earlier

neg: Periodic table centre and the transition metals, lanthanides, and actinides occupying peninsulas. Most periodic tables are two-dimensional; three-dimensional tables are known to as far back as at least 1862 (pre-dating Mendeleev's two-dimensional table of 1869). More recent examples include Courtines' Periodic Classification (1925), Wringley's Lamina System (1949), Giguère's Periodic helix (1965) and Dufour's Periodic Tree (1996). Going one further, Stowe's Physicist's Periodic Table (1989) has been described as being four-dimensional (having three spatial dimensions and one colour dimension). The various forms of periodic tables can be thought of as lying on a chemistry–physics continuum. Towards the chemistry end of the continuum can

neg: Periodic table found to be correct and he subsequently went on to win the 1951 Nobel Prize in chemistry for his work in synthesizing actinide elements. Although minute quantities of some transuranic elements occur naturally, they were all first discovered in laboratories. Their production has expanded the periodic table significantly, the first of these being neptunium, synthesized in 1939. Because many of the transuranic elements are highly unstable and decay quickly, they are challenging to detect and characterize when produced. There have been controversies concerning the acceptance of competing discovery claims for some elements, requiring independent review to determine which party has

neg: Periodic table be found, as an example, Rayner-Canham's "unruly" Inorganic Chemist's Periodic Table (2002), which emphasizes trends and patterns, and unusual chemical relationships and properties. Near the physics end of the continuum is Janet's Left-Step Periodic Table (1928). This has a structure that shows a closer connection to the order of electron-shell filling and, by association, quantum mechanics. A somewhat similar approach has been taken by Alper, albeit criticized by Eric Scerri as disregarding the need to display chemical and physical periodicity. Somewhere in the middle of the continuum is the ubiquitous common or standard form of periodic table. This is regarded

neg: Periodic table of the nucleus by d and f electrons, and relativistic effects, tends to increase going down a group (or column or family). Thus, the most metallic elements (such as caesium and francium) are found at the bottom left of traditional periodic tables and the most nonmetallic elements (oxygen, fluorine, chlorine) at the top right. The combination of horizontal and vertical trends in metallic character explains the stair-shaped dividing line between metals and nonmetals found on some periodic tables, and the practice of sometimes categorizing several elements adjacent to that line, or elements adjacent to those elements, as metalloids. From left

neg: The Periodic Table (Basher book) different group of the periodic table (hydrogen, the alkali metals, the alkaline earth metals, the transition metals, the boron elements, the carbon elements, the nitrogen elements, the oxygen elements, the halogen elements, the noble gases, the lanthanides and actinides, and the transactinides). For every type of then known atom, Basher has created a "manga-esque" cartoon, and for many types of atoms, Dingle, a high-school chemistry teacher who also developed an award-winning chemistry website has written a couple paragraphs of facts to go with the cartoon. Dingle, who says that "[s]cience is a serious business", wanted in writing the book "to

neg: Periodic table with the degree of ionization. For magnesium as an example, the first ionization energy is 738 kJ/mol and the second is 1450 kJ/mol. Electrons in the closer orbitals experience greater forces of electrostatic attraction; thus, their removal requires increasingly more energy. Ionization energy becomes greater up and to the right of the periodic table. Large jumps in the successive molar ionization energies occur when removing an electron from a noble gas (complete electron shell) configuration. For magnesium again, the first two molar ionization energies of magnesium given above correspond to removing the two 3s electrons, and the third ionization energy

neg: Period 1 element lithium and fluorine (appearing twice), or left floating above the other elements and not assigned to any group in the periodic table. Helium is almost always placed above neon (which is in the p-block) in the periodic table as a noble gas, although it is occasionally placed above beryllium due to their similar electron configuration. Hydrogen (H) is the chemical element with atomic number 1. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H. With an atomic mass of 1.00794 amu, hydrogen is the lightest element. Hydrogen is

neg: Extended periodic table due to its much higher atomic weight. Unseptbium should be a strong Lewis acid, forming fluorides and oxides, similarly to its lighter congener xenon. Because of this analogy of elements 165–172 to periods 2 and 3, Fricke et al. considered them to form a ninth period of the periodic table, while the eighth period was taken by them to end at the noble metal element 164. This ninth and final period would be similar to the second and third period in that it should have no transition metals. Immediately after element 172 (unseptbium, the last period 8 element), the first

neg: Atomic radius and the size and shape of molecules. Atomic radii vary in a predictable and explicable manner across the periodic table. For instance, the radii generally decrease along each period (row) of the table, from the alkali metals to the noble gases; and increase down each group (column). The radius increases sharply between the noble gas at the end of each period and the alkali metal at the beginning of the next period. These trends of the atomic radii (and of various other chemical and physical properties of the elements) can be explained by the electron shell theory of the atom;

neg: TriQuint Semiconductor to the gallium arsenide on which the company was founded. *Tri, from the Greek for “a prefix meaning three, thrice, threefold”, and quint, from the Latin for “a set or sequence of five” literally means 3-5. 3-5 refers to the location of the elements gallium and arsenic on the periodic table. The elements on the third and fifth columns of the periodic table, including nitrogen found in GaN, are known to have special conductive properties, great for producing compound semiconductors. Alan Patz was the first chief executive officer (CEO) of the company, serving from 1985 until 1991. In 1988, the

neg: Periodic boundary conditions to smooth real functions formula_1 by for all m = 0, 1, 2, ... and for constants formula_6 and formula_7. In molecular dynamics simulation, PBC are usually applied to calculate bulk gasses, liquids, crystals or mixtures. A common application uses PBC to simulate solvated macromolecules in a bath of explicit solvent. Born-von Karman boundary conditions are periodic boundary conditions for a special system. Three-dimensional PBCs are useful for approximating the behavior of macro-scale systems of gases, liquids, and solids. Three-dimensional PBCs can also be used to simulate planar surfaces, in which case two-dimensional PBCs are often more suitable. Two-dimensional PBCs

neg: Nonmetal selenium and bromine, have unusually small atomic radii because the 3d electrons are not effective at shielding the increased nuclear charge, and smaller atomic size correlates with higher electronegativity. Immediately to the left of most nonmetals on the periodic table are "metalloids" such as boron, silicon, and germanium, which generally behave chemically like nonmetals, and are included here for comparative purposes. In this sense they can be regarded as the most metallic of nonmetallic elements. Based on shared attributes, the nonmetals can be divided into the two categories of "reactive nonmetal," and "noble gas." The metalloids and the two nonmetal

neg: Copernicium 12 element in the periodic table, below zinc, cadmium and mercury. It is predicted to differ significantly from the lighter group 12 elements. The valence s-subshells of the group 12 elements and period 7 elements are expected to be relativistically contracted most strongly at copernicium. This and the closed-shell configuration of copernicium result in it probably being a very noble metal. Its metallic bonds should also be very weak, possibly making it extremely volatile, like the noble gases, and potentially making it gaseous at room temperature. However, it should be able to form metal–metal bonds with copper, palladium, platinum, silver,

neg: Extended periodic table of the extended period had the heavier elements following the pattern set by lighter elements, as it did not take into account relativistic effects, models that take relativistic effects into account do not. Pekka Pyykkö and Burkhard Fricke used computer modeling to calculate the positions of elements up to "Z" = 172, and found that several were displaced from the Madelung rule. As a result of uncertainty and variability in predictions of chemical and physical properties of elements beyond 120, there is currently no consensus on their placement in the extended periodic table. Elements in this region are likely to

neg: Names for sets of chemical elements the name used is "category". Very often these categories are marked by a background color in the periodic table. Category names used here, without any claim to universality, are: Many other names for sets of elements are in common use, and yet others have been used throughout history. These sets usually do not aim to cover the whole periodic table (as for example "period" does). Some examples: Names for sets of chemical elements There are currently 118 known chemical elements exhibiting a large number of different physical and chemical properties. Amongst this diversity, scientists have found it useful to use

neg: Periodic table of the appearance of Mendeleev's table in 1869, Edward G. Mazurs had collected an estimated 700 different published versions of the periodic table. As well as numerous rectangular variations, other periodic table formats have been shaped, for example, like a circle, cube, cylinder, building, spiral, lemniscate, octagonal prism, pyramid, sphere, or triangle. Such alternatives are often developed to highlight or emphasize chemical or physical properties of the elements that are not as apparent in traditional periodic tables. A popular alternative structure is that of Otto Theodor Benfey (1960). The elements are arranged in a continuous spiral, with hydrogen at the

neg: Chromium chromium (Cr(III)) ion is considered an essential nutrient in humans for insulin, sugar and lipid metabolism. However, in 2014, the European Food Safety Authority, acting for the European Union, concluded that there was not sufficient evidence for chromium to be recognized as essential. While chromium metal and Cr(III) ions are not considered toxic, hexavalent chromium (Cr(VI)) is both toxic and carcinogenic. Abandoned chromium production sites often require environmental cleanup. Chromium is the fourth transition metal found on the periodic table, and has an electron configuration of [Ar] 3d 4s. It is also the first element in the periodic table whose

neg: Ida Freund Periodic Table with a set of periodic table cupcakes and students at Nottingham University did similarly for the birthday of Martyn Poliakoff. A video showing the collection of cakes is included in Professor Poliakoff's series of online videos 'Periodic Videos' Periodic Videos aim to bring chemistry to a new generation of students. Recipe instructions for modern versions of Freund's periodic table of cupcakes are available from a variety of sources online. As well as inventing periodic table cupcakes, Freund also had a piece of laboratory apparatus (a gas measuring tube) named after her as her invention. The apparatus is no

neg: Diagonal relationship Diagonal relationship A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods (first 20 elements) of the periodic table. These pairs (lithium (Li) and magnesium (Mg), beryllium (Be) and aluminium (Al), boron (B) and silicon (Si) "etc".) exhibit similar properties; for example, boron and silicon are both semiconductors, forming halides that are hydrolysed in water and have acidic oxides. The organization of elements on the periodic table in to horizontal rows and vertical columns makes certain relationships more apparent (periodic law). Moving rightward and descending the periodic table have opposite

neg: Alternative periodic tables extended periodic table, suggested by Glenn T. Seaborg in 1969, yet unknown elements are included up to atomic number 218. Theoretical periods above regular period 7 are added. In the research field of superatoms, clusters of atoms have properties of single atoms of another element. It is suggested to extend the periodic table with a second layer to be occupied with these cluster compounds. The latest addition to this multi-story table is the aluminium cluster ion , which behaves like a multivalent germanium atom. Alternative periodic tables Alternative periodic tables are tabulations of chemical elements differing significantly in their organization

neg: Extended periodic table be unbound and undergo proton emission. Cluster decay (heavy particle emission) has also been proposed as an alternative decay mode for some isotopes, posing yet another hurdle to identification of these elements. The following are the expected electron configurations of elements 118–173. Beyond element 122, no complete calculations are available and hence the data in this table must be taken as tentative. Extended periodic table An extended periodic table theorizes about chemical elements beyond those currently known and proven up through oganesson, which completes the seventh period (row) in the periodic table at atomic number ("Z") 118. If further elements

neg: Table of nuclides (combined) and isobars, see "Table of nuclides". ← Previous | Next →Go to Unitized table (all elements)Go to Periodic table ← Previous | Next →Go to Unitized table (all elements)Go to Periodic table ← Previous | Next →Go to Unitized table (all elements)Go to Periodic table ← Previous | Next →Go to Unitized table (all elements)Go to Periodic table ← Previous | Next →Go to Unitized table (all elements)Go to Periodic table ← Previous | Next →Go to Unitized table (all elements)Go to Periodic table ← Previous | Next →Go to Unitized table (all elements)Go to Periodic table ← Previous |

neg: Block (periodic table) in the extended periodic table whose outermost electrons are posited to include one or more g-orbital electrons. Block (periodic table) A block of the periodic table of elements is a set of adjacent groups. The term appears to have been first used by Charles Janet. The respective highest-energy electrons in each element in a block belong to the same atomic orbital type. Each block is named after its characteristic orbital; thus, the blocks are: The block names (s, p, d, f and g) are derived from the spectroscopic notation for the associated atomic orbitals: sharp, principal, diffuse and fundamental, and

neg: Extended periodic table Extended periodic table An extended periodic table theorizes about chemical elements beyond those currently known and proven up through oganesson, which completes the seventh period (row) in the periodic table at atomic number ("Z") 118. If further elements with higher atomic numbers than this are discovered, they will be placed in additional periods, laid out (as with the existing periods) to illustrate periodically recurring trends in the properties of the elements concerned. Any additional periods are expected to contain a larger number of elements than the seventh period, as they are calculated to have an additional so-called "g-block", containing at

neg: History of the periodic table published his periodic table of the known elements, predicted new elements to help complete his table and corrected the atomic weights of some of the elements, Meyer published a virtually identical periodic table. Meyer and Mendeleev are considered by some historians of science to be the co-creators of the periodic table, but Mendeleev's accurate prediction of the qualities of undiscovered elements enables him to have the larger share of the credit. In 1864, the English chemist William Odling also drew up a table that was remarkably similar to the table produced by Mendeleev. Odling overcame the tellurium-iodine problem and even

neg: Henry Moseley of a missing element in the Periodic Table, which was later found to be filled by technetium, and Bohuslav Brauner had predicted the existence of another missing element in this Table, which was later found to be filled by promethium. Henry Moseley's experiments confirmed these predictions, by showing exactly what the missing atomic numbers were, 43 and 61. In addition, Moseley predicted the existence of two more undiscovered elements, those with the atomic numbers 72 and 75, and gave very strong evidence that there were no other gaps in the Periodic Table between the elements aluminium (atomic number 13) and

neg: Extended periodic table (detailed cells) the seventh period, as they are calculated to have an additional so-called g-block, containing 18 elements with partially filled "g-orbitals" in each period. An eight-period table containing this block was suggested by Glenn T. Seaborg in 1969. It is not known how many elements are physically possible, if period 8 is complete, or if there is a period 9. Chemical series information for elements past hassium (except copernicium), is hypothetical and based on periodic trends. Superheavy elements may not exist, and may not follow the order of this table even if they do. Extended periodic table (detailed cells) This is

neg: Noble gas of argon was reported in 2000 when argon fluorohydride (HArF) was formed at a temperature of . In December 1998, scientists at the Joint Institute for Nuclear Research working in Dubna, Russia bombarded plutonium (Pu) with calcium (Ca) to produce a single atom of element 114, flerovium (Fl). Preliminary chemistry experiments have indicated this element may be the first superheavy element to show abnormal noble-gas-like properties, even though it is a member of group 14 on the periodic table. In October 2006, scientists from the Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory successfully created synthetically oganesson (Og),

neg: Extended periodic table periodic table would quite possibly end around "Z" = 130. Beyond element 164, the fissility line defining the limit of stability with respect to spontaneous fission may converge with the neutron drip line, posing a limit to the existence of heavier elements. Nevertheless, further magic numbers have been predicted at "Z" = 210, 274, and 354 and "N" = 308, 406, 524, 644, and 772, with two beta-stable doubly magic nuclei found at 210 and 274; the same calculation method reproduced the predictions for Fl and 164. Although additional stability toward alpha decay and fission are predicted for these nuclei,

neg: Chemically inert Chemically inert In chemistry, the term chemically inert is used to describe a substance that is not chemically reactive. Most Group 8 or 18 elements that appear in the last column of the periodic table (Helium, Neon, Argon, Krypton, Xenon and Radon) are classified as inert (or unreactive). These elements are stable in their naturally occurring form (gaseous form) and they are called inert gases. The noble gases were previously known as "inert gases" because of their perceived lack of participation in any chemical reactions. The reason for this is that their outermost electron shells (valence shells) are completely filled,

neg: Periodic table of topological invariants dimensions can be labeled by the elements of the formula_46-th homotopy group of the symmetric space. These groups are displayed in this table, called the periodic table of topological insulators: There may also exist weak topological invariants (associated to the fact that the suspension of the Brillouin zone is in fact equivalent to a formula_66 sphere wedged with lower-dimensional spheres), which are not included in this table. Furthermore, the table assumes the limit of an infinite number of bands, i.e. involves formula_67 Hamiltonians for formula_68. The table also is periodic in the sense that the group of invariants in formula_46

neg: Periodic Videos Periodic Videos The Periodic Table of Videos (usually shortened to Periodic Videos) is a series of videos about chemical elements and the periodic table. They are published on YouTube and produced by Brady Haran, a former BBC video journalist, featuring Sir Martyn Poliakoff ("The Professor"), Peter Licence, Stephen Liddle, Debbie Kays, Neil Barnes, Sam Tang and others at the University of Nottingham. The project began recording on 9 June 2008 and the initial videos were completed on 17 July 2008. The collection includes videos, each just a few minutes long, for all 118 known elements with a video for each

neg: Moseley's law den Broek had made the bold suggestion that "Z" was not half of the atomic weight for elements, but instead was exactly equal to the element's atomic number, or place in the periodic table. This position in the table was not known to have any physical significance up to that time, except as a way to order elements in a particular sequence so that their chemical properties would match up. The ordering of atoms in the periodic table did tend to be according to atomic "weights", but there were a few famous "reversed" cases where the periodic table demanded that

neg: Metallic bonding K) being extremely high. A remarkable exception are the elements of the zinc group: Zn, Cd, and Hg. Their electron configuration ends in ...ns and this comes to resemble a noble gas configuration like that of helium more and more when going down in the periodic table because the energy distance to the empty np orbitals becomes larger. These metals are therefore relatively volatile, and are avoided in ultra-high vacuum systems. Otherwise, metallic bonding can be very strong, even in molten metals, such as Gallium. Even though gallium will melt from the heat of one's hand just above room temperature,

neg: Chemically inert gas is mainly used to fill hot air and party balloons. Balloons filled with it float upwards and this phenomenon is achieved as helium gas is less dense than air Chemically inert In chemistry, the term chemically inert is used to describe a substance that is not chemically reactive. Most Group 8 or 18 elements that appear in the last column of the periodic table (Helium, Neon, Argon, Krypton, Xenon and Radon) are classified as inert (or unreactive). These elements are stable in their naturally occurring form (gaseous form) and they are called inert gases. The noble gases were previously

neg: Geochemistry affinity for other elements and the type of bonds it forms – is determined by the arrangement of electrons in orbitals, particularly the outermost (valence) electrons. These arrangements are reflected in the position of elements in the periodic table. Based on position, the elements fall into the broad groups of alkali metals, alkaline earth metals, transition metals, semi-metals (also known as metalloids), halogens, noble gases, lanthanides and actinides. Another useful classification scheme for geochemistry is the Goldschmidt classification, which places the elements into four main groups. "Lithophiles" combine easily with oxygen. These elements, which include Na, K, Si, Al, Ti,