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In chemistry and atomic physics, the main group is the group of elements (sometimes called the representative elements) whose lightest members are represented by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine as arranged in the periodic table of the elements. The main group includes the elements (except hydrogen ...
Therefore, it is located in group 1. Calcium (Ca) is in group 2, for it contains two valence electrons. In the old IUPAC system the letters A and B were designated to the left (A) and right (B) part of the table, while in the CAS system the letters A and B are designated to main group elements (A) and transition elements (B). The old IUPAC ...
The Roman numerals used correspond to the last digit of today's naming convention (e.g. the group 4 elements were group IVB, and the group 14 elements were group IVA). In Europe, the lettering was similar, except that "A" was used for groups 1 through 7, and "B" was used for groups 11 through 17. In addition, groups 8, 9 and 10 used to be ...
Most homoleptic organo-main group compounds adopt a characteristic oxidation state: RLi, R 2 Be, R 3 B/R 3 Al, R 4 Si, R 3 P, R 2 S. Members where the simplest stoichiometry violates the octet rule often aggregate by formation of bridging alkyl groups. When the alkyl group bridges two main group elements, the bonding is called three-center two ...
Element Negative states Positive states Group Notes −5 −4 −3 −2 −1 0 +1 +2 +3 +4 +5 +6 +7 +8 +9 Z; 1 hydrogen: H −1 +1: 1 2 helium: He 0 18
a Group 1 is composed of hydrogen (H) and the alkali metals. Elements of the group have one s-electron in the outer electron shell. Hydrogen is not considered to be an alkali metal as it is not a metal, though it is more analogous to them than any other group. This makes the group somewhat exceptional.
The 2005 IUPAC Red Book excludes hydrogen from the main-group elements, but this exclusion is often not followed in practice, and the 2011 IUPAC Principles of Chemical Nomenclature does not exclude hydrogen. The codification of those names is in the 2005 Red Book, when elements past Rg had not yet been approved.
Other pnictides include the ternary rare-earth (RE) main-group variety of pnictides. These are in the form of RE a M b Pn c, where M is a carbon group or boron group element and Pn is any pnictogen except nitrogen. These compounds are between ionic and covalent compounds and thus have unusual bonding properties.