silicon (si) is in group 14.
what group is silicon (si) in?
14
tetrahedral coordination is a major structural motif in silicon chemistry just as it is for carbon chemistry. however, the 3p subshell is rather more diffuse than the 2p subshell and does not hybridise so well with the 3s subshell. as a result, the chemistry of silicon and its heavier congeners shows significant differences from that of carbon, and thus octahedral coordination is also significant. for example, the [[electronegativity]] of silicon (1.90) is much less than that of carbon (2.55), because the valence electrons of silicon are further from the nucleus than those of carbon and hence experience smaller electrostatic forces of attraction from the nucleus. the poor overlap of 3p orbitals also results in a much lower tendency toward [[catenation]] (formation of si–si bonds) for silicon than for carbon, due to the concomitant weakening of the si–si bond compared to the c–c bond: the average si–si bond energy is approximately 226 kj/mol, compared to a value of 356 kj/mol for the c–c bond. this results in multiply bonded silicon compounds generally being much less stable than their carbon counterparts, an example of the [[double bond rule]]. on the other hand, the presence of 3d orbitals in the valence shell of silicon suggests the possibility of [[hypervalence]], as seen in five and six-coordinate derivatives of silicon such as and . lastly, because of the increasing energy gap between the valence s and p orbitals as the group is descended, the divalent state grows in importance from carbon to lead, so that a few unstable divalent compounds are known for silicon; this lowering of the main oxidation state, in tandem with increasing atomic radii, results in an increase of metallic character down the group. silicon already shows some incipient metallic behavior, particularly in the behavior of its oxide compounds and its reaction with acids as well as bases (though this takes some effort), and is hence often referred to as a [[metalloid]] rather than a nonmetal. however, metallicity does not become clear in group 14 until germanium and dominant until tin, with the growing importance of the lower +2 oxidation state.
silicon
all silicon-based approaches would fix the avogadro constant but vary in the details of the definition of the kilogram. one approach would use silicon with all three of its natural isotopes present. about 7.78% of silicon comprises the two heavier isotopes: si and si. as described in " below, this method would "define" the magnitude of the kilogram in terms of a certain number of c atoms by fixing the avogadro constant; the silicon sphere would be the "practical realisation". this approach could accurately delineate the magnitude of the kilogram because the masses of the three silicon nuclides relative to c are known with great precision (relative uncertainties of 1ppb or better). an alternative method for creating a silicon sphere-based kilogram proposes to use isotopic separation techniques to enrich the silicon until it is nearly pure si, which has a relative atomic mass of . with this approach, the avogadro constant would not only be fixed, but so too would the atomic mass of si. as such, the definition of the kilogram would be decoupled from c and the kilogram would instead be defined as atoms of si (≈ fixed moles of si atoms). physicists could elect to define the kilogram in terms of si even when kilogram prototypes are made of natural silicon (all three isotopes present). even with a kilogram definition based on theoretically pure si, a silicon-sphere prototype made of only nearly pure si would necessarily deviate slightly from the defined number of moles of silicon to compensate for various chemical and isotopic impurities as well as the effect of surface oxides.
alternative approaches to redefining the kilogram