Octet rule defined

The use of resonance structures such as 7 and 8 to describe bond polarity led to a subtle change in the meaning of the octet rule, namely, that an atom obeys the octet rule if it does not have more than eight electrons in its valence shell. As a result, resonance structures such as 7 and 8 are considered to be consistent with the octet rule. However, this is not the sense in which Lewis used the octet rule. According to Lewis, a structure such as 7 would not obey the octet rule because there are only three pairs of electrons in the valence shell of carbon, just as BF3 does not obey the octet rule for the same reason. Clearly the octet rule as defined by Lewis is not valid for hypervalent molecules, which do, indeed, have more than four pairs of shared electrons in the valence shell of the central atom. 

Consider a molecular skeleton composed of n main-group atoms, M , which takes the form of a chain, ring, cage, or framework. Let g be the total number of valence electrons of the molecular skeleton. When a covalent bond is formed between two M atoms, each of them effectively gains one electron in its valence shell. In order to satisfy the octet rule for the whole skeleton, 5 (Sn—g) electron pairs must be involved in bonding between the M atoms. The number of these bonding electron pairs is defined as the bond valence b of the molecular skeleton ... 

There is a well defined relationship between the chemical structure of a Zintl phase and its electronic structure. For the majority of these compounds, AX homopolar X-X contacts are present and can be explained as two-electron, two-center bonds. The octet rule [5] is fijlfiUed for the A and for the X atoms. This is provided by a formal charge transfer of the valence electrons fiom A to X leading to... 

The bond orders we are considering are the ones defined in terms of the classical structural formulae, which can be related to the numbers of bonding and anti-bonding electrons. They are not the bond orders derived from molecular orbital numerical calculations as given by Eq. (9.45). An additional uniformity involving such bond orders and chemical equations can be found, directly related to the octet rule. For example, by considering... 

The i-block elements (with the exceptions of H and He) do not have sufficient electrons for hypervalent bonding. Transition metals can use d orbitals in their bonding, and thus do not follow the octet rule. Therefore, with the exception of hydrogen bonding, the central atom in a hypervalent system must be a / -block element. Within the p block, two obvious issues are how the bond strengths change as the central atom A is varied across or down the periodic table. Sufficient data is currently available to begin to define these periodic trends. 

Definitions. Define and illustrate the following terms (a) octet rule, (b) Lewis symbol, (c) ionic bond, (d) covalent bond, (e) crystal lattice energy, (f) Iree radical, (g) network covalent compound, (h) electronegativity, (i) polar molecule, (j) dipole moment, (k) formal charge, (1) oxidation number, (m) hydrogen bond, (n) dipole-dipole attraction, (o) London forces. 

In reference to neon define and explain the significance of (a) noble gas, (b) octet of outer shell electrons, (c) noble gas outer electron configuration, (d) octet rule. 

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