Question

State octel rule.explain its inadequacies with respect to
a.incomplete octel
b. expanded octel​

Answer 1

Explanation:

Incomplete Octet

There are certain atoms of certain elements that can exist in stable compounds forming bonds with less than eight valence electrons. When this occurs, the atom of the element within the molecule is said to contain an incomplete octet.

The common examples of such elements are hydrogen (stable with only 2 valence electrons), beryllium (stable with only 4 valence electrons) and boron and aluminum (stable with only 6 valence electrons). For hydrogen 2 valence electrons give it a noble gas structure (like He) so this is much like the octet rule for everything else below period 1.

Expanded octet:

Expanded octet occurs when an atom is able to have more than 8 valence electrons. For example, in SO₃, the sulfur atom forms 6 covalent bonds, hence it has 12 valence electrons. Expansion of octet is possible only from Period 3 elements onwards, due to the presence of low-lying empty d orbitals that can accommodate the extra electrons.

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Answer 2

Answer :

Octet rule :

In order to attain stability the atoms tends to have eight electrons in its valence shell which can be obtained by either by sharing of electrons of complete transfer of electrons.

The tendency of atoms to attempt to get a noble gas configuration that is eight valence electrons is said to be octet rule.

For example : As we know that the sodium has one valence electron, so if giving it up then the result in the same electron configuration as the neon and chlorine has seven valence electrons, so if it takes one it will have eight and the result in the same electronic configuration as the argon.

Incomplete octet :

When the atoms have less than eight electrons in its valence shell then they tend to react and form the more stable compounds.

For example : $BH_3$

Expanded octet :

When the atoms have more than eight electrons in its valence shell then they tend to react and form the more stable compounds.

For example : $PCl_5$