Question

calculate the formal charge on an oxygen atom in H2O .give examples of compounds with incomplete octet n expanded octet​

Answer 1

Answer :  The formal charge of an oxygen atom in $H_2O$ is 0.

The examples of incomplete octet are, $BH_3,AlCl_3,AlH_3$

The examples of expanded octet are, $PCl_5,SF_6,AsF_5$

Explanation :

Lewis-dot structure : It shows the bonding between the atoms of a molecule and it also shows the unpaired electrons present in the molecule.

In the Lewis-dot structure the valance electrons are shown by 'dot'.

The given molecule is, $H_2O$

As we know that hydrogen has '1' valence electron and oxygen has '6' valence electrons.

Therefore, the total number of valence electrons in $H_2O$ = 2(1) + 6 = 8

According to Lewis-dot structure, there are 4 number of bonding electrons and 4 number of non-bonding electrons.

Now we have to determine the formal charge for each atom.

Formula for formal charge :

$\text{Formal charge}=\text{Valence electrons}-\text{Non-bonding electrons}-\frac{\text{Bonding electrons}}{2}$

$\text{Formal charge on O}=6-4-\frac{4}{2}=0$

$\text{Formal charge on }H_1=1-0-\frac{2}{2}=0$

$\text{Formal charge on }H_2=1-0-\frac{2}{2}=0$

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.

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 : $BH_3,AlCl_3,AlH_3$

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 : $PCl_5,SF_6,AsF_5$

Answer 2

Explanation:

The correct answer is +3