Classification of Elements and Periodicity in Properties — Chemistry STD 11 Science — Question

In p-block, when we move from left to right in a period, the acidic character of the oxides increases due to increase in electronegativity. For example,

In 2^nd period B₂O₃ < CO₂ < N₂O₃ (acidic nature increases).

In 3^rd period A1₂O₃ < SiO₂ < P₄O₁₀ < SO₃ < C1₂O₇ (acidic character increases).

On moving down the group, acidic character decreases and basic character increases, e.g.,

2. Nature of oxides of 15 group elements.

$\text{N}_2\text{O}_5\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{P}_4\text{O}_{10}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{As}_4\text{O}_{10}\ \ \ \ \ \ \ \ \ \ \text{Sb}_4\text{O}_{10}\ \ \ \ \ \ \ \ \ \ \text{Bl}_2\text{O}_3\\ ^\text{Strongly acidic}\ \ \ \ \ \ \ \ \ ^\text{Moderately acidic}\ \ \ \ \ \ \ \ \ \ \ ^\text{Amphoteric}\ \ \ \ \ \ \ \ ^\text{Amphoteric}\ \ \ \ \ \ \ \ \ \ ^\text{Basic}$

Among the oxides of same element, higher the oxidation state of the element, stronger is the acid. For example, SO₃ is a stronger acid than SO₂.

B₂O₃ is weakly acidic and on dissolution in water, it forms orthoboric acid. Orthoboric acid does not act as a protonic acid (it does not ionise) but acts as a weak Lewis acid.

$\text{B}_2\text{O}_3\ \ \ \ \ \ \ \ \ \ +\ \ \ \ \ \ \ 3\text{H}_2\text{O}\ \ \ \rightleftharpoons\ \ \ \ 2\text{H}_3\text{BO}_3\\^\text{Boron trioxide}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Orthoboric acid}$

$\text{B(OH)}_3\ +\ \text{H}-\text{OH}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ }\big[\text{B}(\text{OH})_4\big]^{-}+\text{H}^+$

Al₂O₃ is amphoteric in nature. It is insoluble in water but dissolves in alkalies and reacts with acids.

$\text{Al}_2\text{O}_3\ \ +\ \ 2\text{NaOH}\ \xrightarrow{\ \ \ \ \ \ \ {\Delta} \ \ \ \ \ \ \ \ }\ 2\text{NaAlO}_2\ \ +\ \ \text{H}_2\text{O}\\ ^\text{Aluminium}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Sodium meta}\\ \ \ ^\text{trioxide}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{chloride}$

$\text{Al}_2\text{O}_3\ \ +\ \ 6\text{HCl}\ \xrightarrow{\ \ \ \ \ \ \ {\Delta} \ \ \ \ \ \ \ \ }\ 2\text{AlCl}_3\ \ +\ \ 3\text{H}_2\text{O}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Aluminium}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{chloride}$

Tl₂O is as basic as NaOH due to its lower oxidation state (+1).

$\text{Tl}_2\text{O}\ +\ 2\text{HCl}\ \xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ }2\text{TlCl}\ +\ \text{H}_2\text{O}$