Describe the general trends in the following properties of the elements in groups 13
(a) Atomic size
(b) Metallic character
(c) Oxidation states

Explanation

For Group 13
(a) Atomic size On moving down the group for each successive member, one extra shell of electrons is added and therefore, atomic radius is expected to increase. However, a deviation can be seen
Atomic radius of Ga is less than that of Al due to presence of additional 10d- electrons, which offer poor screening effect to the outer electron
(b) Metallic or Electropositive Character Boron is semi-metal (melalloid) due to very high ionisation enthalpy. All others are metals and metallic character first increases from B to Al as size increases. From Al to Tl decrease due to poor shielding of d- and f-electrons
(c ) Oxidation States As we move down the group, the stability of +3 oxidation state decreases while that of +1 oxidation progressively increases. In other words, the order of stability of +1 oxidation state increase in the order. `Al lt Ga lt ln lt Tl`. Infact, in Ga, ln and Tl, both +1 and +3 oxidation states are observed.