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Give reasons for the following:-

1. In the d-block Elements the size is on almost comparable, that is, there is no significant change in the size.

2. In group-13, Boron to Aluminium size increases but from Aluminium to Gallium size decreases and again from Gallium to Indium size increases but from Indium to Thallium, there is very slight increase in size.

3. In the f-block, left to right size decreases very sharply.

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Answer:

Properties and Periodic Trends

These elements are found in Group 13 (XIII) of the p block in the Periodic Table of Elements. Aluminum, gallium, indium, and thallium are metallic. They each have three electrons in their outermost shell (a full s orbital and one electron in the p orbital) with the valence electron configuration ns2np1. The boron family adopts oxidation states +3 or +1. The +3 oxidation states are favorable except for the heavier elements, such as Tl, which prefer the +1 oxidation state due to its stability; this is known as the inert pair effect. The elements generally follow periodic trends except for certain Tl deviations:

Atomic radius increases down the group (Tl has the largest atomic radius.)

Electrode potential increases down the group (reactivity decreases down the group)

Ionization Energy decreases going down the group (because the electrons are farther from the core and therefore are easier to remove; Tl does not fit this trend)*

Table 1: Properties & Trends of Group 3 ElementsBoronB510.8112076-801AluminumAl1326,9815660-1.68578GalliumGa3169.72329.8-0.56558IndiumIn49114.8181560.34558ThalliumTh81205.383303+0.72589

Boron

Boron is the first element of Group 13 and is the only metalloid of the group. Its chemical symbol is B, and it has an atomic number of 5. Boron has the electron configuration [He] 2s22p1and prefers an oxidation state of +3.