Question

The position of five elements in the periodic table are shown below:

	Group 1	Group 2	Group 15	Group 16
Period 1		A		B
Period 3	C		D	E

What are the number of valence electrons in B? 

Identify the element(s) which 

(i) will have the smallest atomic radius? 

(ii) will be the most metallic? 

(iii) will form basic oxide? 

(iv) will show valency three? 

(v) will show greatest tendency to gain electron?

Answer 1

Since, we know that elements in 16^th group have 6 electrons in their outer most shell i.e. the valence electrons are 6. Therefore, we can say that B has 6 valence electrons. 

(Note: For this case ignore the period.) 

(i) We know that element in lower period have smaller radius as compared other as they have less no. of shells. Also, going along period the size of atom decreases as the effective nuclear charge on outer electrons increases. So, B will have smallest size as it lies in 1st period and 16th group. 

(ii) We know that, the metallic character increases going down the group and decreases going right along the period. Thus C will be most metallic of all. 

(iii) Since C and A lie in 1^st and 2^nd group so these can readily lose electron and thus can form basic oxides. 

(iv) We know that elements of 15^th group need only three electrons to complete their octet configuration and thus show valency 3. So, D will show valency 3. 

(v) We know that tendency to gain electron or electron gain enthalpy increases going right along period and decreases going down the group. Thus, B will show highest tendency to gain electrons