Consider the following elements :
Ca, Cl, Na, I, Li, Ba, Sr, K, Br
Separate these elements into three groups (families) of similar properties. State one property in each case on the basis of which you have made your choice.
(i) Lithium (Li), sodium (Na) and potassium (K) are three metals of group 1 having a valency of 1.
(ii) Calcium (Ca), strontium (Sr) and barium (Ba) are three metals of group 2 having a valency of 2.
(iii) Chlorine (Cl), bromine(Br) and iodine (I) are three non-metals of group 17 which are known as halogens, and have seven valence electrons.