Lithium, sodium and potassium formed a group called alkali metal group. Their similar properties are:
(i) All these elements are metals.
(ii) All these react readily with water to form alkalies and hydrogen gas.
(iii) All of them have a valency of 1.
Döbereiner suggested the following triads:
(i) Alkali metal family—Li, Na, K
(ii) Alkaline earth family—Ca, Sr, Ba
(iii) Halogen family—CI, Br, I
Tips: -
Consider the following elements:
K, I, Li, Sr, CI, Mg, Br, Ca, Na.
Separate these elements in three groups or triads having similar properties. State one property in each case on the basis of which groups are separated.
These elements can be separated into three groups as given below:
(a) K, Li, Na—have valency of (+1).
(b) Sr, Mg, Ca—have valency of (+2).
(c) I, CI, Br—have valency of (-1).