Question

Which of the given alkaline earth metal is hardest of all alkaline earth metals?
(a). Mg
(b). Ca
(c). Be
(d). Sr

Answer 1

- Hint: Alkaline earth metals (Group - II) are relatively soft metals however, they are harder than the alkali metals of Group I. The hardness of alkaline earth metals decreases down the group. This is because hardness depends on the rigidity of the structure, the arrangement of atoms and the intermolecular forces in the structure.

Complete step-by-step solution -
Alkaline earth metals are metals of group – II. They are generally soft metals, however, they are harder than alkali metals of group – I.
A substance becomes hard or soft, depending on the structure of the atoms of the substance. If the structure is rigid, then the substance will be hard. The greater the amount of intermolecular attractive forces in the substance, the harder the substance is.
The hardness of alkaline earth metals decreases down the group. This is because as we go down the group, the attractive force between the nucleus and the outermost electron decreases as the size of the atom increases. Hence, the intermolecular attractive force also decreases.
The sequence of the elements from top to bottom in the alkaline earth metal group – II is Be, Mg, Ca, Sr, Ba, Rb. Hence, going by the above explanation, the hardest alkaline earth metal is Beryllium (Be).
Hence, option (c) is correct.

Note: Students might get confused since there is a popular saying that having calcium leads to hard, healthy and strong bones, so It must be the hardest alkaline earth metal. However, this is not true since calcium in its raw form is not present in bones but in the form of different compounds which make it hard. Hence, students must understand the explanation given in the answer and therefore, realize which option is correct.