Question

Predict the order of reactivity with water for the elements given below. List the LEAST reactive first Fr Sr Вa Cs

Answer 1

The reactivity order is

Sr< Ba< Cs < Fr

From position of elements in periodic table, Cs and Fr are in Group I and Ba and Sr are in Group 2. As we move down the group, the reactivity of elements increase since the nuclear charge as well as the number of shielding electrons increases. Due to the presence of more energy levels, the electrons move farther from nucleus and electrons are loosely held. Therefore it is easy to remove electrons or in other terms reactivity increases.

So, Fr > Cs.

Across the period, though number of electrons increase, the energy levels remain the same, Thus, the electrons are strongly attracted by nucleus and it becomes difficult to remove electrons. Thus reactivity reduces.

Thus, Cs > Ba.

Overall order is Fr > Cs > Ba > Sr