Question

Identify the elements with the following property and arrange them in increasing order of their reactivity:

(a) An element that is a soft and reactive metal

(b) The metal which is an important constituent of limestone

(c) The metal which exists in a liquid state at room temperature

Answer 1

Part 1: Identifying the element

(a) A soft and reactive metal:

• Sodium is an alkali metal, it is soft and can be cut by a knife.
• The atomic number of Sodium$\left(\mathrm{Na}\right)$ is 11 and the electronic configuration can be written as$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^1$.
• Sodium can easily lose one electron from its outermost to attain noble gas electronic configuration.
• It reacts vigorously with water to form Hydrogen gas and release heat.

(b) An important constituent of limestone:

• Limestone has the chemical formula CaCO₃
• Calcium is the main component of limestone and its chemical name is calcium carbonate.
• Calcium is an alkaline earth metal.
• The atomic number of calcium is 20 and the electronic configuration can be written as $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^2$.

(c) Metal that exists in the liquid state at room temperature:

• Mercury exists as a liquid at room temperature.
• Mercury is a transition metal.
• The atomic number of mercury$\left(\mathrm{Hg}\right)$ is 80 and the electronic configuration can be written as$\left[\mathrm{Xe}\right]4{\mathrm{f}}^{14}5{\mathrm{d}}^{10}6{\mathrm{s}}^2$

Part 2: Increasing order of reactivity:

• From the reactivity series, Sodium is present above both metals and Calcium is present above mercury.
• So, Sodium is highly reactive than both these metals and calcium is more reactive than mercury.
• So, the increasing order of their reactivity is $\mathrm{Hg}<\mathrm{Ca}<\mathrm{Na}$.