Question

List any two properties of the elements belonging to the first group of the modern periodic table.

Answer 1

1. First group elements

The first group of elements is also known as alkali metals. There are six elements in group 1. The name of the elements are Hydrogen (H), Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), and Cesium (Cs). All the elements of group 1, except Hydrogen, are metals and have low ionization enthalpy. Alkali metals have the largest size in their respective groups as the effective nuclear charge increases across the group.

2. Properties of alkali metals

Two properties of the elements belonging to the first group of the modern periodic table are:

1. All the elements contain only one electron in their valence shell: The general outer electronic configuration of an alkali metal is ${\mathrm{ns}}^1$ where n is the principal quantum number of the valence shell. For example, the electronic configuration of Lithium is:

$\mathrm{Li}-1{\mathrm{s}}^{2}2{\mathrm{s}}^1$

Similarly for Sodium,

$\mathrm{Na}-1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^1$

Therefore, the number of valence electrons in the outer electron shell is the same for both Lithium and Sodium even if the number of shells in the atom is different.

2. All the elements are electropositive in nature: Electropositivity refers to the ability to form a positive ion by the removal of electrons from the atom. The electrons removed are generally valence electrons. The valency of alkali metals is 1. Therefore, they remove one electron from the valence shell to attain a stable electron configuration.

The ionization enthalpies of the alkali metals are very low because of their larger size. Therefore, less energy is required to remove the valence electron or they are highly electropositive.

For example, Lithium forms monovalent Lithium ions by the removal of one electron.

$$\begin{gathered} \mathrm{Li}\to {\mathrm{Li}}^{+}+{\mathrm{e}}^{-} \\ \left(\mathrm{Lithium}\right)(\mathrm{Lithium}\mathrm{ion}) \end{gathered}$$

The electronic configuration of Lithium ion is:

${\mathrm{Li}}^{+}-1{\mathrm{s}}^2$

This is a stable configuration. Therefore, Lithium ion is easily formed from Lithium which makes it electropositive.