Question

Which is more metallic, sodium or aluminium?

Answer 1

Hint: Metallic character means the level of reactivity as that of a metal. Metallic property of a metal is determined by its tendency to lose electrons. Try to answer this on the basis of ionization energy as metals tend to lose electrons. Also recall that metallic character decreases on going from left to right along a period in periodic table. Now by using this you can answer the given question.

Complete step by step answer:
To answer this, firstly let us discuss what ionization energy is and how it affects metallic character.
The least amount of energy required to remove the loosely bound electron of an atom is termed as the ionization energy. Thus, metallic character increases as ionization energy decreases.
When we move from left to right along the period the ionization energy increases. This is due to the fact that the newly added electrons are poorly shielded thus effective nuclear charge increases and this leads to increase in ionization energy.Now let us discuss sodium and aluminium.
We know that the atomic number of aluminium is 13 and that of sodium is 11. If we write their electronic configurations, it will be $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{1}}$ for aluminium and $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{1}}$ for sodium.

We can see that sodium and aluminium are in the same period (3) and electrons in aluminium are added in the same shell as that of sodium. Thus, the effective nuclear charge is more on aluminium than sodium and thus aluminium has a smaller size.
Thus, removal of electrons from aluminium requires higher energy than sodium i.e. ionization energy of aluminium is higher than sodium. This makes sodium more metallic than aluminium.
Also, upon losing one electron sodium will gain a stable nearest noble gas configuration thus it will lose electrons readily.
Therefore, from the above argument we can clearly say that sodium is more metallic than aluminium as it will lose one electron readily hence owns metallic character and this is the required answer.

Note: Remember that removal of electrons results in an increase in effective nuclear charge and consequently causes contraction in size of the atom. Hence, greater amount of energy is required to remove electrons from more compact and smaller cations. Thus, magnesium has lower first ionization energy and high second ionization energy.