‘Valency is also the number of electrons – donated or accepted by an atom so as to achieve the stable electronic configuration of the nearest noble gas’. With reference to this definition –
State why the valency of sodium, magnesium and aluminium is: +1, +2 & +3 respectively.
Valency is the number of electrons donated or lost from the valence shell. Since sodium donates 1 valence electron its valency is +1.
Magnesium loses 2 electrons and aluminium loses 3 electrons from their valence shell their valency is
+2 – magnesium
+3 – Aluminium