Question

(a) Write down the electronic configuration of (i) sodium atom, and (ii) chlorine atom.
(b) How many electrons are there in the outermost shell of (i) a sodium atom, and (ii) a chlorine atom?
(c) Show the formation of NaCl from sodium and chlorine atoms by the transfer of electron(s).
(d) Why has sodium chloride a high melting point?
(e) Name the anode and the cathode used in the electrolytic refining of impure copper metal.

Answer 1

(a) (i) Atomic number of sodium is 11.
Its electric configuration is $$\begin{gathered} \mathrm{K}\mathrm{L}\mathrm{M} \\ 281 \end{gathered}$$.
(ii) Atomic number of chlorine is 17.
Its electronic configuration is $$\begin{gathered} \mathrm{K}\mathrm{L}\mathrm{M} \\ 287 \end{gathered}$$.
(b) (i) In a sodium atom, the number of electrons present in its outermost shell (M shell) is one.
(ii) In a chlorine atom, the number of electrons present in its outermost shell (M shell) is seven.

(c) Sodium and chlorine contain one and seven electrons, respectively, in their outermost shells. Hence, sodium transfers its one electron to chlorine atom and their octets get stabilised.
$\stackrel{.}{\mathrm{Na}}$ + $:\underset{..}{\overset{.}{\mathrm{Cl}:}}$$\to$ ${\mathrm{Na}}^{+}{\left[\underset{..}{\overset{..}{:\mathrm{Cl}}}:\right]}^{-}$ or $\mathrm{NaCl}$

In a sodium chloride molecule, sodium atom transfers its one electron to chlorine atom to form an ionic bond.

(d) Sodium chloride contains positively charged sodium atom and negatively charged chlorine atom. Due to these oppositely charged species, there is a strong intermolecular force between them. Hence, it requires huge amount of energy to break this strong intermolecular force and melt the salt. Therefore, sodium chloride has a high melting point.

(e) In the electrolytic refining of impure copper metal, anode is the electrode at which oxidation takes place and cathode is the electrode at which reduction takes place.
Hence, at anode, a thick block of impure copper metal is used from which pure metal oxidises to copper ion in the solution.
At cathode, a thin strip of pure copper metal is used where copper ions from the solution reduce to copper metal and get deposited on the strip.