Q.Discuss the general characteristics of Group 15 elements with reference to their electronic configuration, oxidation state, atomic size, ionisation enthalpy and electronegativity.

Step 1: Electronic configuration.

Every Group 15 element (N, P, As, Sb, Bi) has the general valence-shell configuration $ns^2np^3$. The half-filled p-subshell gives extra stability, reflected in unusually high ionisation enthalpy, especially for nitrogen.

Step 2: Oxidation states.

Common oxidation states range from $-3$ to $+5$ (e.g. $-3, +3, +5$). Because of the stable half-filled $p^3$ configuration, N and P can also show $+1, +2, +4$ in some compounds. Down the group, the $+5$ state becomes progressively less stable and the $+3$ state becomes more stable (inert pair effect: the $ns^2$ electrons become increasingly reluctant to participate in bonding due to poor shielding by d/f electrons in the heavier members), so $BiF_5$ (a strong oxidiser) is far less stable relative to $BiF_3$ than $NF_5$ (non-existent) would be to $NF_3$.

Step 3: Atomic/ionic size.

Atomic and ionic radii increase down the group from N to Bi, due to the addition of a new shell at each step (the As–Sb–Bi jump is larger than N–P due to the intervening d/f-block contraction being incompletely compensated).

Step 4: Ionisation enthalpy.

Ionisation enthalpy decreases down the group (N to Bi) because of increasing atomic size and screening, but nitrogen's first ionisation enthalpy is anomalously high (1402 kJ/mol) due to its small size, high nuclear charge, and extra stability of the exactly half-filled $2p^3$ configuration.

Step 5: Electronegativity.

Electronegativity decreases down the group from N (most electronegative element after F, O) to Bi, as atomic size increases and the nucleus's pull on the bonding electron pair weakens.

Work through the five asked properties in order — configuration, oxidation states, size, ionisation enthalpy, electronegativity — stating the trend down the group and flagging nitrogen's anomalies and the inert-pair-effect shift in oxidation-state stability.

• Do not forget the inert pair effect explanation for why $+3$ becomes more stable than $+5$ going down the group (Bi(V) is a strong oxidiser, Bi(III) is the stable state).
• Nitrogen's anomalously high ionisation enthalpy/electronegativity (vs. the smooth group trend) must be called out explicitly, not glossed over.
• Do not state oxidation states as only $+3$/$+5$ — mention $-3$ as the characteristic (most common, especially for N) negative state too.