Discuss the pattern of variation in the oxidation states of(i) B to Tl (ii) C to Pb.

The variation in oxidation states across the elements of a group or period often reflects underlying trends in electronic configurations and chemical reactivity. Let's explore the pattern of oxidation states for the elements:

(i) Boron (B) to Thallium (Tl):

• Boron (B): Boron typically exhibits an oxidation state of +3 in its compounds, as it prefers to lose its three valence electrons to achieve a stable electronic configuration.
• Aluminum (Al): Aluminum predominantly shows an oxidation state of +3 in its compounds, similar to boron, due to the loss of its three valence electrons.
• Gallium (Ga): Gallium mainly displays an oxidation state of +3, following the trend set by boron and aluminum.
• Indium (In): Indium is more versatile in its oxidation states compared to the preceding elements. It can exhibit both +1 and +3 oxidation states, with the +3 oxidation state being more common.
• Thallium (Tl): Thallium, like indium, shows a wider range of oxidation states. It can exhibit +1, +3, and even +5 oxidation states. However, the +1 oxidation state is more stable and common than the +3 or +5 states.

The trend across this group shows a general progression from +3 oxidation state (B, Al, Ga) to a more varied set of oxidation states as we move down the group, with elements like indium and thallium displaying a wider range of oxidation states due to the increasing ease of losing electrons as we move down the group.

(ii) Carbon (C) to Lead (Pb):

• Carbon (C): Carbon typically exhibits oxidation states of -4 (in compounds like methane) to +4 (in compounds like carbon dioxide). However, its most common oxidation states are +4 in carbon dioxide and -4 in methane.
• Silicon (Si): Silicon primarily shows oxidation states of +4 (in compounds like silicon dioxide) and sometimes +2 (in compounds like silane, although less common).
• Germanium (Ge): Germanium mainly exhibits an oxidation state of +4, following the trend set by carbon and silicon.
• Tin (Sn): Tin is more versatile in its oxidation states compared to the preceding elements. It can exhibit oxidation states of +2 and +4, with the +2 oxidation state being more common.
• Lead (Pb): Lead, like tin, can exhibit multiple oxidation states. It commonly shows oxidation states of +2 and +4, with the +2 oxidation state being more stable and common.

The trend across this group shows a general progression from a wider range of oxidation states (-4 to +4) for carbon to a narrower range of oxidation states (+2 to +4) for lead. This narrowing occurs due to the increasing size and decreasing electronegativity of the elements as we move down the group, making it less favorable for higher oxidation states to be stabilized.