Question

Describe the general trends in the following properties of the elements in Groups $13$ and Group $14$.

A Atomic size

B Ionisation enthalpy

C Metallic character

D Oxidation states

E Nature of halides

Answer 1

$\text{Properties of Group 13 elements}:$

A. $\text{ATOMIC SIZE}$

• Down the group, atomic radius increases
• There is an exception where atomic radius of Gallium is less than that of Aluminium
• Because Gallium has $10$ electrons in $3d$ subshell and $d$ orbital has poor screening of nuclear charge than $s$ and $p$ orbital.
• Therefore, nuclear charge increases, and atomic radius of gallium ($135$ pm) is less than that of Aluminium ($143$ pm).

Therefore, atomic size order is

$B<Ga<Al<In<Tl$

$\text{Properties of Group 14 elements}:$

A. $\text{ATOMIC SIZE}$

• Down the group, covalent radius increases from carbon to silicon and then from Silicon to Lead a small increase is observed due to presence of completely filled $d$ and $f$ orbital in heavy members.

Therefore, atomic size order is

$C>Si>Ge>Sn>Pb$



$\text{Properties of Group 13 elements}:$

B. $\text{IONISATION ENTHALPY}$

• First Ionisation enthalpy does not decrease down the group as expected.
• There is a decreasing trend from $B$ to $Al$ with increase in size.
• The discontinuity occur in $Al$ to $Ga$ and $In$ to $Tl$ due to inability of $d$ and $f$ orbital to screen the nuclear charge as they have low screening effect.

Therefore, $I{E}_1$ order is

$B>Tl>Ga>Al>In.$

$\text{Properties of Group 14 elements}:$

B. $\text{IONISATION ENTHALPY}$

• First ionisation enthalpy decreases from silicon to Tin then show a slight increase in Ionisation enthalpy from Tin to lead due to the poor shielding effect of $d$ and $f$ orbitals in Lead.

Therefore, order is

$C<Si<Ge<Sn<Pb.$



$\text{Properties of Group 13 elements}:$

C. $\text{METALLIC CHARACTER}$

• Metallic character increases down the group. Boron is non-metallic in nature while all other elements are metals.
• $Tl$ has more metallic character Therefore, order of metallic character is $B<Al<Ga<In<Tl$

$\text{Properties of Group 14 elements}:$

C. $\text{METALLIC CHARACTER}$

• Metallic character increases down the group.
• Carbon and Silicon are non-metals, germanium is metalloid and tin and lead are soft Metals.
• Therefore, order of metallic character is $C<Si<Ge<Sn<Pb$

$\text{Properties of Group 13 elements}:$

D. $\text{OXIDATION STATE}$

• All the elements of group $13$ shows oxidation of $+3$.
• Boron has a small size and first $3$ ionisation enthalpy are very high, which prevent boron to form $+3$ oxidation state and force boron to form only covalent compounds.
• $Al$ always form compound in $+3$ oxidation state.
• $Ga,In$, and $Tl$ shows both $+1$ and $+3$ oxidation state. The compound in $+1$ oxidation state is more ionic than $+3$ oxidation state.
• Due to the inert pair effect. the stability of $+3$ oxidation decreases down the group and stability of $+1$ oxidation state increases down the group.

$\text{Properties of Group 14 elements}:$

D. $\text{OXIDATION STATE}$

• Common oxidation states are $+2$ and $+4$
• Carbon and Silicon forms compounds in $+4$ oxidation state.
• Germanium is stable in $+4$ oxidation state and some compound of Germanium in $+2$ states.
• Tin forms compounds in both $+2$ and $+4$ states and Tin is a reducing agent in $+2$ states.
• Lead is a strong oxidising agent in $+4$ oxidation state and very stable in $+2$ oxidation state due to inert pair effect.

$\text{Properties of Group 13 elements}:$

E. $\text{NATURE OF HALIDES}$

• All elements react with halogens to form trihalides except $Tl$.
• The trichloride, tribromide, triiodide covalent in nature.
• The monomeric trihalides are electron deficient so-called as strong Lewis acid.

$\text{Properties of Group 14 elements}:$

E. $\text{NATURE OF HALIDES}$

• The element can form halides of $M{X}_2$ and $M{X}_4,X$ can be $F,Cl,Br,I$.
• Mostly $M{X}_4$ is covalent in nature.
• $Sn{F}_4$ and $Pb{F}_4$ are exceptions as they are ionic in nature.
• $Pb{I}_4$ does not exist.
• $Ge$ and $Pb$ make the formula of $M{X}_2$. Down the group stability of dihalides increases.