Name: Electronic Configuration of Elements
Uploaded: 2019-07-19
Duration: 6 min 6 s
Description: The number of protons in an atom is called its atomic number, represented by ‘Z’, while the sum of its protons and neutrons is called its mass number, given...

Question

The first ionization enthalpy values (in $kJ {mol}^{- 1}$ ) of group $- 13$ elements are:

$B$	$Al$	$Ga$	$In$	$Tl$
$801$	$577$	$579$	$558$	$589$

How would you explain this deviation from the general trend?

Accepted Answer

Generally, on moving down the group, ionization enthalpy generally decreases due to an increase in the atomic size and shielding.
Ionization energy $\propto \frac{1}{atomic size}$ .

Ionization energy $\propto \frac{1}{shielding effect}$ .

Thus, on moving down the group, ionization enthalpy decreases from $B$ to $Al$ . But, $Ga$ has higher ionization enthalpy than $Al$ . The $Al$ follows immediately after the $577$ block elements, whereas, the $Ga$ follows after the $558$ block elements. The shielding provided by the $d -$ electrons are not very effective. These electrons do not shield the valence electrons very effectively. As a result, the valence electrons of $Ga$ experience a greater effective nuclear charge than those of $Al$ . Further, moving from $Ga$ to $In$ , the ionization enthalpy decreases due to an increase in the atomic size and shielding. But, on moving from $In$ to $Tl$ , the ionization enthalpy again increases. In the periodic table, $Tl$ follows after the $4 f$ and the $5 d$ electrons. The shielding provided by the electrons in both these orbitals is not very effective. Therefore, the valence electron is held quite strongly by the nucleus. Hence, the ionization energy of $Tl$ is on the higher side.

The first ionization enthalpy values (in $kJ {mol}^{- 1}$ ) of group $- 13$ elements are:

$B$ $Al$ $Ga$ $In$ $Tl$

$801$ $577$ $579$ $558$ $589$

How would you explain this deviation from the general trend?

Important Questions on Classification of Elements and Periodicity in Properties

Learn and Prepare for any exam you want !

The first ionization enthalpy values (in kJ mol-1) of group-13 elements are: B Al Ga In Tl 801 577 579 558 589 How would you explain this deviation from the general trend?

Important Questions on Classification of Elements and Periodicity in Properties

Learn and Prepare for any exam you want !

The first ionization enthalpy values (in $kJ {mol}^{- 1}$ ) of group $- 13$ elements are:

$B$ $Al$ $Ga$ $In$ $Tl$

$801$ $577$ $579$ $558$ $589$

How would you explain this deviation from the general trend?