The $1^{\text {st }}, 2^{\text {nd }}$ and the $3^{\text {rd }}$ ionization enthalpies $\mathrm{I}_{1}, \mathrm{I}_{2}$ and $\mathrm{I}_{3}$, of four atoms with atomic numbers $\mathrm{n}, \mathrm{n}+1$, $\mathrm{n}+2$ and $\mathrm{n}+3$, where $\mathrm{n}<10$, are tabulated below. What is the value of n ? | Atomic number | $\mathbf{l}_{\mathbf{1}}$ | $\mathbf{l}_{\mathbf{2}}$ | $\mathrm{l}_{3}$ | | --- | --- | --- | --- | | n | 1681 | 3374 | 6050 | | $\mathrm{n}+1$ | 2081 | 3952 | 6122 | | $\mathrm{n}+2$ | 496 | 4562 | 6910 | | $\mathrm{n}+3$ | 738 | 1451 | 7733 |

Classification of Elements and Periodicity — JEE Advanced · 2020 · 27 Sep 2020 · Paper 2 Question with Solution

The

1^{st}, 2^{nd}

and the

3^{rd}

ionization enthalpies

I_{1}, I_{2}

and

I_{3}

, of four atoms with atomic numbers

n, n + 1

n + 2

and

n + 3

, where

n < 10

, are tabulated below. What is the value of n ?

Atomic number	$l_{1}$	$l_{2}$	$l_{3}$
n	1681	3374	6050
$n + 1$	2081	3952	6122
$n + 2$	496	4562	6910
$n + 3$	738	1451	7733

Answer: 9

Solution

By examining the ionization enthalpy values:

For atomic number

(n + 2)

I_{1} = 496

is very low, but

I_{2} = 4562

is extremely high. This large jump (

I_{2} ≫ I_{1}

) indicates that after removing one electron, the next electron is much harder to remove. This is characteristic of an alkali metal (Group 1) with 1 valence electron.

For atomic number

(n + 3)

I_{1} = 738

and

I_{2} = 1451

are both relatively low, but

I_{3} = 7733

is very high. The jump

I_{3} ≫ I_{2}

indicates 2 valence electrons, characteristic of an alkaline earth metal (Group 2).

If

(n + 2)

is alkali metal and

(n + 3)

is alkaline earth metal, then:

$(n + 1)$ must be a noble gas (Group 18)
$n$ must be a halogen (Group 17)

Since

n < 10

and

n

is a halogen,

n = 9

(Fluorine).

Verification:

n = 9

(F),

n + 1 = 10

(Ne),

n + 2 = 11

(Na),

n + 3 = 12

(Mg) ✓

JEE Advanced · 2020 · 27 Sep 2020 · Paper 2 · Integer answer

JEE Advanced · 2020 · 27 Sep 2020 · Paper 2 · Classification of Elements and Periodicity

Solution

More JEE Advanced questions on Classification of Elements and Periodicity