Consider the hypothetical situation where the azimuthal quantum number, l, takes values $0,1,2, \ldots \ldots . \mathrm{n}+1$, where n is the principal quantum number. Then, the element with atomic number:

(A) 9 is the first alkali metal

(C) 13 has a half - filled valence subshell

(D) 6 has a $2 p$ - valence subshell

JEE Main · 2020 · 03 Sep 2020 · Shift 2 · Atomic Structure

Consider the hypothetical situation where the azimuthal quantum number, l, takes values

0, 1, 2, \dots\dots . n + 1

, where n is the principal quantum number. Then, the element with atomic number:

Answer: (B)

In this imagined scheme the azimuthal number runs up to

n + 1

, so for

n = 1

the allowed subshells are

1 s

1 p

and

1 d

, and filling proceeds in order of increasing

(n + l)

, taking

1 s

before

1 p

. Placing two electrons in

1 s

and six in

1 p

completes a stable closed configuration,

1 s^{2} 1 p^{6}

, at a total of eight electrons. The element of atomic number

8

is therefore the first to reach a noble-gas configuration.

JEE Main · 2020 · 03 Sep 2020 · Shift 2 · Single correct option