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Standard X

Chemistry

Spin Quantum Number

Which of the ...

Question

Which of the following represents the set of quantum numbers for the last electron filled in beryllium?

n = 1, l = 0,

m_{l}

= 0,

m_{s}

= 0

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n = 1, l = 1,

m_{l}

= + 1,

m_{s}

= + 1/2

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n = 2, l = 0,

m_{l}

= 0,

m_{s}

= - 1/2

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n = 2, l = 1,

m_{l}

= 0,

m_{s}

= 0

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Solution

The correct option is C n = 2, l = 0, $m_{l}$ = 0, $m_{s}$ = - 1/2
Each electron in an atom is described by a set of four quantum numbers n, l, $m_{l}$ and $m_{s}$ .
Here n = principal quantum number
l = azimuthal quantum number
$m_{l}$ = magnetic quantum number
$m_{s}$ = spin quantum number.
Beryllium has 4 electrons.
So, electronic configuration of beryllium is $1 s^{2} 2 s^{2}$ .
Thus, last electron is filled in 2s orbital. Hence, n = 2, l = 0, and $m_{l}$ = 0 and electron can have any spin positive or negative.
So, set of quantum number could be n = 2, l = 0, $m_{l}$ = 0, $m_{s}$ = - 1/2

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Similar questions

Q. Arrange the electrons represented by the following sets of quantum numbers in decreasing order of energy.
(i)

n = 4, l = 0, m_{l} = 0, m_{s} = + \frac{1}{2}

(ii)

n = 3, l = 1, m_{l} = 1, m_{s} = - \frac{1}{2}

(iii)

n = 3, l = 2, m_{l} = 0, m_{s} = + \frac{1}{2}

(iv)

n = 3, l = 0, m_{l} = 0, m_{s} = - \frac{1}{2}

Q. The quantum number of four electrons are given below:
I.

n = 4, l = 2, m_{l} = - 2, m_{s} = - 1 / 2

II.

n = 3, l = 2, m_{l} = 1, m_{s} = + 1 / 2

III.

n = 4, l = 1, m_{l} = 0, m_{s} = + 1 / 2

IV.

n = 3, l = 1, m_{l} = 1, m_{s} = - 1 / 2

The correct order of their increasing energies will be:

Q. Explain giving reasons which of the following sets of quantum numbers are not possible.
(a )

n = 0

l = 0

m_{1} = 0

m_{s} = + 1 / 2

(b)

n = 1

l = 0

m_{1} = 0

m_{s} = - 1 / 2

(c)

n = 1

l = 1

m_{1} = 0

m_{s} = + 1 / 2

(d)

n = 2

l = 1

m_{1} = 0

m_{s} = - 1 / 2

(e)

n = 2

l = 3

m_{1} = - 3

m_{s} = + 1 / 2

(f)

n = 3

l = 1

m_{1} = 0

m_{s} = + 1 / 2

Explain, giving reasons, which of the following sets of quantum numbers are not possible.
a) n = 0 l = 0 ml = 0 $m, = + \frac{1}{2}$
b) n = 1 l = 0 ml = 0 $m, = - \frac{1}{2}$
c) n = 1 l = 1 ml = 0 $m, = + \frac{1}{2}$
d) n = 2 l = 1 ml = 0 $m, = - \frac{1}{2}$
e) n = 3 l = 3 ml = – 3 $m, = + \frac{1}{2}$
f) n = 3 l = 1 ml = 0 $m, = + \frac{1}{2}$

Question 18

Out of the following pairs of electrons, identify the pairs of electrons present in degenerate orbitals.

(a) (i) $n = 3, l = 2, m_{l} = - 2, m_{s} = - \frac{1}{2}$ (ii) $n = 3, l = 2, m_{l} = - 1, m_{s} = - \frac{1}{2}$

(b) (i) $n = 3, l = 1, m_{l} = 1, m_{s} = + \frac{1}{2}$ (ii) $n = 3, l = 2, m_{l} = - 1, m_{s} = + \frac{1}{2}$

(d) (i) $n = 3, l = 2, m_{l} = + 2, m_{s} = - \frac{1}{2}$ (ii) $n = 3, l = 2, m_{l} = + 2, m_{s} = + \frac{1}{2}$

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