Home Chemistry Classification of Elements and Periodicity Ionisation Energy According to I. C. slater effective nuclear …
Chemistry Classification of Elements and Periodicity Ionisation Energy Single Correct MCQ
Published on: August 14, 2026

According to I. C. slater effective nuclear charge , Z * , due to screening , is not exactly equal to the actual nuclear charge Z of the nucleus of the atom. Z * depends on the type of orbital in which the electron is housed , and on the ability of other electrons in more penetrating orbitals to screen the electron in question from the nucleus.

The relative extent to which the various orbitals penetrate the electron clouds of other orbitals is
s > p > d > f. The effective nuclear charge Z * due to screening is given by , Z * = Z – σ

Where Z is the atomic number and σ is the slater screening constant values : 0 < σ < Z

Electrons

in orbitals

s or p orbital

σ per electron in orbital

n

(n – 1)

(n – 2),

(n – 3), etc

0.35

0.85

1.00

d or f orbital

0.35

1.00

1.00

Screening effect of one electron in the outer most orbital, is not considered in calculation of σ .

(i)What is the value of Z * for Rb (37) ?

A
1.7 29 Ionisation energy increases as Z * increases
B
1.3 24.8 Electronegativity of the atom increases as Z * increases
C
2.2 2.2 The ionisation energy of Na, K , Rb , are comparable because of equal Z *
D
34.8 (ii)What is Z * for Cu (29) ? 4.2 (iii)In which of the following cases the concept of Z * is applicable ? All of the above

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Text Solution

Verified by Experts
The correct answer is:
A

(i)

Sol. 1 s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 σ = 8 × 0.85 + 18 × 1 + 8 × 1 + 2 × 1 = 34.8

Z

* = 37 – 34.8 = 2.2

(ii)

Sol. 1 s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 1 σ = 10 × 1 + 8 ×0.85 + 8 × 1 + 2 × 1 = 26.8

Z

* = 29 – 26.8 = 2.2

(iii)

Sol. All of the above

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