Question

The order of filling of electrons in the orbitals of an atom will be:

A.3d, 4s, 4p, 4d, 5s
B.4s, 3d, 5s, 4d
C.5s, 4p, 3d, 5s
D.3d,4p, 4s, 4d, 5s

Answer 1

Hint:We know that electronic configuration of an atom is the arrangements of electrons in the orbitals of an atom. In this electronic arrangement, orbitals possessing less energy are filled first and then filled the higher energy orbitals.

Complete step by step answer:Here, to identify the energy of the orbitals we have to use the n+l rule. ‘n’ indicates the principal quantum number and l represents azimuthal quantum number.

Let’s discuss both the quantum numbers. Principal (n) quantum number indicates the principal shell of an atom. Its value starts from 1 to any natural number. In 2s orbital, 2 is the principal number.

The azimuthal quantum number (l) indicates the shape of the orbital. Its value is always less than the value of n. For s, p, d and f subshell, its value is 0,1,2 and 3.

Now, come to the question. We are given five orbitals namely, 3d, 4s, 4p, 4d, 5s and we have to arrange them in order of increasing energy as electrons are filled in that way.

First, we calculate the energy of 3d. Here, the value of n is 3 and the value of l is 2.

So, $ \Rightarrow n + l = {\rm{3}} + {\rm{2}} = {\rm{5}}$

Now, we calculate energy of 4s. Here, the value of n is 4 and the value of l is 0.

So, $ \Rightarrow n + l = 4 + 0 = 4$

Now, we calculate energy of 4p. Here, the value of n is 4 and the value of l is 1.

So, $ \Rightarrow n + l = 4 + 1 = 5$

Now, we calculate the energy of 4d. Here, the value of n is 4 and the value of l is 2.

So, $ \Rightarrow n + l = 4 + 2 = 6$

Now, we calculate the energy of 5s. Here, the value of n is 5 and the value of l is 0.

So, $ \Rightarrow n + l = 5 + 0 = 5$

So, the order of orbitals in increasing is,

4s< 3d <4p <5s <4d

Therefore, order of filling of orbitals is correct 4s, 3d, 5s, 4d. Hence, the correct answer is option B.


Note: Aufbau principle is used in determining electronic configuration of atoms. This principle states that electrons should be filled in lower energy orbitals first and then filled in the higher energy orbitals. And the n+l rule helps to determine the energy of orbitals.