Question

Which is the correct order of increasing energy of the listed orbitals in the atom of titanium? (At. No. 22)
(A) 3s 3p 3d 4s
(B) 3s 3p 4s 3d
(C) 3s 4s 3p 3d
(D) 4s 3s 3p 3d

Answer 1

Hint: Write the electronic configuration of titanium. Recollect the order in which filling of electrons in the orbitals takes place. The question is asking us to write the increasing order of energies of the orbitals of titanium atoms. Think about the principle or rule which governs the way in which electronic configuration is written.

Complete step by step solution:
- Titanium is a d-block element in the periodic table. It has atomic number 22. Its electronic configuration is given as,
$${}^{22}Ti=1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^2$$
- The filling of electrons in the orbitals is in accordance with Aufbau’s rule.
- According to Aufbau’s rule, the electrons will start filling in orbitals having lowest energy and then move on to orbitals having higher energy. Aufbau’s rule states that the electrons will be filled in orbitals according to their increasing order of energies.
- Aufbau’s rule is represented as,

- The order of energy of different orbitals in an atom is given below,
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p
- Therefore, the correct order of increasing energy of the listed orbitals in the atom of titanium is 3s 3p 4s 3d.

- Therefore, the correct answer is option (B).

Note: Remember the electrons are filled up in the orbitals in increasing order of their energies. The principle which tells us about the sequence in which electrons will get filled up in the orbitals is known as Aufbau’s principle. 1s orbital has the lowest energy.