Question

Elements X, Y and Z have atomic numbers 6, 9 and 12 respectively. Which one has four electrons in its valence shell?
(A) X
(B) Y
(C) Z
(D) Both A and B

Answer 1

Hint: Valence shell is the shell of the element in which the last electron gets filled. We can assign electronic configurations to all of them and hence we can find the number of valence shell electrons by adding the electrons present in all the orbitals of the valence shell.

Complete step by step solution:
Let’s see the electronic configuration of each of the given elements in order to find out which one of them will have four electrons in its valence shell.
- Atomic number shows the number of electrons and protons present in the element.
- Valence shell means the valence orbit of the element which can be shown by the ‘n’ in its valence orbital.
i) X, Atomic number = 6
- So, we can say that there will be 6 electrons in X. Let’s arrange them according to Aufbau and Hund’s rules.
- If we arrange the electrons, we can find that 2 electrons will be there in 1s orbital, 2 will be there in 2s orbital and 2 electrons will be present in 2p orbital. So, the electronic configuration of X will be: $1{{s}^{2}}2{{s}^{2}}2{{p}^{2}}$
- So, we can say that in its valence shell it involves 2s and 2p orbitals. So, it will have 2+2 = 4 electrons in its valence shell.
ii) Y, Atomic number = 9
- This element will have a total of 9 electrons. Let’s assign it an electronic configuration.
- It will have 2 electrons in 1s orbital, 2 in 2s orbital and 5 in 2p orbital. So, its electronic configuration will be $1{{s}^{2}}2{{s}^{2}}2{{p}^{5}}$.
- We can see that 2s and 2p orbitals are involved in its valence shell. So, it will have 2+5 = 7 electrons in its valence shell.
iii) Z, atomic number = 12
- This element will have a total of 12 electrons. Let’s assign it an electronic configuration.
- It will have 2 electrons in 1s orbital, 2 in 2s orbital, 6 in 2p orbital and 2 in 3s orbital. So, its electronic configuration will be $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}$.
- We can see that 3s is the only orbital of the valence shell. So, there will be two electrons in the valence shell of Z.

So, we can say that X will have four electrons in its valence shell.
Hence, option (A) is correct

Note: Do not get confused between shell and orbitals. Actually, shells and orbit are the same. Also, subshells and orbitals are the same. So, we can say that orbitals are part of the shell. Here, we are asked to give the number of electrons in valence orbit or shell, so make sure that you do not misinterpret it as the number of electrons in valence orbital.