Question

An atom has electronic configuration $2,8,7$. What is the atomic number of this element?

Answer 1

Atomic number

• The number of protons present in the nucleus is equal to the atomic number.
• The atomic number is represented as Z.
• $\text{Atomic number=Number of protons=Number of electrons in neutral atom}$

Atomic number of element

• The electronic configuration of atom is $2,8,7$.
• So, the total number of electrons is $2+8+7=17$.
• So, the atomic number of this element is $17$.
• An element with an atomic number $17$ is chlorine.
• The symbol for chlorine is $\mathrm{Cl}$.
• The electronic configuration of chlorine is $1s^{2}2s^{2}2p^{6}3s^{2}3p^5$.