Draw the orbital diagram of ${}_{20}{}^{40}\mathrm{Ca}^{+2}$ ion and state the number of three fundamental particles present in it.

The subscript of the formula indicates the atomic number and the atomic number of Calcium (Ca) is 20.

Also, the Atomic number= Number of protons

• Therefore, the number of protons= 20

Mass number= Number of protons+ Number of neutrons

From the superscript of the symbol, mass number=40

• Number of neutrons=40-20
• Therefore, the number of neutrons= 20

In a neutral atom, no of protons= number of electrons

• Therefore, the number of electrons in the atom= 20
• The number of electrons present in Calcium ion= 18. This is because a positively charged ion (cation) is formed by the loss of electrons and the +2 charge in the symbol indicates that the Calcium atom has attained this charge by the loss of 2 electrons.
• Hence, number of electrons in the Ca⁺² ion =18 (20-2=18). In the diagram, 18 electrons are shown.