91Ó°ÊÓ

The mass number of the element is the sum of the neutrons and the protons. Also, the number of protons is equal to the atomic number of the elements. Therefore, the atomic number of any element is determined by the number of protons present on that element. Hence,the name of the atom or element is depicted by the number of protons.

In a neutral atom, the number of protons is equal to the number of electrons.

From the ionic depiction of atom (a),

$$\begin{gathered} \mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{proton}\mathbf{=}\mathbf{8} \\ \mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{electrons}\mathbf{=}\mathbf{10} \\ \mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{neutrons}\mathbf{=}\mathbf{9} \end{gathered}$$

Therefore, the atomic number of the ion is equal to the number of protons, that is, 8.

$$\begin{gathered} \mathbf{Mass}\mathbf{}\mathbf{number}\mathbf{=}\mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{proton}\mathbf{+}\mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{neutrons} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\mathbf{8}\mathbf{+}\mathbf{9} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\mathbf{17} \end{gathered}$$

Hence, the atom with the atomic number 8 is Oxygen (O) and belongs to group 6A. It is found in period 2 in the periodic table.

From the ionic depiction of atom (b),

$$\begin{gathered} \mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{proton}\mathbf{=}\mathbf{9} \\ \mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{electrons}\mathbf{=}\mathbf{10} \\ \mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{neutrons}\mathbf{=}\mathbf{10} \end{gathered}$$

Therefore, the atomic number of the ion is equal to the number of protons, that is, 9.

$$\begin{gathered} \mathbf{Mass}\mathbf{}\mathbf{number}\mathbf{=}\mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{proton}\mathbf{+}\mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{neutrons} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\mathbf{9}\mathbf{+}\mathbf{10} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\mathbf{19} \end{gathered}$$

Hence, the atom with the atomic number 9 is Fluorine (F) and belongs to group 7A. It is found in period 2 in the periodic table.

From the ionic depiction of atom (c),

$$\begin{gathered} \mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{proton}\mathbf{=}\mathbf{20} \\ \mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{electrons}\mathbf{=}\mathbf{18} \\ \mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{neutrons}\mathbf{=}\mathbf{20} \end{gathered}$$

Therefore, the atomic number of the ion is equal to the number of protons, that is,20.

$$\begin{gathered} \mathbf{Mass}\mathbf{}\mathbf{number}\mathbf{=}\mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{proton}\mathbf{+}\mathbf{Number}\mathbf{}\mathbf{of}\mathbf{}\mathbf{neutrons} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\mathbf{20}\mathbf{+}\mathbf{20} \\ \mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{}\mathbf{=}\mathbf{40} \end{gathered}$$

Hence, the atom with the atomic number 20 is Calcium (Ca) and belongs to group 2A. It is found in period 4 in the periodic table.