Question

The symbol of Helium atom is ${}_2{}^4\mathrm{He}$ . How many neutrons are present in ${\mathrm{He}}^{+2}$ ion?

Answer 1

• The symbol of He atom is ${}_2{}^4\mathrm{He}$ . This symbol, represents the chemical name and electronic information in the atom.
• The superscript represents the mass number which is the sum of number of neutrons and protons.
• The subscript represents the Atomic number which is the number of electrons present in the atom.
• For helium, its mass number is 4 and Atomic number is 2.
• We know that, in a neutral atom, the$\mathrm{number}\mathrm{of}\mathrm{electrons}=\mathrm{number}\mathrm{of}\mathrm{protons}$. Therefore, the number of protons in He is 2.
• Subtracting the number of protons from Mass number we get the number of neutrons, i.e., 2
• . $$\begin{gathered} \mathrm{Mass}\mathrm{number}=\mathrm{Number}\mathrm{of}\mathrm{neutrons}+\mathrm{Number}\mathrm{of}\mathrm{protons} \\ 4=\mathrm{n}+2 \\ \mathrm{n}=4-2 \\ \mathrm{n},\mathrm{Number}\mathrm{of}\mathrm{neutrons}=2 \end{gathered}$$
• In the given ${\mathrm{He}}^{+2}$ ion, He loses 2 electrons thus, the number of electrons is 0 and the number of protons is 2. The number of neutrons present in the ion will be 4-2 =2