Question

Chlorine is an element of atomic number 17. It is a mixture of two isotopes having mass number of 35 and 37.

State the number of protons, electrons and neutrons in the following isotopes: ${{}^{35}\mathrm{Cl}}_{17}$,${{}^{37}\mathrm{Cl}}_{17}$ .

Answer 1

• Isotopes- Atoms of an element having the same atomic number but a different mass number are known as isotopes.
• Atomic number(Z)- The total number of protons in the nucleus of an atom gives us the atomic number of that atom.
• Mass number(A)- The number of protons and neutrons combine to give us the mass number of an atom.

For a neutral atom-

• Atomic number= number of protons= number of electrons
• Number of neutrons=mass number - atomic number=A-Z
• In ${{}^{35}\mathrm{Cl}}_{17}$ the atomic number of chlorine atom is 17 and its mass number is 35.
• Number of neutrons=35-17=18
• In ${{}^{37}\mathrm{Cl}}_{17}$ the atomic number of the chlorine atom is 17 and its mass number is 37.
• Number of neutrons=37-17=20

Isotope	Number of electrons	Number of protons	Number of neutrons
${{}^{35}\mathrm{Cl}}_{17}$	17	17	18
${{}^{37}\mathrm{Cl}}_{17}$	17	17	20