Question

Explain with examples
(i) Atomic number,
(ii) Mass number,
(iii) Isotopes
(iv) Isobars.
Give any two uses of isotopes.

Answer 1

(i) Atomic number: The atomic number of an element is the total number of protons present in the atom of that element. For example, nitrogen has 7 protons in its atom. Thus, the atomic number of nitrogen is 7.

---

(ii) Mass number: The mass number of an element is the sum of the number of protons and neutrons present in the atom of that element. For example, the atom of boron has 5 protons and 6 neutrons. So, the mass number of boron is 5 + 6 = 11.

---

(iii) Isotopes: These are atoms of the same element having the same atomic number, but different mass numbers. For example, chlorine has two isotopes with atomic number 17 but mass numbers 35 and 37 represented by \(^{35} C_{17},\, \)\(^{37} C_{17}\).

---

(iv) Isobars: These are atoms having the same mass number, but different atomic numbers i.e., isobars are atoms of different elements having the same mass number. For example, Ne has atomic number 10 and sodium has atomic number 11 but both of them have mass numbers as 22 represented by - \(^{22}Ne_{10},\) \(^{22}Ne_{11}.\)

Two uses of isotopes:
→ One isotope of uranium is used as a fuel in nuclear reactors. 
→ One isotope of cobalt is used in the treatment of cancer.