Page 20 - Chemistry_Form_2

Chemistry
for Secondary Schools

Isotopes

Task 1.6

Watch educational video on isotopes and explain the uses of isotopes in carbon
dating, medicine and agriculture.
FOR ONLINE READING ONLY

Atoms of the same element have the same number of protons. However, the
number of neutrons in the atoms of the same element may vary. This means that
the atomic number of an element does not vary but the mass number can vary.
Such atoms of an element are called isotopes. Isotopes are atoms of the same
element with the same number of protons but different number of neutrons. Such
an existence of the element is called isotopy. Isotopy is the existence of atoms of
the same element having the same atomic number but different mass numbers. It
is also possible to get the number of sub-atomic particles in a given isotope.

Example 1.3

State the number of protons, neutrons, and electrons in the following isotopes:

12
14
(a) C and C
6 6
3
(b) H , H and H
1
2
1
1
1
Solution
12
(a) C, Mass number = 12
6
Number of protons = atomic number = 6
Number of electrons = number of protons = 6
Number of neutrons = 12 – 6 = 6
14 C , Mass number = 14
6
Number of protons = 6
Number of electrons = 6
Number of neutrons = 14 – 6 = 8

(b) 1 1 H, Mass number = 1
Number of proton = 1

Number of electron = 1
Number of neutron = 1 – 1 = 0

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