Question

Answer the following questions:
(A) Explain Isotopes, Isobars and Isotones along with examples. [3 Marks]​

(B) The atomic composition of element A is as follows: number of neutrons = x, atomic mass = 12, number of electrons = 6. The atomic composition of B is as follows: number of neutrons = y, atomic mass = 28, number of electrons = number of electrons in A + 8. Compute the ratio of x to y. [2 Marks]

Answer 1

(A) Isotopes have the same number of protons with different number of neutrons. Example: Isotopes of hydrogen: Protium ($1H1$), Deuterium ($1H2$), Tritium ($1H3$). [1 Mark]​

Isobars have the same number of nucleons (sum of protons and neutrons). Example: $16S40$, $17\mathrm{Cl}40$. [1 Mark]

​Isotones have same number of neutrons but different number of protons. Example: $19K39$, and $20\mathrm{Ca}40$. [1 Mark]​ ​

(B) Element A is carbon (Number of electrons = 6 = Atomic number)
Number of neutrons = x = 12 – 6 = 6 [0.5 Marks]
Element B is silicon.
Number of electrons in A + 8 = 6 + 8 = 14 [0.5 Marks]
Number of neutrons = y = 28 – 14 = 14 [0.5 Marks]

x = 6 and y = 14
The ratio of x to y is:
x:y = 6:14 = 3:7 [0.5 Marks]