Question

The composition of two elements A and B are given below:

Element	A	B
Protons	6	6
Neutrons	6	8
Electrons	6	6

(a) What is the atomic number of A?

(b) What is the atomic number of B?

(c) What is the mass number of A?

(d) What is the mass number of B?

(e) Which element(s) do A and B represent?

Answer 1

Definition of isotopes.

Isotopes are the atoms of the same element which have the same atomic number and different mass numbers.

They have similar chemical properties and different physical properties.

Definition of atomic number.

Atomic number is defined as the number of protons present inside the nucleus of an atom.

Definition of mass number.

Mass number is defined as the sum of number of protons and number of neutrons present inside the nucleus of an atom.

(a) Atomic number = number of protons = number of electrons

Therefore atomic number of A = 6

(b) Atomic number of B = 6

(c) Mass number = number of protons + number of neutrons.

Therefore mass number of A = 12

(d) Mass number of B = 14

(e) Therefore from the above information we can confirm that they are isotopes of carbon.

Carbon-12 - ${}_6{}^{12}\mathrm{C}$ and Carbon-14${}_6{}^{14}\mathrm{C}$.