Question

How many electrons, protons and neutrons are there in a nucleus of atomic number 11 and mass number 24?
(i) Number of electrons = ________.
(ii) Number of protons = ________.
(iii) Number of neutrons = _______.

Answer 1

Hint: We are given the atomic number and mass number of an atom. We are asked to find the number of electrons, number of protons and number of neutrons in the nucleus of the given atom. We know the relation between numbers of at electrons, protons, neutrons and atomic number and mass number of the atom. Using this relation we can solve the question.

Complete answer:
In the question we are given the atomic number and atomic mass of an atom.
Let ‘Z’ be the atomic number of the atom, then
 Z = 11
Let ‘A’ be the atomic mass of the atom, then
A = 24
We need to find the total number of electrons, protons and neutrons in the nucleus of this atom.
First let us find the total number of protons in the nucleus.
We know that the atomic number of an atom is the number of protons in the atom.
Therefore the total number of atoms in the nucleus of this atom = atomic number (Z) = 11
Now let us find the total number of electrons in the nucleus of this atom.
We can assume that the given atom is a neutral atom since it is not specified in the question.
We know that for a neutral atom the total number of electrons is same as the total number of protons in the atom
Hence the number of electrons = number of protons = atomic number = 11
Next we need to find the total number of neutrons in the atom.
We know that the number of neutrons is the difference of atomic number and atomic mass of the atom.
Therefore,
Total number of neutrons in the atom = A – Z = 24 – 11 = 13
Hence we can conclude that,
(i) Number of electron = 11
(ii) Number of protons = 11
(iii) Number of neutrons = 13

Note:
In an atom the protons and neutrons are located inside the nucleus of the atom. Unlike them the electrons are found outside the nucleus. They are negatively charged particles.
Protons along with neutrons are found at the centre of the atom, the nucleus. We know that protons are positively charged particles and neutrons do not have any charge.
We know that for a neutral atom the number of protons equals the number of electrons. When they are equal, since they are oppositely charged the net charge becomes zero and the atom will be neutral.