Question

Helium atoms have an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Answer 1

Hint: Atom is the smallest fundamental particle of matter. The subatomic particles of an atom are protons, neutrons and electrons. Atomic mass is the sum of the number of protons and neutrons.

Formula Used:
Atomic mass = Number of protons + Number of neutrons

Complete answer:
Protons are positively charged particles, neutrons are neutral particles and electrons are negatively charged particles. Protons and neutrons present in the nucleus of an atom while electrons revolve around the nucleus.
Atomic mass indicates the total number of protons and neutrons present in the nucleus of an atom.
Calculate the number of neutrons present in a helium atom using the following formula.
Atomic mass = Number of protons + Number of neutrons
We have given atomic mass and number of protons of helium.
Atomic mass of helium = 4 u
Number of protons = 2
Now, substitute the given value in the atomic mass formula and calculate the number of neutrons as follows:
4 = 2 + Number of neutrons
Number of neutrons = 4 - 2
Number of neutrons = 2

Hence, the number of neutrons in the helium atom is 2.

Additional Information An atom is the smallest individual particle of an element that takes part in the chemical reaction. Atoms consist of three basic subatomic particles. They are protons, neutrons and electrons. The atomic number of an atom indicates the number of protons present in an atom while the atomic mass number indicates the total number of protons and neutrons. In a neutral atom the number of electrons is always equal to the number of protons.
The helium atom contains 2 protons, 2 neutrons and 2 electrons so the structure of the helium atom is

Note: Atomic number is the number of protons present in the nucleus of an atom. Atomic mass is the total number of protons and neutrons present in the nucleus of an atom. The numbers of neutrons are always less than the atomic mass number.