An atom consists of a nucleus with a positive denser part at the center and negative electrons revolving around the nucleus. So splitting an atom actually means splitting the nucleus.

When the nucleus is bombarded with high energy neutrons, it splits up. Upon splitting, it releases a huge amount of energy (nuclear energy), daughter nuclei, and neutrons. This phenomenon is known as nuclear fission.

It should be noted that, in order for the atoms to split up spontaneously, the neutron to proton (N/Z) ratio must be greater than 1. That is why only unstable radioactive atoms and in some cases unstable isotopes with heavy nuclei split up to become stable.

For example

Uranium-235, when bombarded with high energy neutrons, splits up into daughter nuclei i.e. Ba and Kr along with the production of an enormous amount of energy.

1n + 235U → 144Ba + 90Kr + 2n1

ΔE = -200MeV

The obtained nuclear energy is used to generate electricity in nuclear power plants. Specifically, it is utilized to heat the water chamber, producing steam, which in turn runs the turbine.