Maya, you are right. Neutrons, electrons and protons are all parts of an atom.
When do you think these were discovered? Let me show you the timescale
In 1808 a teacher and scientist called John Dalton discovered the atom.
In 1897 the electron was discovered by a scientist called J.J.Thomson
in 1911 the proton was discovered by a scientist called Rutherford
In 1932 Earnest Chadwick discovered the neutron
All this happened in 124 years! and the final bit ‘the electron’ was only discovered 87 years ago and you are now learning about it. I shall let my friends tell you a little bit about these particles.