The Nucleus the "center" of an atom basically explains the question. The nucleus, that dense central core of the atom, contains both protons and neutrons. Electrons are outside the nucleus in energy levels. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge.

A neutral atom contains equal numbers of protons and electrons. But the number of neutrons with an atom of a particular element can vary. Atoms of the same element have differing numbers of neutrons are called isotopes.

More Info: en.wikipedia.org