Question

What is an atom and what is atomic number?

Answer 1

An atom is a fundamental particle of matter (matter is anything that can be touched physically). Everything in the universe (except energy) is made of matter, and so, everything in the universe is made of atoms.
An atom itself is made up of three particles called subatomic particles:protons, neutrons, and electrons. The proton and the neutron make up the center of the atom called the nucleus and electrons revolve around the nucleus. The electron carries a negative charge and the proton carries a positive charge. Atom is neutral as the number of protons and the number of electrons are equal.
The number of proton in an atom is called its atomic number. It is of great importance because chemical properties of an element depend upon this number.