All matter is made up of atoms. An atom is like a tiny solar system. In the center of the atom is the nucleus which is a cluster of protons and neutrons. The
protons have a
positive electric charge while the
neutrons are electrically
neutral. The nucleus makes up almost all of an atom's mass or weight. Whirling at fantastic speeds around the nucleus are smaller and lighter particles called
electrons which have a
negative electric charge.
An atom has the same number of electrons (- ve charge) and protons (+ ve charge) to make the atom electrically neutral. An extremely powerful force, called the nuclear force, holds the protons together in the nucleus as they naturally repelled one another electrically.
The atoms of each
chemical element have a different nucleus. An atom of hydrogen has one proton and no neutrons. An atom of nitrogen has 7 protons and 7 neutrons. Heavy elements have a large number of protons and neutrons. For example, the most common
isotope of uranium, uranium-238 has 92 protons and 146 neutrons in its nucleus.
The drawing on the left shows a
carbon atom with 6 protons, 6 neutrons and 6 electrons.
