Structure of Atomic Nucleus

The nucleus is the heaviest part of an atom, accounting for 99.9 percent of the atom's total mass. Yet it is extremely tiny, making up only, on average, one ten-thousandth of the atom's size. Nuclei consist of protons and neutrons.

Protons and Neutrons

Protons are the positively charged portions of the nucleus. Neutrons, also found in the nucleus, have a neutral charge.

Force

Protons and neutrons are held together by a strong force, also known as the nuclear force. This force is extremely strong, but covers a limited area.

Atomic Number

The number of protons in the nucleus is called the atomic number. Each element in the periodic table has a different atomic number.

Atomic Mass

The number of neutrons plus the number of protons equal an atom's atomic mass.

Electrons

Electrons are negatively charged particles that surround a nucleus, held in place by electrostatic force. If an atom has more protons than electrons, it has a positive charge. More electrons than protons results in a negative charge.

References

• U.S. Department of Energy, Berkeley Lab: ABCs of Nuclear Science