Protons and Neutrons

The nucleus is made up of positively charged protons and uncharged (neutral) neutrons. Protons are made up of three quarks, two up quarks and one down quark. The quarks are held together by strong nuclear forces mediated by gluons.

The neutron has a mass slightly greater than the proton; neutrons are also made up of three quarks, but, as opposed to the proton, one up and two down also held together by strong nuclear forces mediated by gluons.

The number of protons in the nucleus determines the charge on the nucleus and also identifies the element and determines its chemical properties. The number of protons in a nucleus is known as the atomic number of the element. The number of neutrons in the nucleus defines the isotope of the element. Different isotopes of an element have different atomic weights but have the same chemical characteristics although some isotopes will be stable and some isotopes will be radioactive.