Usage - Pronoun-Antecedent Agreement. A pronoun is a word used to stand for (or take the place of) a noun. A word can refer to an earlier noun or pronoun in the sentence. Example:
A subatomic particle is a unit of matter or energy that's the fundamental makeup of all matter. According to modern atomic theory, an atom has a nucleus, which is its center, or core. The nucleus contains subatomic particles: protons and neutrons. Protons are positively-charged particles. Neutrons are neutral particles.
Structure of the Atom. Protons are positively charged particles found in the nucleus; All atoms of the same element have the same number of protons; One proton weighs 1 atomic mass unit (amu or u); Neutrons are particles found in the nucleus, but have no charge; One neutron also weighs 1 amu.