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.
Each atom is made of a nucleus-containing protons and neutrons-surrounded by electrons. The atomic number is the number of protons in an atom. The elements are arranged in the periodic table in ascending order of atomic number. The mass number of an atom is the total of protons plus neutrons.his means the nucleus of an atom is always positively charged. An atom has a neutral overall charge because it has the same number of electrons as protons. Protons and neutrons have the same mass.