Concept that all matter is made up of particles.
Elements are made up of particles called
atoms. Atoms are built up from three types of particle:
protons,
neutrons, and
electrons. Other types of particles in matter are
molecules and
ions. A molecule is a small group of atoms that are held together by
covalent bonds. An ion is a charged particle. It is formed by an atom either gaining or losing electrons. The properties of solids, liquids, and gases can be explained by the
kinetic theory of matter, the theory that all matter is made up of very small particles which are in constant motion.
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