Chemistry (school) · Part 01
Atoms and matter
What everything is made of, and how atoms are built.
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- AtomThe smallest piece of an element that still counts as that element. Everything around you is built from atoms.
- ElementA substance made of only one kind of atom. Each element has its own symbol, such as O for oxygen.
- CompoundA substance made of two or more different elements joined together by chemical bonds. It can only be split up by a chemical reaction.
- MixtureTwo or more substances that are mixed but not chemically joined. Each keeps its own properties and can be separated by physical methods.
- ProtonA particle inside the nucleus of an atom with a positive charge. Its relative mass is 1.
- NeutronA particle inside the nucleus with no charge. Its relative mass is 1, the same as a proton.
- ElectronA tiny particle with a negative charge that moves around the nucleus. Its mass is almost nothing compared with a proton.
- Atomic numberThe number of protons in an atom. It is the number that identifies the element.
- Mass numberThe total number of protons plus neutrons in the nucleus of an atom. Electrons are too light to count.
- IsotopeAtoms of the same element with the same number of protons but different numbers of neutrons. They behave the same in reactions but differ in mass.