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Element
Contains one type of atom. Cannot be separated into anything simpler
Compound
Contains two or more element chemically combined. It is in fixed proportions and can only be broken done chemically eg H₂0
Mixture
Can be separated physically. Can be in any proportion
Atom
Smallest part of an element
Nucleus
Where protons and neutrons are tightly packed together. Positively charged
Shells
Where electrons are found orbiting the nucleus
Mass number
The number of protons and neutrons in the nucleus of an atom
Atomic number
The number of protons inside the nucleus of an atom
Isotopes
Different atoms of the same elements with the same number of protons and electrons but different numbers of neutrons in their nuclei
Relative atomic mass (Ar)
Mass of each atom of an element on a scale where 1 atom of 12C is exactly 12
Relative molecular mass (Mr)
Mass of each molecule on a scale where 1 atom of 12C is exactly 12
Relative formula mass
Mass of each formula unit on a scale where 1 atom of 12C is exactly 12
Ion
An atom or group of atoms that has an electrical charge, either positive or negative
Cation
An atom that loses electrons has more protons than electrons and has a positive overall charge
Anion
An atom that gains electrons has more electrons than protons so it has a negative overall charge
Ionic compound
Formed when electrons are transferred from a metal atom to a non metal atom during a reaction
Ionic bond
The electrostatic attraction between oppsitively charged ions
Ionic structure
Regular arrangements of ions held together by electeostatic attraction between oppsitively charged ions
Covalent bond
Sharing a pair of electrons between two atoms
Molecules
Two or more atoms covalently bonded together. They have no charge because they have an equal number of protons and electrons
Note 
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