Protons have an charge of +1 and electrons have a charge of -1 but neutrons have no charge
Atomic number = number of protons (also number of electrons)
Mass number = number of protons + neutrons
The electrons in an atom are arranged in energy levels or shells
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The periodic table
Elements in the same group in the periodic table have the same number of electrons in their highest energy level and this gives them similar properties
The elements in Group 0 of the periodic table are called the noble gases. They're unreactive because their atoms have stable arrangements of electrons
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Chemical reactions
When elements react, their atoms join with other atoms to form compounds and this involves giving, taking or sharing electrons to form ions or molecules
Compounds formed from metals and non-metals consist of ions
Compounds formed from non-metals consist of molecules where the atoms are held together by covalent bonds
Chemical reactions can be represented by word equations or by symbol equations
No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants
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