​Valence Electrons are the electrons on the outermost edge

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Bohr models with 1 or 7 valence electrons are highly reactive

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Group 18 the noble gases are non- reactive ​

​Groups - go up and down there are 18

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Period go side to side there are 7 ​

​Elements that are in the same group have similar characteristics

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Elements in the same period have the same number of energy levels ​

​Counting atoms

small numbers are subscripts they tell us the number of atoms ​

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Large numbers are coefficients they tell us the number of molecules

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You have to multiply the entire formula by the coefficient ​