​Protons are the only true way to identify an atom.

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Electrons and neutrons can be different from the periodic table.

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When protons change, it changes to the next element.​

To Find:

​Protons---look at the atomic number

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Neutrons--Mass # - atomic #

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Electrons--same as protons--look at atomic #​

​Remember:

Protons and electrons are the same #.

They are the same number---which makes the atoms neutral (no electrical charge)​​

If you can't find # of protons, look for electrons​

​What are valence electrons?

Valence electrons determine reactivity.​

They are found on the last energy level of an atom. Farthest from the nucleus.​

The group number, tells the number of valence electrons.

1A, 2A, 3A, 4A, etc. We want A's not B's.​

Reactive vs Non-reactive atoms

The # of valence electrons determines how reactive the atom is.​

8 valence electrons---non-reactive

less than 8 valence electrons--reactive​

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Group 1 is the most reactive.

Group 18 is the least reactive.​