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Elements, Compounds and Mixtures

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Additional Notes

Atom: Smallest particle of an element

Molecule: Combination of two or more atoms of the same element

Element: Composed of only one type of atom and cannot be broken down into simpler substances by chemical methods

Compound: a substance containing two or more elements chemically joined together (eg NaCl)

Mixture: consists of 2 or more substances not chemically combined together

Group (columns): Elements in a group share similar chemical and physical properties

Period (rows): Elements in a period have the same number of energy shell

Mass number: Number of protons + neutrons

Atomic number: Number of protons

 Pure compound
 has fixed % by mass of each element
has variable composition by mass of each element
 has a chemical formula
does not have a chemical formula
 cannot be separated into its elements by physical means
can be easily separated into its components by physical means
 has fixed melting and boiling points
no fixed melting and boiling points