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mole

The SI base unit used to measure the amount of a substance, abbreviated mol; one mole is the amount of a pure substance that contains 6.02x10^23 representative particles.

Avogadro's number

The number 6.0221367x10^23, which is the number of representative particles in a mole, and can be rounded to three significant digits: 6.02x10^23.

molar mass

The mass in grams of one mole of any pure substance.

percent composition

The percent by mass of each element in a compound.

empirical formula

A formula that shows the smallest whole-number ratio of the elements in a compound, and may or may not be the same as the actual molecular formula.

molecular formula

A formula that specifies the actual number of atoms of each element in one molecule or formula unit of the substance.

hydrate

A compound has a specific number of water molecules bound to its atoms.