Chemistry / Unit 3 Chem 0364 short lesson, about 20 seconds
Formula Mass for Ionic Compounds
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The idea
An ionic compound's formula mass sums the average atomic masses of every ion shown in its formula unit, cation and anion together.
In practice
Sodium chloride's formula mass adds sodium's average mass to chlorine's, since NaCl's formula unit contains exactly one of each ion.
Where people slip
Ionic compounds form no discrete molecules, so their formula mass is never correctly called a molecular mass.
Your place on the trail
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