8: Counting Atoms, Ions, and Molecules
- Page ID
- 367063
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- 8.1: Counting Atoms by the Gram
- In chemistry, it is impossible to deal with a single atom or molecule because we can't see them or count them or weigh them. Chemists have selected a number of particles with which to work that is convenient. Since molecules are extremely small, you may suspect this number is going to be very large and you are right. The number of particles in this group is Avagadro's number and the name of this group is the mole.
- 8.2: Counting Molecules by the Gram
- The molecular mass of a substance is the sum of the average masses of the atoms in one molecule of a substance. Calculations for formula mass and molecular mass are described. Calculations involving conversions between moles of a material and the mass of that material are described. Calculations are illustrated for conversions between mass and number of particles.
- 8.3: Chemical Formulas as Conversion Factors
- Using formulas to indicate how many atoms of each element we have in a substance, we can relate the number of moles of molecules to the number of moles of atoms. In any given formula the ratio of the number of moles of molecules (or formula units) to the number of moles of atoms can be used as a conversion factor.
- 8.4: Mass Percent Composition of Compounds
- Chemists often need to know what elements are present in a compound and in what percentage. The percent composition is the percent by mass of each element in a compound.
- 8.5: Mass Percent Composition from a Chemical Formula
- The percent composition of a compound can also be determined from the formula of the compound. The subscripts in the formula are first used to calculate the mass of each element in one mole of the compound. This is divided by the molar mass of the compound and multiplied by 100%.