1. Chemical Measurements
Objectives:
1. Define the mole and explain its importance.
2. Explain the meaning of Avogadro's number.
3. Explain how molar mass relates the number of particles of a substance to the mass of a substance.
4. Distinguish between molar mass and formula mass.
Key Terms:
Atomic mass, Formula mass, mole, Avogadro's number, Molar mass

2. Atomic & Formula Mass Atomic Mass Formula Mass
The atomic mass number lists the mass in amu (atomic mass unit) notation.
This number is based on the mass of the carbon-12 atom
Example: H = 1.01amu, O = 16.00amu, C = 12.01amu
The number is rarely an even whole number due to the fractional abundances of the isotopes
Formula Mass
Formula mass is determined by adding all of the masses of atoms in a molecule
Example: H2O = 18.02amu CO2 = 44.01amu NaHCO3 = 84.01amu
Using Masses in Chemical Reactions
masses of the reactants need to equal the masses of the molecules and products.

3. Mole and Avogadro's number
the amu has no real experimental significance in the laboratory setting,
The mole is was defined by Avogadro
A mole is a standard quantity of a substance
all moles have the exact number of atoms in 12 grams of carbon-12
A mole of any element is its amu value expressed in the unit gram
Each mole contains 6.02 x 1023 pieces
Each mole of gas occupies 22.4L at STP
This helps scientists convert the atoms and molecules into a useful and predictable units.

4. Molar mass Molar mass can be used to convert to particles
O = 16amu = 16g = 6.02 x 1023 atoms
O2 = 32amu = 32g = 6.02 x 1023 molecules = x 1023atoms (2 x 6.02 x 1023 atoms)
Avogadro's number (6.02 x 1023) established a direct relationship between the mass, quantity, and volume of an item.