1. 10.1 Chemical Measurement

2. How do we measure the mass of an atom?
Atomic mass: the mass of an atom expressed relative to the mass assigned to carbon-12
Common atomic masses: (we will always use 2 places behind the decimal)
Hydrogen: amu
Carbon: amu
Oxygen: amu

3. How do we measure the mass of a molecule?
Molecules are just several atoms chemically combined together, so…
Formula mass: the sum of all atomic masses of all the atoms in a compound
Ex: H H’s, so 2 x 1.01 = 2.02
1 O, so 1 x = 16.00
Add them together, you get 18.02, so one molecule of water has a mass of amu.

4. Find the mass of … An atom of bromine Diatomic bromine
A molecule of carbonic acid (H2CO3)
Answers:
Atom of bromine = amu
Diatomic bromine = amu
Molecule of carbonic acid = amu

5. But why do we need to measure the mass of atoms and molecules?
Well, most of the time we don’t!
But we do need to measure bigger amounts.
We do this using the concept of a mole!
Well, not one quite like this!

6. Mole:
(Def): of any element, the number of atoms of that element equal to the number of atoms in exactly 12.0 grams of carbon-12.
This ends up being 6.02 x 1023 atoms.
This is the number of atoms in 1 mole of any element.
It is called Avogadro’s number (named after an Italian chemist and physicist)

7. So, how do you find a mole of an atom?
Exactly as you found the atomic mass! The only difference is that it is measured in grams.
Remember that hydrogen had an atomic mass of 1.01 amu?
Well, the mass of one mole of hydrogen is 1.01 grams!
This is called the molar mass – the mass, in grams, of one mole of a substance
ADDITION: units for molar mass = g/mol

8. Look at the comparison . . . Element Number of atoms in one mole
Mass of one mole
Copper
6.02 x 1023
63.55 g
Mercury g
Sulfur
32.07 g
Iron
55.85 g

9. What about molecules? Same thing!
Earlier, we found the formula mass of water to be amu.
Well, one mole of water (which is 6.02 x 1023 molecules) has a mass of g.

10. One last note on particles…
Three words that may confuse you…
An ATOM is the smallest part of an element. (ex: One mole of carbon has a mass of g)
A MOLECULE is the smallest part of a covalent or molecular compound. (Ex: one mole of water has a mass of g)
A FORMULA UNIT is the smallest part of an ionic substance. (Ex: one mole of sodium chloride has a mass of g)

11. Looking at it another way…
Smallest particle is…
One mole has ___ particles
One mole has a mass of …
Carbon (C)
Atom
6.02 x 1023 atoms
12.01 g
Water (H20)
Molecule
6.02 x 1023 molecules
18.02 g
Sodium Chloride
(NaCl)
Formula unit
6.02 x 1023 formula units
58.44 g