1. Atomic Mass

2. Atomic mass is the mass of an atom in atomic mass units (amu)
Micro World
atoms & molecules
Macro World
grams
Atomic mass is the mass of an atom in atomic mass units (amu)
By definition:
1 atom 12C “weighs” 12 amu
On this scale
1H = amu
16O = amu

3. The average atomic mass is the weighted average of all of the naturally occurring isotopes of the element.

4. … = x + Average Atomic mass of an element ( % abundance of Isotope #1) +
Isotope #2 …

5. Silver has two naturally occurring isotopes.
Ag-107 has an abundance of 51.82% and mass of amu. Ag-109 has a relative abundance of 48.18% and a mass of amu. Calculate the average atomic mass of silver.

6. Rubidium is a soft, silvery-white metal that has two common isotopes, Rb and Rb. If the abundance of 85Rb is 72.2% with an atomic mass of amu and the abundance of 87Rb is 27.8% with an atomic mass of amu, what is the average atomic mass of rubidium? 85 37 87 37

7. Copper, a metal known since ancient times, is used in electrical cables and pennies, among other things.
The atomic masses of its two stable isotopes, (69.09 percent) and (30.91 percent), are amu and amu, respectively.
Calculate the average atomic mass of copper. The relative abundances are given in parentheses.

8. Average atomic mass (63.55)

9. Mass Spectrometry Heavy Light
Most accurate way to analyze substances by mass

10. Light
Mass Spectrum of Ne
Heavy

12. Formula mass is the sum of the atomic masses (in amu) in a formula unit of an ionic compound.
Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule.
SO2 1S
32.07 amu
NaCl
1Na
22.99 amu 2O
+ 2 x amu
1Cl
amu
SO2
64.07 amu
NaCl
58.44 amu
1 molecule SO2 = amu
1 formula unit NaCl = amu

13. Calculate the molecular masses (in amu) of the following compounds:
sulfur dioxide (SO2), a gas that is responsible for acid rain
caffeine (C8H10N4O2), a stimulant present in tea, coffee, and cola beverages

14. Avogadro’s number (NA)
The Mole (mol): SI base unit to measure the amount of a substance
(count numbers of particles)
Pair = 2
Dozen = 12
The mole (mol) is the SI base unit to measure the amount of a substance (used to count numbers of particles)
1 mol = NA = x 1023
Avogadro’s number (NA)

15. Molar mass is the mass of 1 mole of in grams molecules formula units
atoms
Molar mass is the mass of 1 mole of in grams
molecules
formula units
1 mole 12C atoms = x 1023 atoms = g
1 12C atom = amu
For any element
atomic mass (amu) = molar mass (grams)
1 atom of Li = amu
1 mole of Li atoms = g Li
For any ionic compound
formula mass (amu) = molar mass (grams)
1 formula unit NaCl = amu
1 mole NaCl = g NaCl
For any molecule
molecular mass (amu) = molar mass (grams)
1 molecule SO2 = amu
1 mole SO2 = g SO2

16. One Mole of: S C Hg Cu Fe

17. M = molar mass in g/mol
NA = Avogadro’s number

18. Helium (He) is a valuable gas used in industry, low-temperature research, deep-sea diving tanks, and balloons.
How many moles of He atoms are in 6.46 g of He?

19. Zinc (Zn) is a silvery metal that is used in making brass (with copper) and in plating iron to prevent corrosion.
How many grams of Zn are in mole of Zn?

20. Sulfur (S) is a nonmetallic element that is present in coal.
When coal is burned, sulfur is converted to sulfur dioxide and eventually to sulfuric acid that gives rise to the acid rain phenomenon.
How many atoms are in 16.3 g of S?

21. A sample of aluminum chloride (AlCl3) has a mass of 35. 6 g
A sample of aluminum chloride (AlCl3) has a mass of 35.6 g. How many chloride ions are present?

22. How many oxygen atoms are in 37
How many oxygen atoms are in 37.5 grams of the molecular compound sulfur trioxide (SO3)