2.  How do we use these?  These indicate which of the elements make up a substance.  These also indicate the number of ions or atoms that make up a given substance. C 6 H 12 O 6

3.  Atomic mass is the weighted average of the masses of the isotopes of that element.  This reflects the mass and the relative abundance of the isotopes as they occur in nature.

4.  A mole is a unit of measurement of number of atoms of an element ◦ 602,200,000,000,000,000,000,000 atoms are in one mole of an element. ◦ 1 mole = 6.022 x 10 23 particles ◦ This is called Avogadro’s number  The atomic mass of an element is the mass of one mole of that element in grams ( g / mol ).  Using moles allows us to work with formulas in a measurable way – using grams.

5.  One mole of an element is equal to its atomic mass in grams Equals 1 mole of Nitrogen 6.022 x 10 23 atoms of Nitrogen 14.007 g of Nitrogen

6. The mole is how we can measure something … …very small (atoms of an element) …in a manner that we can see (mass in grams). For Bromine, the mass of one mole is 79.9 grams. This is also the mass of 6.022 x 10 23 particles of Bromine … AND one mole of Bromine is 6.022 x 10 23 particles of Bromine

7.  As you know, a mole reflects 6.022 x 10 23 representative particles.  What is a representative particle?  A representative particle is one piece of the substance …  Depending on what you are talking about, it might be ◦ An atom of a single element ◦ A molecule of a substance ◦ A formula unit of an ionic compound

8.  The molar mass of a substance is the mass of one mole of a substance in grams.  To determine it, you must know the chemical formula for the substance, and the atomic masses for each of the elements in it.

9. MgCl 2  Each particle of this compound contains: ◦ 1 atom of Magnesium ◦ 2 atoms of chlorine  The molar mass of MgCl 2 = ◦ 1 x atomic mass of Mg plus ◦ 2 x atomic mass of Cl= ◦ 1x 24.305 g Mg / mole ◦ +2x35.453 g Cl / mole = 95.211 g/mol MgCl 2

10. Remember, the sum of the atomic masses times the number of atoms of each kind of element is equal to the mass of one mole of the substance. Examples: Na = 22.990 g/mol + Cl = 35.453 g/mol Therefore, NaCl has a molar mass of 58.4743 g/mol Nitric acid is HNO 3. Its molar mass is H = 1.008 x 1 = 1.008 g/mol N = 14.007 x 1 = 14.007 g/mol O = 15.999 x 3 = 47.997 g/mol Total = 63.012 g/mol HNO 3

11.  The subscripts in the formula tell you how many of each atom to include in your calculations  Ca 3 N 2 will have three Ca atoms and 2 N atoms  If there are parenthesis in a formula, remember that the number outside the parenthesis acts as a multiplier for everything within the parenthesis.  Mg(OH) 2 particles contain 1 Mg, 2 O and 2 H atoms per particle

12.  We use dimensional analysis to work with moles, grams and particles.  Atomic masses, one mole, and Avogadro’s number can be used as conversion factors to convert between moles, grams and particles of an element

13. Equals 1 mole of Nitrogen 6.022 x 10 23 atoms of Nitrogen 14.007 g of Nitrogen

14.  How many grams are there in 5.40 moles of Nitrogen?  Converting from MOLES to GRAMS The conversion factor you will use is: 1 mole N = 14.007 g N  5.40 moles N x 14.007 g N = 1 mole 75.6 g N

15.  How many atoms are there in 40.6 g Nitrogen?  Converting from GRAMS to ATOMS  The conversion factor that you will use is 14.007 g Nitrogen = 6.022 x 10 23 atoms  40.6 g N x 6.022 x 10 23 atoms = 14.007 g N 1.74 x 10 24 atoms of N

16.  How many moles are there in 2.3 x 10 23 atoms of Nitrogen?  Converting from ATOMS to MOLES  The conversion factor that you will use is: 1 mole Nitrogen = 6.022 x 10 23 atoms  2.3 x 10 23 atoms x 1 mole = 6.022 x 10 23 atoms 0.38 moles N

17.  Be sure to think about your setup when working on these problems (what units do you want to cancel out, what units do you want to get?  Round your significant figures based upon your starting point.  Use a two part label – units and substance ◦ For example “g CaCl 2 ” or “atoms H 2 O”