1 Molecular and Formula Mass What is the relative atomic mass of the following atoms? (Always to TWO decimal places!) Oxygen Zinc Iron Silver Calcium

2 Molecular Mass (Covalent) This is the mass of one molecule expressed in unified atomic mass units (u) It is calculated by adding up the average atomic mass of each atom found in a compound

3 Calculate the molecular mass of H 2 O. mass of H 2 O = 2 H + 1 O = (2 x 1.01 u) + (1 x u) = u Practice 1 Calculate the molecular mass of C 3 H 8. mass of C 3 H 8 = (3 x u) + (8 x 1.01 u) = u

4 Formula Mass (Ionic) Since ionic compounds do not actually consist of individual atoms, the mass is referred to as formula mass This is the total mass of each atom written in the formula for an ionic compound expressed in unified atomic mass units (u)

5 Calculate the formula mass of MgO. mass of MgO = 1 Mg + 1 O = (1 x 24.31u) + (1 x 16.00u) = u Practice 2 Calculate the formula mass of CaCl 2. mass of CaCl 2 = (1 x u) + (2 x u) = u

6 Houston! We have a problem! How can you measure u? We do not have an electronic scale which can measure in u, only g, kg or lb. If we use a beam balance scale we would have to use carbon atoms as the mass standards.

7 Introducing the MOLE and Molar Mass In 1811, a chemist named Amedeo Avogadro realized that any convenient quantity of matter must contain an enormous number of chemical entities.

8 Josef Loschmidt latter showed that approx , or 6.02 x atoms was a convenient and measurable number of entities to work with.

x This number is called Avogadro’s constant ( N A ) One mole of an entity has 6.02 x entities in it. 1 mole = 6.02 x entities The symbol for mole is ‘ n ’

10 Why 6.02 x ? Many experiments have shown that 6.02 x atoms of an element has approx. the same mass in grams, g, as the relative atomic mass in unified atomic mass units, u. ElementAtomic Mass (u) Molar Mass ( g ) mol Argon39.95 u39.95 ( g ) mol Carbon12.01 u12.01 ( g ) mol

11 Molar Mass is the mass, in grams per mole, of one mole of a substance. The SI unit for molar mass is g mol The SI symbol for molar mass is “M”. Example: The mass of an ammonia molecule is u The mass of one mole of ammonia molecules is g

12 How large is 6.02 x ? One mole of pennies would make at least seven stacks that would reach the moon. One mole of TimBits would cover the Earth and be 8 kilometers deep. Astronomers estimate that there is a mole of stars in the Universe.

13 How large is 6.02 x ? One mole of marshmallows would cover the USA to a depth of kilometers. One mole of high school textbooks would cover the USA to a depth of 300 kilometers.

14 How large is 6.02 x ? If you spent $ 6.02 x10 23 at a rate of $1.00 per second, how long in years would the money last? Assume that every year has 365 days.

15 Practice 3 What is the molecular mass of glucose? u What is the molar mass of glucose? g/mol What is the mass of 1 mole of table salt? g What is the mass of 3 moles of table salt? g

16 Textbook Reference pp Assigned Questions p. 168 Practice UC # 1, 2, 4, 5, 6 p. 170 Practice UC # 7, 8, 9, 10, 11, 12, 13 p. 172 Practice UC # 1, 2, 3, 4 p. 173 Practice UC # 5, 6, 7, 8 pp. 176 – 177 Practice UC (a) and (b) ONLY from # 9, 10, 11, 12