1. Chapter 19: Molecules and Compounds Section 19.3 Comparing Molecules

2. COMPARING DIFFERENT MOLECULES How does the mass of different molecules compare?How does the mass of different molecules compare?

3. Do you think that a molecule of water has the same mass as a molecule of calcium carbonate?

4. Recall atomic mass units (amu)… Atoms are assigned a ______ _____ _____ on carbon as the standard.Atoms are assigned a ______ _____ _____ on carbon as the standard. Known as atomic mass unitKnown as atomic mass unit 6 C Carbon 12.0107 Carbon 2424

5. 19.3 Comparing Molecules

7. Chemical formula gives 3 pieces of info: –_____ / _______ of atoms. –if ________ ions are present. –allows calculation of mass of 1 molecule of a compound relative to mass of other compounds.

8. Formula Mass Formula mass is determined by _____ up the atomic mass unit (amu) of all the atoms in the compound.Formula mass is determined by _____ up the atomic mass unit (amu) of all the atoms in the compound. The atomic masses are listed on the ________ table.The atomic masses are listed on the ________ table.

10. Example: Figuring Formula Mass H 2 O means 2H and 1OH 2 O means 2H and 1O 2 (1.01 amu) =_____ +1 (16.00 amu) = ____ 2 (1.01 amu) =_____ +1 (16.00 amu) = ____ Formula mass = ____ amu of H 2 OFormula mass = ____ amu of H 2 O

12. An amu is very small, so to be usable in measurements, we equate the _______ ______ of the formula mass in amu to an equal amount in _____.

13. Avogadro’s Number The formula mass in grams of any element or compound contains ____ ______ atoms or molecules.The formula mass in grams of any element or compound contains ____ ______ atoms or molecules. Known as Avogadro’s # or a “____” of the substance.Known as Avogadro’s # or a “____” of the substance.

14. So, how do we use this value? If you measure out 100.09 grams of CaCO 3, you have 6.02 x 10 23 molecules of CaCO 3.If you measure out 100.09 grams of CaCO 3, you have 6.02 x 10 23 molecules of CaCO 3. Likewise, 18.02 g of H 2 O contains 6.02 x 10 23 molecules of water.Likewise, 18.02 g of H 2 O contains 6.02 x 10 23 molecules of water.

15. Example: BaCl 2 2H 2 O 1 Ba = 1(137.30) = 137.301 Ba = 1(137.30) = 137.30 2 Cl = 2(35.45) = 70.902 Cl = 2(35.45) = 70.90 4 H = 4(1.01) = 4.044 H = 4(1.01) = 4.04 2 O = 2(16.00) = 32.002 O = 2(16.00) = 32.00 Formula mass = 244.24 amu Formula mass = 244.24 amu