Chapter 19: Molecules and Compounds Section 19.3 Comparing Molecules

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

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

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 Carbon 2424

19.3 Comparing Molecules

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.

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.

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

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 _____.

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.

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

Example: BaCl 2 2H 2 O 1 Ba = 1(137.30) = Ba = 1(137.30) = Cl = 2(35.45) = Cl = 2(35.45) = H = 4(1.01) = H = 4(1.01) = O = 2(16.00) = O = 2(16.00) = Formula mass = amu Formula mass = amu