Chapter 19: Molecules Chapter 19: Molecules and Compoundsand Compounds

Section 19.3Section 19.3

Comparing Comparing MoleculesMolecules

COMPARING DIFFERENT COMPARING DIFFERENT MOLECULESMOLECULES

•How does the How does the mass of different mass of different

molecules molecules compare?compare?

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

of calcium carbonate?

Recall atomic mass Recall atomic mass units (amu)…units (amu)…

•Atoms are assigned a Atoms are assigned a ____________ __________ __________ on on carboncarbon as the as the standard.standard.•Known as Known as atomic mass unitatomic mass unit

6

CCarbon12.0107

24

19.3 Comparing 19.3 Comparing MoleculesMolecules

Chemical formula Chemical formula gives 3 pieces of info:gives 3 pieces of info:

–_____ / _______ of atoms._____ / _______ of atoms.– if ________ ions are if ________ ions are

present.present.– allows calculation of mass allows calculation of mass

of 1 molecule of a of 1 molecule of a compound relative to mass compound relative to mass of other compounds.of other compounds.

Formula MassFormula Mass

• Formula mass is determined Formula mass is determined by _____ up the atomic mass by _____ up the atomic mass unit (amu) of all the atoms in unit (amu) of all the atoms in the compound.the compound.

• The atomic masses are listed The atomic masses are listed on the ________ table.on the ________ table.

Example:Example: Figuring Figuring Formula MassFormula Mass

•HH22O means 2H and 1OO means 2H and 1O

• 2 (1.01 amu) =_____ 2 (1.01 amu) =_____ +1 (16.00 amu) = +1 (16.00 amu) = ________

•Formula massFormula mass = ____= ____amu of Hamu of H22OO

An amu is very small, An amu is very small, so to be usable in so to be usable in measurements, we measurements, we equate the equate the ______________ ____________ of the of the formulaformula massmass in in amuamu to an to an equalequal amountamount in in __________. .

Avogadro’s NumberAvogadro’s Number

• The formula mass in The formula mass in grams of any element or grams of any element or compound contains compound contains ____ ____ ____________ atoms or atoms or molecules.molecules.• Known as Avogadro’s # or Known as Avogadro’s # or

a a “____”“____” of the substance. of the substance.

So, how do we So, how do we use this value?use this value?

• If you measure out 100.09 If you measure out 100.09 grams of CaCOgrams of CaCO33, you have , you have 6.02 x 106.02 x 102323 molecules of molecules of CaCOCaCO33..• Likewise, 18.02 g of HLikewise, 18.02 g of H22O O

contains 6.02 x 10contains 6.02 x 102323 molecules molecules of water.of water.

Example: BaClExample: BaCl2 2 2H2H22OO

• 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) = 2 O = 2(16.00) = 32.0032.00 Formula mass = 244.24 Formula mass = 244.24 amuamu