2. Quantitative Chemistry Moles

3. Molecule vs. Ionic Compound Molecules Molecules Covalently bonded (share electrons) Covalently bonded (share electrons) Non-repeating units Non-repeating units Representative Unit: MOLECULE Representative Unit: MOLECULE Neutral Molecules Neutral Molecules Ionic Compounds (lose/gain electrons) Ionic Compounds (lose/gain electrons) Repeating units (NaCl really Na x Cl x ) Repeating units (NaCl really Na x Cl x ) Representative Unit: FORMULA UNIT Representative Unit: FORMULA UNIT Positive & Negative Ions form Neutral compound Positive & Negative Ions form Neutral compound

4. Molecular vs. Formula Mass Molecules can be accurately represented by the molecular mass: Molecules can be accurately represented by the molecular mass: H 2 O = 18.015 amu Ionic (crystalline) compounds cannot – WHY? NaCl = ?

5. AMU to GRAMS Atomic Mass Copper Atomic Mass Copper Cu = 63.546 amu How many atoms needed so the measured mass is equal to this value? 63.546 grams There lies the concept of the MOLE!

6. AMU to MASS Equal number of atoms of each as long as the ratio of atomic masses remained constant # of atoms Mass of C-12Mass of N-14Ratio of C to N masses 1 12 amu 14 amu1 : 1.167 6.02 x 10 23 (1 mole) 12 g14 g1 : 1.167 This means there are 6.02 x 10 23 atoms in EVERY ATOMIC MASS value when expressed in grams !

7. Remember … Molecular Mass is used for molecules And is expressed in AMU’s Formula Mass is used for Crystalline (ionic) compounds and is also expressed in AMU’s If we express an element or compounds mass in grams It is called … The Gram Molecular Mass or the Gram Formula Mass