Bonding

Bonding and attractions Bonding – Sharing or transfer of electrons Attractions – Negativity of one atom/molecule attracted to positivity of another atom/molecule

Bonding Ionic – Between metals and nonmetals or polyatomic ions – Transfer of electrons – The strongest Covalent – Between nonmetals – Electrons shared – Weaker than ionic Metallic – Among metals – Sea of electrons model

Polar and nonpolar If electrons are shared evenly, the bond is nonpolar. If electrons are shared unevenly, the bond is polar Determine this by electronegativity difference Dipole moment is vector of electronegativity difference. It points toward the more electronegative.

Compounds Ionic compounds form formula units and have an empirical formula Covalent compounds form molecules and have a molecular formula

Intermolecular Attractions Hydrogen bonding: strong dipole dipole interactions in which hydrogen is attracted to a highly electronegative atom London dispersion forces: an attraction between instantaneously induced dipoles Dipole dipole interactions: attractions between polar molecules

Molar mass Molar masses, atomic weights/masses, molecular weights/masses, formula weights/masses: all mean the same Calculate by adding the atomic masses of every atom in the formula – NaCl: – NH 4 OH: (4 x 1.008) – Ca(NO 3 ) (2 x 14.01) + (6 x 16.00)

Percent composition Mass of what you are talking about divided by mass of molecule Example: percent nitrogen in sodium nitrate – Na: – N: – O: 3 x = – Total % N is (14.01/85.00) x 100 = 16.5%

Empirical formulas Lowest ratio of subscripts Note how to calculate empirical formulas – Convert % to g – Divide each by its molar mass – Divide each by smallest – Results should be whole number +/- 0.2 – If a result rounds to X.5, multiple each subscript by 2

Molecular formulas A whole number “multiple” of an empirical formula Divide given molar mass by empirical formula’s molar mass Multiply each subscript by this value.