Bonding

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

Bonding Ionic – Between metals and nonmetals or polyatomic ions – Transfer of electrons Covalent – Between nonmetals – Electrons shared 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.

Dipole moment Refers to a bond between two atoms Is a vector that points to the more electronegative element Its magnitude is the mathematical difference between the two electronegativities Example: for a nitrogen oxygen bond, the eneg for nitrogen is 3.0 and the eneg for oxygen is 3.5. the dipole moment will point to oxygen and have a magnitude of 0.5

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 (N, O, F) London dispersion forces: an attraction between instantaneously induced dipoles (occurs in nonpolar substances like CO 2 and atomic substances like Ar) Dipole dipole interactions: attractions between polar molecules

Hydrates Water is chemically associated Anhydrous: without the water. Molar mass: – Do first part as normal, thenadd the number of waters – Example: SrCl 2 · 5H 2 O: Sr + 2 Cls + 5 waters, or (88) + (2 x 35) + (5 x 18) Uses: – Disposable diapers, antiperspirants, moisture indicator strips

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, multiply 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.