Transcript Bonding Notes

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 CO2 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: SrCl2 · 5H2O: 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: 23.00 + 35.45
– NH4OH: 14.01 + (4 x 1.008) +16.00 + 1.008
– Ca(NO3)2 40.08 + (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 16.00 =
– Total
22.99
14.01
48.00
85.00
• % 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.