Polarity+and+Intermolecular+Forces
Page 1: Polarity and Intermolecular Forces
Introduction to the concepts of polarity and their role in intermolecular forces.
Page 2: Charged Wands and Water Interaction
Summary:
Rubbing two different materials causes some electrons to transfer.
This results in static electricity; one material has a positive charge, and the other has a negative charge.
Water is deflected by positively charged glass wands and negatively charged plastic wands due to its polar nature.
Page 3: Water as a Polar Molecule
Water molecules display partial charges indicated by delta symbols (+ or -).
This symbolizes the asymmetric distribution of electrons in chemical bonds influencing polarity.
Page 4: Water Molecules and Charged Wands
Charged wands influence the orientation of water molecules:
Water molecules align their positive sides towards the charged wand.
Page 5: Intermolecular Forces
Partial Charges and Attractions:
Partial charges facilitate attractions between molecules, termed intermolecular forces (IMFs).
The term “inter” refers to “between.”
These forces arise due to the strength of polarity in the molecules.
Page 6: Natural Occurrences of IMF
Observation #1:
Water beads on waxed paper, while oil spreads out.
Observation #2:
Compounds of similar molecular mass can differ in state: Water (liquid at room temperature) versus Methane (gas).
Page 7: Polarity of Bonds
Electronegativity:
Covalent bonds can be nonpolar (equal sharing of electrons) or polar (unequal sharing of electrons).
Page 8: Determining Bond Polarity
Electronegativity Values:
H = 2.2, C = 2.6, O = 3.4.
Calculate differences to identify bond polarity.
Page 9: Electronegativity Differences
Differences determined:
C and H: 0.4 → Nonpolar covalent bond.
C and O: 0.8 → Polar covalent bond.
Page 10: Electronegativity Table
Summary of various molecular bonds and respective polarities based on electronegativity values.
Page 11: Summary of IMFs
Intermolecular forces describe the attractions between molecules.
Differences in electronegativity lead to uneven electron distribution, resulting in partial charges and dipoles.
Page 13: Calculation Exercise
Do Now: Fill out the polarity scale using electronegativity differences and calculate differences for specific bonds (N2, HF, NO, FCl).
Page 14: Bond vs. Molecular Polarity
Bond Polarity: The polarity of individual bonds.
Molecular Polarity: More critical, understands total electron distribution across the molecule.
Page 15: Diatomic and Polyatomic Molecules
Diatomic molecules are polar if bonded by a polar bond.
Polyatomic molecules require geometry examination to determine polarity.
Page 16: Molecular Geometry and Polarity
Different geometries (e.g., linear, trigonal planar, bent) affect molecular polarity distinctions in identical vs. non-identical bonded atoms.
Page 18: Inter- vs. Intra-Molecular Forces
Intramolecular Forces (within): Strong forces like ionic and covalent bonds.
Intermolecular Forces (between): Weaker forces that occur between molecules.
Page 20: Types of Intermolecular Forces
Types:
London Dispersion Forces
Dipole-Dipole Forces (including Hydrogen bonding)
Ion-Dipole Forces
Page 21: London Dispersion Forces
Present in all molecules and noble gas atoms; weakest form of IMF, relies on induced dipoles.
Page 22: Example of London Dispersion Forces
In Br2, the electron distribution can shift, creating temporary dipoles.
Page 23: Dipole-Dipole Forces
Occur only in polar molecules; larger polarity leads to stronger attractions.
Page 25: Hydrogen Bonding
A strong type of dipole-dipole interaction involving H and electronegative atoms (O, N, F).
Page 27: Ion-Dipole Forces
Strongest intermolecular forces occurring when ionic compounds mix with polar liquids like H2O.