Download - The Ties That Bind
The Ties That Bind
Chemical Bonding and Interactions
Chemical Bonding and Interactions1. Stable Electron Configurations2. Electron-Dot (Lewis) Structures
1. Drawing, Rules for Drawing2. The Octet Rule3. Some Exceptions to the Rule
3. Ionic Bonding1. Naming ionic compounds2. Drawing
4. Covalent Bonding1. Naming covalent compounds2. Drawing3. Electronegativity and Polar Covalent Compounds
5. Molecular Shapes and the VSEPR Theory6. Intermolecular Forces of Attraction
1. H-bonds, Dipole-Dipole, Ion-Dipole, London Dispersion Forces
INTERMOLECULAR FORCES OF ATTRACTION
A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary.
2 Phases
Solid phase - ice
Liquid phase - water
11.1
Intermolecular Forces
11.2
Intermolecular forces are attractive forces between molecules.
Intramolecular forces hold atoms together in a molecule.
Intermolecular vs Intramolecular
• 41 kJ to vaporize 1 mole of water (inter)
• 930 kJ to break all O-H bonds in 1 mole of water (intra)
Generally, intermolecular forces are much weaker than intramolecular forces.
“Measure” of intermolecular force
boiling point
melting point
Hvap
Hfus
Hsub
Intermolecular ForcesIntermolecular Forces
Intermolecular Forces
Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
11.2
Ion-Dipole Interaction
Intermolecular ForcesIntermolecular Forces
11.2
Intermolecular Forces
Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
11.2
Intermolecular ForcesIntermolecular Forces
Dipole-Dipole ForcesDipole-Dipole Forces There is a mix of attractive and
repulsive dipole-dipole forces as the molecules tumble.
If two molecules have about the same mass and size, then dipole-dipole forces increase with increasing polarity.
Intermolecular ForcesIntermolecular Forces
London Dispersion ForcesLondon Dispersion Forces Weakest of all intermolecular forces. It is possible for two adjacent neutral molecules to
affect each other. The nucleus of one molecule (or atom) attracts the
electrons of the adjacent molecule (or atom). For an instant, the electron clouds become distorted. In that instant a dipole is formed (called an
instantaneous dipole).
Intermolecular ForcesIntermolecular Forces
London Dispersion ForcesLondon Dispersion Forces
Intermolecular ForcesIntermolecular Forces
London Dispersion ForcesLondon Dispersion Forces One instantaneous dipole can induce another
instantaneous dipole in an adjacent molecule (or atom).
Instantaneous dipoles are called London Dispersion Forces.
Polarizability is the ease with which an electron cloud can be deformed.
The larger the molecule (the greater the number of electrons) the more polarizable.
Intermolecular ForcesIntermolecular Forces
London Dispersion ForcesLondon Dispersion Forces
Intermolecular ForcesIntermolecular Forces
London Dispersion ForcesLondon Dispersion Forces London dispersion forces increase as molecular weight
increases. London dispersion forces exist between all molecules. London dispersion forces depend on the shape of the
molecule. The greater the surface area available for contact, the
greater the dispersion forces. London dispersion forces between spherical molecules
are lower than between sausage-like molecules.
Intermolecular ForcesHydrogen Bond
11.2
The hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.
A H…B A H…Aor
A & B are N, O, or F
Hydrogen Bond
11.2
Intermolecular ForcesIntermolecular ForcesHydrogen BondingHydrogen Bonding Hydrogen bonds are responsible for:
Ice Floating Solids are usually more closely packed than liquids; therefore, solids are more dense than liquids. Ice is ordered with an open structure to optimize H-bonding. Therefore, ice is less dense than water. In water the H-O bond length is 1.0 Å. The O…H hydrogen bond length is 1.8 Å. Ice has waters arranged in an open, regular hexagon. Each + H points towards a lone pair on O. Ice floats, so it forms an insulating layer on top of lakes, rivers,
etc. Therefore, aquatic life can survive in winter.
Maximum Density40C
Ice is less dense than water
Density of Water
11.3
Water is a Unique Substance
Intermolecular ForcesIntermolecular ForcesHydrogen BondingHydrogen Bonding Hydrogen bonds are responsible for:
Protein Structure Protein folding is a consequence of H-
bonding. DNA Transport of Genetic Information
Intermolecular ForcesIntermolecular ForcesComparing Intermolecular ForcesComparing Intermolecular Forces
Properties of Liquids
Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area.
Strong intermolecular
forces
High surface tension
11.3
Some Properties of LiquidsSome Properties of Liquids
Surface TensionSurface Tension
Properties of Liquids
Cohesion is the intermolecular attraction between like molecules
11.3
Adhesion is an attraction between unlike molecules
Adhesion
Cohesion
Properties of Liquids
Viscosity is a measure of a fluid’s resistance to flow.
11.3
Strong intermolecular
forces
High viscosity
Ultrahydrophobic surfaces
PHASE CHANGES
We can use the concepts of intermolecular forces of attraction to explain the physical phase changes
Phase ChangesPhase Changes Surface molecules are only attracted inwards towards
the bulk molecules. Sublimation: solid gas. Vaporization: liquid gas. Melting or fusion: solid liquid. Deposition: gas solid. Condensation: gas liquid. Freezing: liquid solid.
Energy Changes Accompanying Phase ChangesEnergy Changes Accompanying Phase Changes Energy change of the system for the above processes
are:
Phase ChangesPhase Changes
Energy Changes Accompanying Phase ChangesEnergy Changes Accompanying Phase Changes All phase changes are possible under the right
conditions (e.g. water sublimes when snow disappears without forming puddles).
The sequence
heat solid melt heat liquid boil heat gas
is endothermic. The sequence
cool gas condense cool liquid freeze cool solid
is exothermic.
Phase ChangesPhase Changes
Energy Changes Accompanying Phase ChangesEnergy Changes Accompanying Phase Changes
Phase ChangesPhase Changes
Heating CurvesHeating Curves
Test yourself1. Which has a higher boiling point, ethane (C2H6) or dodecane (C12H26)?2. What kind of IFA will be present in the following
combinations/mixtures?1. Water and ammonia2. Octane and water3. CCl4 and CHCl34. Hydrofluoric acid (HF) and water?5. Acetic acid and cysteine? (see board for structures)6. Water and NaCl
3. Which has a higher boiling point, neopentane or n-pentane? (See board for structures)
4. Which will have a higher boiling point: 1. Ne or Xe2. N2 or Kr