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The Ties That Bind. Chemical Bonding and Interactions. Chemical Bonding and Interactions. Stable Electron Configurations Electron-Dot (Lewis) Structures Drawing, Rules for Drawing The Octet Rule Some Exceptions to the Rule Ionic Bonding Naming ionic compounds Drawing Covalent Bonding

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the ties that bind

The Ties That Bind

Chemical Bonding and Interactions

chemical bonding and interactions
Chemical Bonding and Interactions
  • Stable Electron Configurations
  • Electron-Dot (Lewis) Structures
    • Drawing, Rules for Drawing
    • The Octet Rule
    • Some Exceptions to the Rule
  • Ionic Bonding
    • Naming ionic compounds
    • Drawing
  • Covalent Bonding
    • Naming covalent compounds
    • Drawing
    • Electronegativity and Polar Covalent Compounds
  • Molecular Shapes and the VSEPR Theory
  • Intermolecular Forces of Attraction
    • H-bonds, Dipole-Dipole, Ion-Dipole, London Dispersion Forces
slide4

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

slide5

Generally, intermolecular forces are much weaker than intramolecular forces.

Intermolecular Forces

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)

“Measure” of intermolecular force

boiling point

melting point

DHvap

DHfus

DHsub

11.2

slide7

Ion-Dipole Interaction

Intermolecular Forces

Ion-Dipole Forces

Attractive forces between an ion and a polar molecule

11.2

slide10

Orientation of Polar Molecules in a Solid

Intermolecular Forces

Dipole-Dipole Forces

Attractive forces between polar molecules

11.2

slide11

Intermolecular Forces

Dipole-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.
slide12

Intermolecular Forces

London 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).
slide13

Intermolecular Forces

London Dispersion Forces

slide14

Intermolecular Forces

London 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.
slide15

Intermolecular Forces

London Dispersion Forces

slide16

Intermolecular Forces

London 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.
slide17

or

H

H

B

A

A

A

Intermolecular Forces

Hydrogen Bond

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 & B are N, O, or F

11.2

slide19

Intermolecular Forces

Hydrogen 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.
slide20

Maximum Density

40C

Ice is less dense than water

Water is a Unique Substance

Density of Water

11.3

slide22

Intermolecular Forces

Hydrogen Bonding

  • Hydrogen bonds are responsible for:
    • Protein Structure
      • Protein folding is a consequence of H-bonding.
      • DNA Transport of Genetic Information
slide23

Intermolecular Forces

Comparing Intermolecular Forces

slide24

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

slide26

Adhesion

Cohesion

Properties of Liquids

Cohesion is the intermolecular attraction between like molecules

Adhesion is an attraction between unlike molecules

11.3

slide27

Properties of Liquids

Viscosity is a measure of a fluid’s resistance to flow.

Strong intermolecular forces

High viscosity

11.3

phase changes
PHASE CHANGES
  • We can use the concepts of intermolecular forces of attraction to explain the physical phase changes
slide31

Phase 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 Changes

  • Energy change of the system for the above processes are:
slide32

Phase Changes

Energy 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.

slide33

Phase Changes

Energy Changes Accompanying Phase Changes

slide34

Phase Changes

Heating Curves

test yourself
Test yourself
  • Which has a higher boiling point, ethane (C2H6) or dodecane (C12H26)?
  • What kind of IFA will be present in the following combinations/mixtures?
    • Water and ammonia
    • Octane and water
    • CCl4 and CHCl3
    • Hydrofluoric acid (HF) and water?
    • Acetic acid and cysteine? (see board for structures)
    • Water and NaCl
  • Which has a higher boiling point, neopentane or n-pentane? (See board for structures)
  • Which will have a higher boiling point:
    • Ne or Xe
    • N2 or Kr