Chemical Bonding revised

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6

Each water molecule is hydrogen bonded to four other water molecules

The water molecules in ice are farther apart than in liquid water, therefore ice is less dense than liquid water**

Hydrogen bonds are the strongest in the form shown in the next diagram

Slide 52

Slide 53

Unique Properties Reading

Read the handout on the unique properties of water

Slide 54

London Dispersion Forces

Dispersion forces act between all molecules, but in non-polar molecules they are the only force

Even though there are no permanent dipoles in non-polar molecules, it is possible to induce dipoles

Slide 55

Slide 56

Non-polar molecules also spontaneously form temporary dipoles

Electrons are in constant, rapid motion

For a brief moment the electron distribution can be uneven

This can form a positive pole and a negative pole in the molecule

Slide 57

The temporary dipole in the molecule can induce a temporary dipole in the next molecule, like the balloon and the wall

The process disperses through the substance

Slide 58

Factors Affecting Magnitude

Two factors affect LD forces:

Increased electrons = increased probability of a temporary dipole forming

Linear shapes have greater London dispersion forces

Slide 59

Structures and Properties of Compounds

The state of a substance (solid, liquid or gas) depends on the strength of the intermolecular forces

As particles gain kinetic energy (heat) they break their intermolecular bonds and change state

Slide 60

Time of Hydrogen Bonding

FYI – hydrogen bonds in liquid water break and reform 100 000 000 000 (1011) times every second

Slide 61

Melting and Boiling Points

Melting and boiling points of ionic substances and metals are about the same magnitude

Melting and boiling points of molecular substances are much lower

What does that tell us about the forces?

Slide 62

Ionic bonds are much stronger if the ions have a large charge