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Bonding & Molecular Structure. Physical Science K Warne. Atoms and molecules (simple and giant ). H. H. H. O. O. O.  -.  -.  -. +. +. +. H. H. H. Intermolecular forces. Two different types of bonds occur in water. Intramolecular

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bonding molecular structure

Bonding & Molecular Structure

Physical Science

K Warne

intermolecular forces

H

H

H

O

O

O

-

-

-

+

+

+

H

H

H

Intermolecular forces
  • Two different types of bonds occur in water.
  • Intramolecular
    • Between hydrogen atoms and oxygen atomsinside the molecules Covalent bonds
  • Intermolecular
    • Betweentwo different water molecules Hydrogen bonds
bond polarity in water

H

-

O

+

H

Bond Polarity in Water

The oxygen atom has greater electronegativity so it is surrounded by greater electron density than the hydrogen atoms.

+

H

-

O

H

+

-

+

The water molecule is a

DIPOLE - it has two oppositely charged “poles”.

hydrogen bonding

H

H

H

O

O

O

-

-

-

+

+

+

H

H

H

Hydrogen Bonding

Example:

Water

  • The oppositely charged poles on the water molecules attract each other.
  • This electrostatic attraction constitutes Hydrogen bonding.
  • It is the strongest form of intermolecular attraction.
  • Hydrogen bonding exists only between molecules in which hydrogen is bonded to a very electronegative atom (H-O-X, H-NX2 or H-F).
  • Result in abnormally high boiling points.
molecular solids
Molecular solids

Strong covalent bonds

Iodine - I2

  • PROPERTIES
  • Low melting points
  • Brittle
  • Soluble in non-polar solvents
  • Non - conducting

Weaker intermolecular bonds

Covalently bonded molecules held together by weaker intermolecular bonding.

imf vs mp bp

. .

: X .

. .

. .

: X .

. .

IMF vs Mp & Bp

Mp & Bp increases with SIZE

and molecule MASS

density
Density
  • Density = mass/volume (g.cm-3)

1cm x 1cm x 1cm = 1cm3

Low density – gases

Few particles per cm3

High density – solids

Many particles per cm3

effect of temp
Effect of Temp
  • Temperature is a measure of average kinetic energy.
  • As temperature rises more particles have high energy.

Maxwell-Boltzman Curve

Average Ek Increases

effect of temp1
Effect of Temp

Maxwell-Boltzman Curve

  • Temperature is a measure of average kinetic energy.
  • As temperature rises – particles move faster – and further apart – substances expand – used in a thermometer.

Average Ek

viscosity
Viscosity
  • Viscosity is a measure of how thick (viscous) and sticky a liquid is.
  • Viscosity reduces the ability of a liquid to flow.
  • Liquids that flow readily (water) have a low viscosity.
  • Viscosity is a function of (depends on) the attractive forces of the molecules of the liquid.
  • Strong forces – high viscosity
  • Temperature also greatly affects viscosity: as temperature increases, viscosity decreases.

Kinetic energy enables particles to overcome forces.