Chemistry

Water

?Boiling point

X Y

have the same boiling point??

the difference of physical properties (boiling point, freezing point) based on

differences in intermolecular forces (van der Waals forces, London forces, and hydrogen

bonding).

There are three intermolecular forces

Let’s see

1. Which of the following has the lowest boiling point?O2 F2 Cl2

Quizz

2. Fill the blank below.Boiling point and freezing point of polar molecules are ….. than non polar molecules.Higher Lower

3. Which of the following has the highest boiling point?HI CH4 H2O

For non polar molecules, only intermolecular force of attraction is London force

London force stronger for larger molecules, weaker for smaller molecules

Which of the following has the lowest boiling point?O2 F2 Cl2

Atomic size decreases across a row (left to right). F is smaller than O. F2 is smaller than O2

Which of the following has the lowest boiling point?

O2 F2 Cl2

Atomic size increases going down a column. F is smaller than Cl. F2 smaller than Cl2

relative molecular mass >>

london force >>

Boiling point and freezing point increase

Pentane Butane>>Pentane Butane

Freezing point

– 129.8 °C (143 K)

−138.4 °C (135.4 K)

Boiling point 36.1 °C (308 K) −0.5 °C (272.6 K)

For polar molecules, not only intermolecular force of attraction is London force. There is dipole-dipole force.intermolecular force in polar molecules is stronger than intermolecular force in non polar molecules.

Boiling point and freezing point of polar molecules is higher than non polar molecules.

Freezing point Boiling point

relative molecular mass

Hydrogen bonding is much stronger than the van der Waals force.

Energy to break the hydrogen bond is about 15-40 kJ / mol while for the van der Waals force of about 2-20 kJ / mol.

That is why the substances that have a hydrogen bond has a higher freezing point, and boiling point

Higher boiling point is due to strongerintermolecular forces. Lower boiling pointis due to weaker intermolecular force.

A B C

Hydrogenbonding

Dipole-dipoleforce

Londonforce

Which one that have highest boiling point?1 s t 2n d 3 r d

H2O HI CH4

Hydrogenbonding

Dipole-dipoleforce

Londonforce

1 s t 2n d 3 r d

H2O HI CH4

Freezing point 0°C -83.5°C −138.4 °C

Boiling point 100 °C 19.5°C −0.5 °C