which of these molecules has a permanent dipole (H2O, CO2, CCl4, NH3) which of these molecules has a permanent dipole (H2O, CO2, CCl4, NH3).Also state: shapes, angles and identify any polar bonds.

1) Choose a board (eg. 1,2 3 or 4) 2)Deduce the shape and angles of the molecules on the board. Also, identify polar bonds and polar molecules.

Intermolecular forces L.O.: Dipole-dipole London forces H-bonding

Permanent dipole–dipole forces between HCl molecules

A permanent dipole-dipole force is a weak attractive force between permanent dipoles in neighbouring polar molecules.

Induced dipole-dipole interactions (London forces)

The more electrons in each molecule, the stronger the attractive forces between the molecules.

Why do the boiling points of the noble gases increase as the atomic number of the noble gases increase?

Hydrogen bonding Describe hydrogen bonding between molecules containing –OH , –NH groups or F. Describe and explain the anomalous properties of water resulting from hydrogen bonding.

Look at this example of hydrogen bonding between 2 molecules of water. In pairs discuss: What is a hydrogen bond? What is required to make a hydrogen bond?

Hydrogen bonding: a type of intermolecular force in which a hydrogen atom covalently bonded to an electronegative atom interacts with another electronegative atom.

To form a hydrogen bonding we must have: a hydrogen atom that is bonded to a very electronegative atom (O,N and F). A very electronegative atom with a lone pair of electrons.

What trend would you expect in the boiling points of: Ne, Ar, Kr, Xe CH4, SiH4, GeH4, SnH4, NH3, PH3, AsH3, SbH3, HF, HCl, HBr HI H2O, H2S, H2Se, H2Te,

BOILING POINTS OF HYDRIDES Mr BOILING POINT / C° 100 -160 140 50 GROUP IV The boiling points of the hydrides increase with molecular mass. CH4 has the lowest boiling point as it is the smallest molecule. PbH4 GeH4 SiH4 Larger molecules have greater intermolecular forces and therefore higher boiling points CH4

BOILING POINTS OF HYDRIDES Mr BOILING POINT / C° 100 -160 140 50 GROUP V NH3 has a higher boiling point than expected for its molecular mass. There must be an additional intermolecular force. NH3

BOILING POINTS OF HYDRIDES Mr BOILING POINT / C° 100 -160 140 50 H2O GROUP VI H2O has a very much higher boiling point for its molecular mass. There must be an additional intermolecular force.

BOILING POINTS OF HYDRIDES Mr BOILING POINT / C° 100 -160 140 50 GROUP VII HF has a higher boiling point than expected for its molecular mass. There must be an additional intermolecular force. HF

BOILING POINTS OF HYDRIDES Mr BOILING POINT / C° 100 -160 140 50 H2O The higher than expected boiling points of NH3, H2O and HF are due to intermolecular HYDROGEN BONDING HF NH3 GROUP IV GROUP V GROUP VI GROUP VII

BOILING POINTS OF HYDRIDES Mr BOILING POINT / C° 100 -160 140 50 GROUP IV GROUP V GROUP VI GROUP VII

The boiling points of H2O, HF, NH3, are higher than what we would expect if only London forces were operating. This is because hydrogen bonding is present between the molecules in each of these compounds.

HYDROGEN BONDING - ICE each water molecule is hydrogen-bonded to 4 others in a tetrahedral formation ice has a “diamond-like” structure volume is larger than the liquid making it when ice melts, the structure collapses slightly and the molecules come closer; they then move a little further apart as they get more energy as they warm up this is why… water has a maximum density at 4°C ice floats. hydrogen bonding lone pair

HYDROGEN BONDING - ICE hydrogen bonding

Liquid water: hydrogen bonds break and reform Ice: water molecules are in fixed positions. Molecules are slightly less packed than in liquid water. Less dense then floats, then it forms at the top rather than in the bottom of lakes.

Hydrogen bonding in water

Draw H-bonding between: Group 1: a) 2 molecules of H2O b) 2 molecules of CH3OH, Group 2: 2 molecules of NH3 Group 3: 2 molecules of Me2NH Group 4: 1 molecule of H2O and CH3COCH3 Group 5: 2 molecules of CH3CO2H

In which of the following does hydrogen bonding not occur between molecules: H2O, NH3, HBr, HF Explain why hydrogen bonds do not form between a) molecules of CH4 b) molecules of CCl4 Explain why water molecules form on average two hydrogen bonds per molecule, where the ammonia molecule, NH3, forms only one 1)HBr

For H-bonding look out for O-H, N-H bonds or F

The ice lattice is an open network of H2O molecules

In DNA, three hydrogen bonds link C and G

In DNA, two hydrogen bonds link A and T

Double helix in DNA

Explain why the molecule PH3 has a pyramidal shape and a bond angle of 107o (3 or 4 marks) 4 electron pairs surround the central atom. 3 bonding pairs and a lone pair electron pairs repel other electron pairs lone pair repel more electron pairs get as far apart as possible