Quiz What is an electrostatic dipole. In one or two sentences describe permanent dipole. What’s the difference between polar and non-polar molecules? In one or two sentences describe temporary dipole.

Quiz 1. Electrostatic dipole is a slight positive or negative charge on an atom in a molecule. 2. Permanent dipole is when one part of the molecule will always have a partial positive or negative charge. 3. Polar molecules have permanent dipoles whereas non-polar molecules only have temporary dipoles. 4. Temporary dipole has uneven-distribution of electron density in a very short time frame causing a slight positive region a slightly negative region.

Hydrogen Bonding AIM – to investigate the effect of hydrogen bonding on the properties of molecular substances

If you plot the boiling points of the compounds of the Group 4 elements with hydrogen, you find that the boiling points increase as you go down the group. This is what you would expect considering Van der Waals forces

Repeating this exercise with compounds of the elements in Groups 5, 6 and 7 with hydrogen gives odd results. the boiling point of the first element in each group is higher than expected

For NH3, H2O and HF there must be some additional intermolecular forces of attraction, requiring more heat energy to break. These relatively powerful intermolecular forces are called hydrogen bonds.

In each of these molecules the hydrogen is attached to a very electronegative element. This causes the hydrogen to acquire a significant amount of positive charge. Each of the elements to which the hydrogen is attached is significantly negative and also has at least one "active" lone pair.

Hydrogen bonding in water The δ+ hydrogen is so strongly attracted to the lone pair that it is almost as if you were beginning to form a covalent bond. The attraction is significantly stronger than an ordinary dipole-dipole interaction. Hydrogen bonds have about 1/10 of the strength of an average covalent bond, and are being constantly broken and reformed in liquid water.

Hydrogen bonding notes Most trends in melting and boiling point of molecular substances can be explained by the strength of temporary and permanent dipoles.   Compounds containing hydrogen bonded to fluorine, nitrogen or oxygen will have unusually high boiling and melting points. This is because F, O and N are very electronegative when bonded with hydrogen the partial –ve and +ve charges are big, therefore stronger attraction between molecules.

Year 13 Literacy Exercise Polarity of Molecules Write a paragraph to explain the following statement: “CCl4 does not have a permanent dipole moment but CH3Cl does.”   Use the following terms in your answer Electronegativity, Symmetrical, Cancel out, Polar bonds Non-polar bonds, Tetrahedral, Permanent dipole, Non-polar molecule

Complete investigation 7.1 on page 176 of textbook Complete test yourself 7D Complete review questions for chapter 6 Write down on a piece of paper areas from the last 3 chapters that you would like to review for revision tomorrow 5. End of unit test sometime soon.