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Supporting Year 12 and 13 chemists at The Cavendish School in Hemel Hempstead
Markschemes for exam papers
Work from Wednesday's Year 12 lesson (5th March)
Revision resources
Work from recent lessons
Past A2 exam papers
Past AS exam papers
Links to Alevel Chemistry tick lists
AS and A2 Chemistry exam dates
AS exams: Wed, 4th Jun 2008
A2 exams (Unit 2849 retake): Thurs, 12th Jun 2008
A2 exams (Unit 2854): Thurs, 19th Jun 2008
A2 exams (Unit 2849 retake): Thurs, 12th Jun 2008
A2 exams (Unit 2854): Thurs, 19th Jun 2008
9 comments:
WELL DONE, Tom, for being the only person to do your homework!!! The volatility of a liquid is how easily it changes into a gas or vapour.
:)...and the volatility of the halogens decreases as you go down the group! This is because the melting and boiling points increase.
THIS is due to the fact that as the diatomic molecules increase in size down the group, there are more electrons present ro induce dipoles and create van der Waals forces of attraction. The larger the molecule, the more electrons, the stronger the intermolecular forces of attraction, the more energy required to change their state - thus the melting and boiling points increase down the group.
'Their' state was rather ambiguous... I meant the state of the substance in question...
Fantastic additions to Tom's original posts, Carina and Rosy! Well done.
To add to your understanding...
- What is a DIPOLE?
- What is meant by INDUCED DIPOLES? Why do they occur?
- What are the 3 main types of INTERMOLECULAR FORCES and how do these vary in strength?
(These are ideas that you will be coming across with Miss Bendle in 'The Polymer Revolution' if you haven't already done so.)
A dipole is when a molecule/part of a molecule has an imbalanced charge (i.e.: positive end/s and negative end/s).
An induced dipole occurs when a non-polar molecule is near a polarised molecule; the negatively charged part of the latter causes repulsion and thus movement of the electron cloud of the non-polar molecule, giving it an imbalanced charge, which in this case is called an induced dipole.
3 types of intermolecular forces:
Permanent Dipole-Permanent Dipole
Permanent Dipole-Induced Dipole
Instantaneous Dipole-Induced Dipole (also called Van der Waals forces, London forces or Dispersion forces).
Unless the answer to that question is ionic interactions, dipole-dipole interactions and hydrogen bonding, in which case I have confused myself!
Well done, Carina! You have shown a great understanding of dipoles and intermolecular forces.
Any offers from anyone else on the answer to Carina's question on what the 3 types of intermolecular forces are?
Any thinking some more about dipoles: Carina is correct in her definition of a dipole but what is it that CAUSES the molecule to have a slightly positive end and a slightly negative end?
It is the position of electrons that causes the molecule to have a slightly positive and slightly negative end.
Instantaneous dipoles are caused in a split second chance due to the random movement of electrons.
Permanent dipoles are called polar molecules; each end has substantially different electro-negativity.
Induced dipoles are caused by the 'domino' effect of an instantaneous or permanent dipole.
Brilliant, Sam! An excellent description of dipoles - well done!
So what is it that affects the position of electrons in a bond, i.e. so that they are closer to one of the elements in that bond than the other?
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