CH2 - Bonding (2)
- Created by: beth-marie2511
- Created on: 01-06-16 19:02
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- CH2 - Bonding (2)
- The Influence of Hydrogen Bonding on Water Solubility
- For a compound to be water soluble it must be able to disrupt the hydrogen bonds between water molecules.
- It has to be able to form attractions with water molecules that are at least s strong as the hydrogen bonds between the water molecules.
- Ionic compounds are water soluble.
- They dissolve in water because the positive ions are attracted to the (delta -) negative O of the polar water molecules.
- And the positive ions are attracted to the (delta +) positive H of the polar water molecules.
- They dissolve in water because the positive ions are attracted to the (delta -) negative O of the polar water molecules.
- Other substances that are soluble in water includes those that can form hydrogen bonds themselves. E.G. Ethanol.
- Why are hydrocarbons insoluble (immiscible) in water?
- They are non-polar molecules.
- They are unable to disrupt hydrogen bonds.
- They have(e.g. octane) ID - ID bonds that are very weak compared to hydrogen bonds.
- What happens to the solubility of alcohols as the carbon chain gets longer?
- Solubility decreases.
- This is because the carbon chain is non-polar.
- Solubility decreases.
- For a compound to be water soluble it must be able to disrupt the hydrogen bonds between water molecules.
- Shapes of Molecules
- The number of electron pairs surrounding the central atom determines the shape of the molecule.
- Electron pairs repel each other in order to become as far apart as possible so that repulsion is minimised.
- Repulsion decreases in this order:
- Lone pair - Lone pair
- Lone pair - bonding pair
- Bonding pair - Bonding pair
- Lone pair - bonding pair
- Lone pair - Lone pair
- The Valence Shell Electron Pair Repulsion Theory allows us to predict the shapes of simple molecules and ions.
- Summary
- 1. Find the group number of the central atom. This is the number of electrons it contributes.
- 2. Count the atoms that surround the central atom - they each contribute one electron.
- 3. Subtract one electron for each positive charge / add one electron for each negative charge.
- 4. Divide by 2 to give the number of electron pairs that surround the central atom.
- 5. Take lone pairs of electrons into account..
- These cause bond angles to become smaller as bonds get pushed together.
- 6.. There is greatest repulsion between two lone pairs than two bonding pairs.
- The Influence of Hydrogen Bonding on Water Solubility
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