Hydrogen Bonding

Question 1

Hydrogen bonding is the strongest intermolecular force

Answer 1

Hydrogen bonding only happens when hydrogen is covalently bonded to fluorine nitrogen oxygen

Fluorine nitrogen and oxygen are very electronegative so they draw the bonding electrons away from the hydrogen atom

The hydrogen bond is so polarised and the hydrogen has such a high charge density because it’s so small that the hydrogen atoms

Organic molecules that form hydrogen bonds often contain the OH or NH groups

Question 2

Hydrogen bonds affect how a substance behaves

Answer 2

Substances that form hydrogen bonds have high melting and boiling points because a lot of energy is required to overcome these intermolecular forces

Question 3

The boiling point of group 7 hydrides

Answer 3

HF has the strongest intermolecular force therefore means has a very high boiling point

HCl To HI The permanent dipole dipole interactions decrease, the number of electrons in the molecule increases, so the strength of the London forces also increase. this affect overrides the decrease in the strength of permanent dipole permanent dipole interactions so the boiling point increases

Question 4

Solubility and hydrogen bonding

Answer 4

Substances that form hydrogen bonds are soluble in water

this is because they can form hydrogen bonds with water molecules allowing them to mix and dissolve

Question 5

Alcohols have higher boiling points than similar alkanes because…..

Answer 5

All alcohol is contain a polar OH group which helps alcohols form hydrogen bonds

Hydrogen bonding gives alcohols high boiling points compared to non-polar compounds

Question 6

Solubility part 2

Answer 6

For a substance to dissolve

bonds in the substance have to break bonds in the solvent have to break

New bonds have to be made between the substance and the solvent

Question 7

Polar solvents

Answer 7

They are made of polar molecules such as water meaning they can hydrogen bond with each other

Question 8

Non polar solvents

Answer 8

Such as hexane bond to each other by London forces

Question 9

Ionic substances dissolved in polar solvents

Answer 9

For example water

Water is a polar solvent

when an ionic substances mixed with water the ions in the ionic substance are attracted to the oppositely charged ends of the water molecules

Some ionic substances do not dissolve because the bonding between the ions are too strong

Question 10

Not all molecules are polar bonds dissolve in water

Answer 10

For example halogeonoalkanes contain polar bonds but the dipoles aren’t strong enough to form hydrogen bonds with water

The hydrogen bonds between water molecules are stronger than the bonds that would be formed to the halogenoalkanes therefore they do not dissolve

However they can form permanent dipole permanent dipole bonds therefore can dissolve in polar solvents that also form permanent dipole permanent dipole bonds

Question 11

Nonpolar substances

Answer 11

Nonpolar substances have London forces between the molecules. they form similar bonds with nonpolar solvents