Unit 2- Intermolecular forces

Question 1

Whar are Van der Waals forces?

Answer 1

• London forces e.g. temporary and induced dipole interactions and permanent dipole interaction

Question 2

How are dipoles created?

Answer 2

• Electrons are always moving
• At the instant where there are more electrons to one side of the molecule , a dipole is formed
• one end is slightly positive while the other slightly negative

Question 3

What are induced dipoles?

Answer 3

• When the temporary dipoles on one molecule affect another molecule
• The electrons will repel/attract the electrons causing an electron shift in the other molecule
• An induced dipole is formed

Question 4

Explain the strengths of dipoles?

Answer 4

• ​Greater number of electrons lead to a greater polarisability which increases the chances of a dipole
• Increase in surface area allows for a greater area where the VDW forces can act therefore greater strength
• Increases down the group due to a larger radius

Question 5

What is hydrogen bonding?

Answer 5

• When a hydrogen atom which is covalently bonded can form a intermolecular bond with an electronegative atom
• They are Oxygen, Fluorine and Iodine
• The hydrogen is slightly positive
• Acts in addition to VDW

Question 6

How does the boiling and melting temperature of an alkane vary?

Answer 6

• Increased chain length leads to stronger Intermolecule forces
• Due to an increased number of electrons
• Leads to a stronger attraction
• Branching decreases the melting temperature
• Due to less surface area

Question 7

Why is alcohol less volatile than alkanes?

Answer 7

• Alcohol forms Hydrogen bonds
• Alkanes have london forces
• Hydrogen bonds are stronger than london forces
• More energy is required to break the hydrogen bonds therefore making alcohol less volatile

Question 8

What are the trends in the melting and boiling temperature of the hydrogen halides?

Answer 8

• Includes HF, HCl, HBr and HI
• HF has the greatest temperature due to hydrogen bonding
• From HCl-HI, temperature increases
• Due to atomic radius increasing therefore a greater surface area
• Strgoner VDW forces

Question 9

What is soluble in water?

Answer 9

• Polar solids
• Polar organic substances
• Ionic compounds

Question 10

What is soluble in hexane?

Answer 10

• non polar solids

Question 11

What happens in polar and non polar liquids when ionic compounds and non-polar liquids are mixed?

Answer 11

• immisicible layer formed
• two layers can be seen