13.1 - Halogenoalkanes intro

Question 1

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Halogenoalkanes reactivity of the C-X bond (2 factors):

Answer 1

• C-X bond polarity
• C-X bond enthalpy

Question 2

B.P of halogenoalkanes (what does it depend upon, and when does it increase):

Answer 2

• depends upon the no. of carbon and halogen atoms
• b.p increases with increased chain length
  –>increases going down the halogen group

Question 3

Bond polarity of Halogenoalkanes:

Answer 3

• halogens are more electronegative than carbon
• bonds get less polar as you go down group 7

Question 4

Solubility of halogenoalkanes (polarity of them in water, IMF forces present, mixture of halogenoalkanes with hydrocarbons):

Answer 4

• polar C-X bonds aren’t polar enough to make the halogenoalkanes soluble in water
• main IMF bonds are dipole-dipole attractions and VDW forces
• halogenoalkanes mix with hydrocarbons so they can be used as dry-cleaning fluids and to remove oily stains

Question 5

Bond Polarity (nucleophiles):

Answer 5

nucleophiles attack electron deficient atoms (carbon)

Question 6

Bond enthalpy of halogenoalkanes (strength of bonds going down the group and why, which bonds are the most reactive?):

Answer 6

• bonds get weaker going down the group
  –>fluorine is the smallest atom of the halogens and the shared electrons in the C-F bond are strongly attrcted to the nucleus
• going down the group, the shared electrons get further away
  –>becoming weaker
• weakest bonds are most reactive
  –>going down the group (reactivity increases)

Question 7

why do halogenoalkanes tend to have higher b.p when there are more carbon and halogen atoms? (what is it caused by, and what’s the trend generally in other molecules):

Answer 7

• tend to have higher b.p (higher RMM and more polar)
• both of these are caused by VDW forces and larger the molecules, greater the no. of electrons
  —> in other molecules it makes them more branched which tends to decrease the m.p

Question 8

General formula of halogenoalkanes

Answer 8

CnH2n+1X