halogens Flashcards
what are halogen alkanes
halogen alkanes have an alkane skeleton with one or more halogen (fluorine, chlorine, bromine or iodine) atoms in place of hydrogen atoms
what is the general formula of halogen alkanes
Cn H2n+1x - formula for a halogenalkane with a single halogen atom and where x is a halogen
This formula is sometimes shortened to R-x
what is the bond polarity
halogen alkanes have a C -x bond
This bond is polar
C-X because halogens are more electronegative than carbon
what is the solubility of halogenalkanes
the polar C-x bonds are not polar enough to make the halogenalkanes soluble in water
what is the main intermolecular forces in halogenalkanes
the main intermolecular forces of attraction are dipole - dipole attractions and van der Waal forces
halogenalkanes mix with hydrocarbons so they can be used as dry - cleaning fluids and to remove only stains (oil is a mixture of hydrocarbons)
what is the boiling points of haloalkanes
the boiling point depends on the number of carbon atoms and halogens atoms
the boiling point increases with increased chain length
boiling point increases going down the halogen group
this is because the increased van der Waals forces because the larger the molecules, the greater the number of electrons (and therefore the larger the van der Waals forces)
why do haloalkanes have higher boiling points than alkanes with similar chain lengths
halogenalkanes have higher boiling points than alkanes with similar chain lengths because they have higher relative molecular masses and they are polar
how do halogenalkanes react
when halogenalkanes react it is almost always the C-X bond that breaks
There are two factors that determine how readily the C-X bond reacts
These are:
- the C-X bond polarity
- the C-X bond enthalpy
what is the bond polarity of halogenalkanes
the halogens are more electronegative than carbon so the bond polarity will be C+-X-
C :X
This means that carbon bonded to the halogen has a partial positive charge - it is electron deficient
This means that it can be attached by reagents that are electron rich or have electron - rich areas.
These are called nuclophiles
what is a nucleophile
a nucleophile is an electron pair donor
which C-X bond is the most polar
the polarity of the C-X bond would predict that the C-F bond would be the most reactivr
It is the most polar, so the C+ has the most positive charge and is therefore most easily attacked by a nucleophile
This argument would make the C - I bond least reactive because it is the least polar
what happens to the bond enthalpies going down the group
C-X bond enthalpies get weaker going down the group
Fluorine is the smallest atomof the halogens and the shared electrons in the C-F bond are strongly attracted to the fluorine nucleus
This makes a strong bond
why does the C-X bond get weaker gong down the group
going down the group, the shared electrons in the C-X bond get further and further away from the halogen nucleus, so the bonds becomes weaker
the bond enthalpies would predict the iodo- compounds with the weaker bonds are the most reactive, and fluro - compounds with thee strongest bonds, are the least reactive
what does reactivity of the haloalkanes depend on
as reactivity increases as you go down the group, it shows that bond enthalpy is more important factor than bond polarity
what are nucleophiles
- are reagents that attack and form bonds with positively or partially positively charged carbon atoms
- a nucleophhilic is either a negatively charged ion or has an atom with a - delta charge