4.1.2 Alkanes Flashcards
what are alkanes?
saturated hydrocarbons containing single C-H and C-C bonds
what bonds so alkanes have? π or σ
σ
what rotation does the σ bond have?
free rotation
what shape do alkanes have?
tetrahedral
what bond angle do alkanes have?
109.5
what homologue series do alkanes belong to?
series with general formula CnH2n+2
which alkanes differ from the general formula?
cycloalkanes (though they are still saturated hydrocarbons)
how many σ bonds does each C atom form in an alkane?
4
why do alkanes have a tetrahedral shape?
the shape minimises the electron- electron repulsion between the bonding pairs
do longer chained alkanes have lower or higher boiling points?
higher
why do longer chained alkanes have higher boiling points?
as the chain length increases, so does the Mr, this results in stronger London forces between the chains
do branched chain alkanes have lower or higher boiling points than straight chain alkanes?
lower
why do branched chain alkanes have lower boiling points than straight chain alkanes?
branching of alkane chains weakens the London forces between the chains, as they are less able to pack together tightly. tf the distance over which the London forces act is increased and attractive forces are weakened
do alkanes have low or high reactivity with many reagents?
low
why do alkanes have low reactivity with many reagents?
due to the high C-C bond enthalpy and the very low polarity of the σ-bonds present?
