Properties Of Alkanes Flashcards
(20 cards)
What type of bonds do alkanes have?
Single covalent bonds also known as sigma bonds.
What do sigma bonds allow for?
Free rotation of the groups around the bond
What is a sigma bonds and what do they allow for?
A sigma bond is when 2 orbitals overlap and share electrons. They allow for free rotation of the groups around the bond
What is SP hybridisation and why does it occur
This is when carbon promotes a 2s electron to a higher energy state. This can occur because the energy gap between 2s and 2p is small.
How many identical orbitals are formed from sp hybridisation
4
What shape are sp orbitals
They look like half a p orbital
Define and alkane
Saturated hydrocarbon
Describe sp hybridisation in a hydrocarbon
When 2s orbital from a carbon atom is excited the 2s and 2p orbitals are rearranged to form hybrid orbitals
Why are they called sp3 orbitals
There are 3 p orbitals and 1 s orbital
What are intermolecular forces in alkanes affected by?
Chain length and branching
What type of molecules are alkanes and what does this mean for their type of intermolecular forces
Alkanes are non polar molecules so they only have induced dipole-dipole interactions (London/ dispersion forces)
What does more points of contact result in?
More points of contact result in more intermolecular forces so more energy is requires to break them
Why is boiling point higher in long chain alkanes.
There are more points of contact therefore more energy is required to break the. So the boiling point is higher.
What is packing
This describes how closely molecules can get together
Why do molecules that are branched have a lower boiling point?
Branched molecules are unable to pack together as tightly as straight chains so they have:
Less points of contact
Fewer London forces
What is viscosity?
How runny a substance is.
What is the viscosity of long chain hydrocarbons and why?
Very viscous because there are more points of surface contact and a higher number of intermolecular forces to break
Why are branched molecules less viscous than straight chained molecules?
Opposite reasoning to straight chained molecules:
Less points of surface contact
Fewer intermolecular forces
What is volatility?
Volatility is how easily a substance turns into a gas, so the lower the boiling point the more volatile a substance is.
Why are branched chains more volatile than straight chains?
They have lower boiling points.
