Properties of alkanes Flashcards
what type of bond are in carbon atoms of alkanes?
a covalent bond called sigma bond
how is a sigma bond formed?
overlap of two orbitals , one from each bonding atom , each containing one electron
what is the bond angle in each carbon atom in an alkane?
109.5 degrees
why does boiling point increase as alkane chain length becomes longer?
increased chain length therefore greater surface area of contact. As a result, there are stronger london forces
what is the reactivity of alkanes
alkanes do not react with common reagents as they are not very reactive
why does boiling point decrease as branching in alkane increases?
there are less surface areas of contact therefore weaker london forces. Also , branches alkanes prevent close packing of carbon atoms therefore decreasing the intermolecular forces.
why are alkanes not very reactive?
C-C and C-H sigma bonds are strong
C-C bonds are non-polar
C-H have very similar electronegativity so are considered as non polar
what is the reaction of alkanes with halogens?
alkanes react with halogens in the presence of UV radiation which provides the energy
CH4 + Br2 —– CH3Br + HBr
what is the name of the mechanism for the bromination of methane
radical substitution
what is step 1: Initiation
halogen ( bromine , Br2) splits by homolytic fission forming 2 bromine radicals.
what causes the splitting of bromine in step 1
uv radiation
what is step 2 : Propagation
Bromine radical reacts with C-H in CH4 ( methane) to form CH3radical and HBr
CH3 radical reacts with Br2 ——– CH3Br + Br radical
what is step 3: termination:
br radical + br radical —– Br2
CH3 radical + CH3 radical ——- C2H6
CH3 radical + Br radical —– CH3Br
