CHAPTER 12 - ALKANES Flashcards
What is the general formula for alkanes
CnH2n+2
Are alkanes saturated or unsaturated hydrocarbons
Saturated
What bond is present in alkanes
Single covalent bonds, Sigma bonds
What is a covalent bond
A shared pair of electrons
What is a Sigma bond
The overlapping of two orbitals, one from each bonding atom
How many sigma bonds does each carbon have
4
What is the shape arrangement around each atom and their bonding angle
Tetrahedral, 109.5
How is crude oil separated
Fractional distillation (in a distillation tower)
Why does the boiling point increase as carbon chain length increases?
Increase in Intermolecular forces (LDFs)
As chain length increases, molecules have larger surface area, and greater contact is possible, hence more energy is required to overcome forces
What effect does branching have on boiling point and why
Boiling point decreases as branching increases
Fewer points of contact between molecules of branched molecules, giving fewer London forces
Kerosene is obtained from crude oil. Name the process used to obtain kerosene from crude oil and explain how the process works
Factional distillation
Different fractions have different boiling points
Increase the temperature of the system so each fraction vaporises separately and other fractions can be collected
Explain why the straight-chain isomer of C10H22 has higher boiling point than any of its branched-chain isomers
There is more surface contact between straight-chain isomer so it has more/stronger London forces
More energy required to break these London forces
Explain why the boiling points increase down the alkane homologous series
As the chain length increases, there are more points of contact between molecules, meaning more London forces
More energy is required to break these bonds
Describe the bonding in ethane. State and explain the H-C-H bond angle in a molecule of ethane
Single bonds between the C-C and the C-H are sigma bonds
Sigma bonds is the overlap of orbitals, one from each bonding atom
Each carbon atom is bonded to four other atoms by covalent bonds.
The shape around each carbon atom is tetrahedral.
The four bonding pairs of electrons repel equally to give a bond angle of 109.5 around the carbon atom
Why are alkanes relatively unreactive
C-C and C-H bonds are strong
C-C bonds are non-polar
C-H bonds are non-polar as their electronegativity is very similar
