Module 4: Chapter 11&12 Organic Chemistry & Alkanes

Question 1

Define general formula

Answer 1

The simplest algebraic formula of a member of a homologous series e.g. CnH2n+2

Question 2

Define structural formula

Answer 2

The minimal detail that shows the arrangement of atoms in a molecules e.g. CH3CH2CH2CH3

Question 3

Define displayed formula

Answer 3

Shows the relative positioning of atoms and the bonds between them

Question 4

Define skeletal formula

Answer 4

Simplified organic formula, shown by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups

Question 5

Define homologous series

Answer 5

A series of organic compounds having the same functional group but with each successive member differing by CH2

Question 6

Define functional group

Answer 6

A group of atoms responsible for the characteristic reactions of a compound
- alkanes is the only family that doesn’t have a functional group

Question 7

Define aliphatic

Answer 7

A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings

Question 8

Define alicyclic

Answer 8

An aliphatic compound arranged in non-aromatic rings with or without side chains

Question 9

Define aromatic

Answer 9

A compound containing a benzene ring

Question 10

Define saturated

Answer 10

A molecule with single carbon to carbon bonds only

Question 11

Define unsaturated

Answer 11

A molecule with multiple carbon-carbon bonds including double and triple carbon-carbon bonds and aromatic rings

Question 12

Define structural isomers

Answer 12

compounds with the same molecular formula but with a different structural formulae

Question 13

Define homolytic fissions

Answer 13

When a bond breaks and each bonding atom receives one electron from the bonded pair to form 2 radicals

Question 14

Define heterolytic fission

Answer 14

When a bond breaks and one bonding atom receives both electrons from the bonded pair to form ions

Question 15

Define radical

Answer 15

A species with an unpaired electron

Question 16

What are the rules for naming alkanes?

Answer 16

1. find the longest continuous carbon chain
2. identify any substituent group
3. number carbon atoms in longest chain to indicated position of any substituent groups (start numbering from the end that produces lowest set of numbers)
4. if same alkyl group appears more once indicated in name with di-, tri- and tetra- and use commas to separate numbers
5. names of different substituents are arranged alphabetically regardless of numbers

Question 17

Why is carbon special?

Answer 17

• all carbon compounds are covalent
• each carbon atom forms 4 covalent bonds
• carbon forms strong covalent bonds with itself to form rings and chains

Question 18

What are hydrocarbons?

Answer 18

only contain carbon and hydrogen and have the general formula CxHy

Question 19

What is the molecular formula?

Answer 19

Gives the number of different types of atom in the molecule

Question 20

What is the empirical formula?

Answer 20

Gives the ratio of the different types of atom in the molecule

Question 21

What are the 3 types of structural isomers?

Answer 21

Chain, position and functional group

Question 22

Describe position isomerism

Answer 22

in compounds containing a functional group, the functional group can be at different positions along the carbon chain

Question 23

Describe functional group isomerism

Answer 23

molecules containing different functional groups have the same molecular formula

Question 24

What are alkanes?

Answer 24

• hydrocarbons; they contain carbon and hydrogen only
• they are saturated, only single carbon-carbon bonds
• general formula of CnH2n+2

Question 25

What are the first 10 alkanes?

Answer 25

methane (CH4)
ethane (C2H6)
propane (C3H8)
butane (C4H10)
pentane (C5H12)
hexane (C6H14)
heptane (C7H16)
octane (C8H18)
nonane (C9H20)
decane (C10H22)

Question 26

What are the bonds and shape of alkanes?

Answer 26

• Alkanes contain single C-C bonds
• 2 s orbitals overlap to form a bond between the 2 carbon atoms that share a pair electrons, this is a sigma (σ) bonds
• alkanes have a tetrahedral structure with a bond angle of 109.5°

Question 27

What are the boiling points of alkanes?

Answer 27

The boiling point is determined by the intermolecular force present and the size of the molecule (chain length)

• in crude oil there are lots of variations of boiling points so oil refineries separate crude oil into fractions by fractional distillation
• the greater the chain length, the greater the London forces, the higher the boiling point
• longer chains have a larger surface area, more contact between molecules, London forces are greater, more energy required to overcome forces
• same applies to the shape of the chain, the more branching, the less surface area of contact and the weaker the London forces

Question 28

What is the alkane reactivity?

Answer 28

• strong sigma bonds throughout
• non polar bonds throughout
• generally not very reactive

Question 29

Describe combustion of alkanes?

Answer 29

• alkanes combust very well

- in plentiful supply of oxygen complete combustion results in the production of H2O and CO2

Question 30

Describe the incomplete combustion of alkanes?

Answer 30

Most fuels don’t burn completely in oxygen. Either CO and H2O or C and H2O are formed
- CO is odourless, colourless, tasteless and highly toxic
(- CH4 is a greenhouse gas 22 more times potent than CO2)

Question 31

What is radical substitution?

Answer 31

Involves homolytic breaking of covalent bonds

A radical is produced

Question 32

Describe chlorination of methane

Answer 32

CH4 + Cl2 -> CH3Cl + HCl (under conditions of UV light and in excess of methane
Initiation step (homolytic fission): Cl2 -(UV)-> Cl· + Cl·

Propagation steps:
CH4 + Cl· -> HCl + CH3·
CH3· + Cl2 -> CH3Cl + Cl·

Termination step:
CH3· + Cl· -> CH3Cl

Minor termination step:
CH3· + CH3· -> CH3CH3