11.1 Carbon compounds

Question 1

What is special about the element carbon

Answer 1

Carbon can form rings and long chains which may be branched because…

. An atom of it has 4 electrons on its outer shell, so it forms 4 covalent bonds
. Carbon-carbon bonds are relatively strong, (347KJmol) and NON polar

Question 2

Why are carbon-hydrogen bonds stronger than carbon-carbon

Answer 2

• Because hydrogen has only one electron shell so is smaller than carbon
• This means that the distance between nuclei and outer shell is much shorter than carbons so there is a greater force of attraction between nucleus and the shared pair of electrons

Question 3

What are 3 ways carbon can form bonds

Answer 3

. It can form single bonds, eg in methane where one carbon bonds to 4 hydrogens

. It can form one double bond and two single bonds eg in ethene

. It can form one single bond and one triple bond eg in ethyne
H - C =- C- H
Those are meant to be 3 bonds

Question 4

What is empirical formula

Answer 4

. Formula showing the simplest ratio of atoms of each element present in a compound

Eg question: 3g of Ethane contains 2.4g of carbon (Mr 12) and 0.6g of hydrogen (mr 1)
What is its empirical formula?

Find moles of both:
Carbon: 0.2 moles
Hydrogen: 0.6 moles

Divide both by smaller number (0.2) to give ratio 1:3 of C:H
so it is CH3

Question 5

what is molecular formula

How is it found

Answer 5

The formula that shows the actual number of atoms in each element in the molecule

It is found from:
- Empirical formula
- Relative atomic mass of empirical formula
- Relative molecular mass of the molecule

Example: Empirical formula of something is CH3, and this group of atoms have Ar: 15.0
The Ar of ethane is 30.0

So do 30/15 which is 2 so times all the atoms of CH3 by 2
This makes C2H6 which is ethane

Question 6

What is displayed formula

Answer 6

It shows every atom and every bond in the molecule:
Eg using -, or = to represent single and double bonds

Question 7

What is structural formula

Answer 7

It shows the unique arrangement of atoms in a molecule, without showing all the bonds
Eg CH3CH3 would be written to represent ethane

Each carbon is written separately, with the atoms or groups that are attached to it

Or CH3CH2CH2OH
Which is propanol

Any branches on the carbon chain are written in brackets

Question 8

What is skeletal formula

Answer 8

With more complex molecules, it is quicker to not draw carbon , so straight lines represent carbon-carbon bonds.
Hydrogen is also not drawn

And carbon atoms are each edge of it, so where the two lines/bonds meet.

Skeletal formula give us a rough idea of bond angles
Eg they are 109.5 in an unbranched alkane chain

Question 9

What is 3 dimensional structural formula

Answer 9

Show 3D structure using dotted lines and wedges

Bonds coming out of the paper are represented by wedges
And bonds going into the paper are represented by dotted lines —

Question 10

What are reaction mechanisms

Answer 10

Curly arrows can be used to show wear electrons move to.

As electrons are negatively charged, they tend to move to areas from high electron density to more positively charged areas.

Eg a lone pair of electrons will be attracted to positive end of a polar bond eg C f+

So curly arrow goes from lone pair, either on a covalent bond or on a molecule with a lone pair, and it points towards a positively charged area on the molecule

Question 11

What are free radicals

Answer 11

Sometimes a covalent bond (pair of electrons between two atoms) will break so one electron goes to each atom that forms the bond

So eg Cl2 makes .Cl + .Cl
where the . is the electron

Free radicals are very reacive

Question 12

Describe structure of functional group nitrile

Answer 12

There is a triple carbon-nitrogen bond

eg propanenitrile
Is C2H5CN
So the suffix is nitrile, and there is no prefix

Question 13

Describe structure of amine functional group

Answer 13

. Prefix is amino
. Suffix is amine

Where there is an N bonded to two hydrogens

Ethanamine or ethylamine
Is C2H5NH2

Question 14

What is the structure of functional group acyl chloride

Answer 14

The suffix is oyl chloride

The functional group is Carbon with a double bond to oxygen above it, and a single bond to oxygen beside it

So eg CH3C(=O)Cl Which is
ethanoyl chloride

Question 15

Describe functional group acid anhydride

Answer 15

Suffix is oic anhydride

It is where there is an oxygen joining two C=O
so O=C– O –C=O

Eg ethanoic anhydride

CH3C(=O)O-C(=O)CH3

Question 16

Describe functional group of an ester

Answer 16

. O-C=O so the carbon is double bonded to one O and single bonded to the other O

Similar to acid anhydride

suffix is oate
Eg methyl propanoate
C(CH3)OC(=O)H2CH3

Question 17

Describe functional group of an amide

Answer 17

Suffix is amide

It is C(=O)- NH2
So similar to an amine as it has NH2 but there is also a double carbon oxygen bond

Ethanamide
CH3C(=O)NH2