Chemistry Module 4.1 - page 89

Question 1

What is the general formula?

Answer 1

The general formula is an algebraic formula that can describe any memeber of a family of compounds.

E.g. C_nH_2n+1OH (for all alcohols).

Question 2

What is the empirical formula?

Answer 2

The simplest whole number ratio of atoms of each element in a compound.

E.g. Ethane, C₂H₆, would have an empirical formula of CH₃.

Question 3

What is the molecular formula?

Answer 3

The molecula formula is the actual number of atoms of each element in a molecule.

Question 4

What is the structural formula?

Answer 4

Shows the arrangement of atoms carbon by carbon, with the attached hydrogens and functional groups.

E.g. Propane would have the structural formula of CH₃CH₂CH₃.

Question 5

What is the skeletal formula?

Answer 5

The skeletal formula shows the bonds of the carbon skeleton only, with any functional groups. The hydrogen and carbon atoms aren’t shown. This is handy for drawing large complicated strcutures, like cyclic hydrocarbons.

Question 6

What is the displayed formula?

Answer 6

The displayed formula shows how all the atoms are arranged, and all the bonds between them.

Question 7

What is a homologous series?

Answer 7

A homologous series is a bunch of organic compounds that have the same functional group and general formula.

Question 8

What is the suffix of an alkane? Give an example.

Answer 8

Suffix: -ane

E.g. Propane, CH₃CH₂CH₃

Question 9

What is the suffix for a branched alkane? Give an example.

Answer 9

Suffix: alkyl- (-yl)

E.g. Methylpropane, CH₃CH(CH₃)CH₃

Question 10

What is the suffix for alkenes? Give an example.

Answer 10

Suffiix: -ene

E.g. Propene, CH₃CH=CH₂

Question 11

What is the prefix for haloalkanes? Give an example.

Answer 11

Prefix: chloro-/bromo-/iodo-

E.g. Chlorothane, CH₃CH₂Cl

Question 12

What is the suffix for alcohols? Give an example.

Answer 12

Suffix: -ol

E.g. Ethanol, CH₃CH₂OH

Question 13

What is the suffix for aldehydes? Give an example.

Answer 13

Suffix: -al

E.g. Ethanal, CH₃CHO

Question 14

What is the suffix for ketones?

Answer 14

Suffix: -one

E.g. Propanon, CH₃COCH₃

Question 15

What is the prefix and suffix of cycloalkanes?

Answer 15

Suffix and Prefix: cyclo-…-ane

E.g Cyclohexane, C₆H₁₂

Question 16

What is the suffix for carboxylic acids?

Answer 16

Suffix: -oic acid

E.g. Ethanoic acid, CH₃COOH

Question 17

What is the prefix and suffix of esters?

Answer 17

Prefix and suffix: alkyl-…-anoate

E.g. Methyl propanoate, CH₃CH₂COOCH₃

Question 18

What do all organic compounds contain?

Answer 18

All organic compounds contain a carbon skeleton. This can be either aromatic or aliphatic.

Question 19

What is an aromatic compound?

Answer 19

An aromatic compound is an organic compound which contains a benzene ring.

Question 20

What is an aliphatic compound?

Answer 20

An aliphatic compound contain carbon and hydrogen joinmed together in straight chains, branched chains or non-aromatic rings.

Question 21

What name would you give to an aliphatic compound which contains a (non-aromatic) ring?

Answer 21

If an aliphatic compound contains a (non-aromatic) ring, then it can be called alicyclic.

Question 22

What is a saturated compound?

Answer 22

A saturated compound only contain carbon-carbon single bonds - like alkanes.

Question 23

What is an unsaturated compound?

Answer 23

An unsaturated compound can have carbon-carbon double bonds, triple bonds or aromatic groups.

Question 24

What is an alkyl group?

Answer 24

An alkyl group is a fragment of a molecule with general formula C_nH_2n+1.

Question 25

GIve the method to name organic compounds.

Answer 25

1. Count the carbon atoms in the longest continuous chain -thid gives you the stem.
2. The main functional groupof the molecule usually tells you what homologous series the molecule is in, and so gives you the prefix or suffix.
3. Number the longest carbon chain so that the main functional group has the lowest possible number. If there’s more than one longest chain, pick the one with the most side chains.
4. Any side chains or less important functional groups are added as prefixes ath the start of the name. Put them in alphabetical order, after the number of the carbon atom each is attached to.
5. If there’s more than one identical side chain or functional group, use di- (2), tri- (3), tetra- (4) before that part of the name - but ignore this when working out the alphabetical order.

Question 26

When are two molecules considered to be isomers of one another?

Answer 26

Two molecules are isomers of one another if they have the same molecular formula but the atoms are arranged differently.

Question 27

What is a structural isomer?

Answer 27

A strucutural isomer is a molecule which has the same molecular formula but a different structural formula.

Question 28

What are the three types of strucutural isomers.

Answer 28

The three types of structural isomers are:

Chain isomers, positional isomers and functional group isomers.

Question 29

What is a chain isomer?

Answer 29

In a chain isomer, the carbon skeleton can be arranged differently, e.g. as a straight chain, or branched in different ways.

These isomers have similar chemical properties - bu their physical properties, like boiling point, will be different because of the change in shaoe of the molecule.

Question 30

What is a positional isomer?

Answer 30

In a positional isomer, the skeleton and fucntional group could be the same, only the functional group attached to a different carbon atom.

These also have different physical properties, and the chemical properties might be different too.

Question 31

What is a functional group isomer?

Answer 31

In a functional group isomer, the same atoms can bed arranged into different functional groups.

These have very different physical and chemical properties.

Question 32

What can atoms do around single C-C bonds?

Answer 32

Atoms can rotate as much as they want around single

C-C bonds. Therefore, a molecule may look like it has an isomer when it really doesn’t.

Question 33

What is an alkane?

Answer 33

Alkanes are saturated hydrocarbons.

Question 34

What is the general formula for an alkane?

Answer 34

Alkanes have the general formula C_nH_2n+2.

Question 35

How many bonds does a carbon atom have with other atoms in an alkane?

Answer 35

Every carbon atom in an alkane has four single bonds with other atoms.

Question 36

Are alkanes saturated or unsaturated hydrocarbons?

Answer 36

Alkanes are saturated - all the carbon-carbon bonds are single bonds.

Question 37

Give the general formula of a cycloalkane.

Answer 37

C_n+2n is the general formula of cycloalkanes.

Question 38

Explain why alkane molecules are tetrahedral around each carbon.

Answer 38

In an alkane molecule, each carbon atom has four pairs of bonding electrons around it. They all repel each other equally. So the molecule forms a tetrahedral shape around each carbon. Each bond angle is 109.5º.

Question 39

Explain why the boiling point of an alkane depends on its size and shape.

Answer 39

1. Alkanes have covalent bonds inside the molecules. Between the molecules, there are induced dipole-dipole interactions which hold them together.
2. The longer the carbon chain, the stronger the induced dipole-dipole interactions. This is because there’s more surface contact and more electrons to interact.
3. As the molecules get longer, it takes more energy to overcome the induced dipole-dipole interactions, and the boiling point rises.
4. A branched chain alkane has a lower boiling point than its straight chain isomer. Branched chain alkanes can’t pack closely together and they have smaller molecular surface areas - so the induced dipole-dipole interactions are reduced.

Question 40

Detail the reaction between alkanes and oxygen (combustion).

Answer 40

1. If you burn (oxidise) alkanes with oxygen, you get carbon dioxide and water - it’s a combustion reaction.
2. Combustion reactions happen between gases, so liquid alkanes have to be vaporised first. Smaller alkanes turn into gases more easily (they’re more volatile), so they’ll burn more easily too.
3. Larger alkanes release more energy per mole because they have more bonds to react.
4. Because they release so much energy when they burn, alkanes make excellent fuels.