Module 4: Section 1 - Basic Concepts and Hydrocarbons

Question 1

What is organic chemistry?

Answer 1

Organic chemistry is the study of substances that contain carbon atoms.

Question 2

Why is this branch of chemistry known as Organic Chemistry?

Answer 2

All living things are made up from carbon compounds, and so this branch of chemistry was historically known as organic chemistry (organic = made from plants and animals).

The main source of organic compounds are living, or once or once living materials from plants and animals. However it has been discovered that these carbon compounds could also be made in the lab from non-living materials-chemicals.

Question 3

What does modern organic chemistry study?

Answer 3

Modern organic chemistry studies the structure, properties, composition, reactions and preparation of carbon-containing compounds.

Question 4

Why is the study and practice of organic chemistry important?

Answer 4

Carbon compounds are vital in every area of modern life: pharmaceuticals, detergents, dyes and pigments, cosmetics, plastics, and agricultural chemicals are all organic compounds - they all contain the element carbon.

Question 5

Other than carbon, what elements are present in organic compounds?

Answer 5

In addition to carbon, organic compounds commonly contain H, together with smaller amounts of O (oxygen), N (nitrogen) or S (sulphur), amongst other elements.

The number of different combinations of these atoms means there is a huge variety of organic molecules possible, ranging from drugs such as aspirin to material such as plastics.

Question 6

Name one source of organic compounds.

Answer 6

Today, the vast majority of organic compounds used are produced from fractions of crude oil.

Question 7

Where is crude oil found?

Answer 7

Crude oil is a finite resource found under the ground in rocks.

Question 8

What is crude oil made from?

Answer 8

Crude oil is the remains of dead plants and animals mainly consisting mainly of plankton that was buried in mud.

Question 9

What is the structure of crude oil?

Answer 9

Crude oil is a mixture of hydrocarbons.

Question 10

Define hydrocarbon.

Answer 10

A hydrocarbon is a compound containing hydrogen and carbon only.

So C10 H22 (decade, an alkane) is a hydrocarbon, but CH3 COOC3 H7 (an ester) is not- it contains oxygen.

Question 11

What is the structure of carbon?

why’s it so special?

Answer 11

• Carbon is in group four of the periodic table, with four electrons in its outer shell.
• Each carbon atom can form four covalent bonds to other atoms. These can be single, double and even triple bonds.
• Carbon atoms can bond to other carbon atoms to form long chains.

Question 12

What are the two forms of hydrocarbons?

Answer 12

Hydrocarbons can be saturated or unsaturated.

Question 13

What is a saturated hydrocarbon?

Answer 13

A saturated hydrocarbon has single bonds only.

Question 14

What is an unsaturated hydrocarbon?

Answer 14

An unsaturated hydrocarbon contains one or more carbon-to-carbon double (or triple) bonds.

Question 15

What does nomenclature mean?

Answer 15

All nomenclature means is naming the molecules using specific rules.

Question 16

What is nomenclature?

Answer 16

The system used for naming organic compounds.

Question 17

Why is nomenclature so important?

Answer 17

As there are so many organic compounds a universal system of naming organic molecules is needed to keep track of them all.

IUPAC is an organisation that was founded in 1919 by chemists from industry and education who recognised the need for standardisation of the names of compounds.

This means that chemists across the globe can communicate clearly.

Question 18

What is a functional group?

Answer 18

A functional group is the part of the organic molecule that is largely responsible for the molecule’s chemical properties.

Question 19

Do all organic molecules contain the same functional group?

Answer 19

No.
In addition to hydrogen, carbon can bond to other elements, including oxygen, nitrogen, and halogens. This results in the formation of molecules containing different functional groups, such as alcohol and amine groups.

Question 20

How are organic compounds organised?

Answer 20

Carbon compounds are so numerous that it is convenient to organise them into families of compounds with similar chemical structures and properties.

Question 21

Define homologous series.

Answer 21

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

Question 22

Explain what a homologous series is?

Answer 22

• An homologous series is a family of organic compounds that have the same functional group, but different carbon chain length.
• Each member of the series differs from the next by one CH2 unit.
• The members have similar chemical properties, and the physical properties such as melting and boiling points increase gradually as the size (and hence the intermolecular forces) increases.

Question 23

What are the majority of hydrocarbons in crude oil called?

Answer 23

Most of the hydrocarbons in crude oil are called alkanes.

Question 24

What is the simplest homologous series?

Answer 24

The simplest homologous series is the alkanes.

Alkanes contain single carbon-to-carbon bonds.

Question 25

What are the first three members of the homologous series of the alkanes?

Answer 25

1. Methane (CH4)+ CH2
2. Ethane (C2H6)

   \+ CH2

3. Propane (C3H8)

Question 26

What affects the properties of hydrocarbons? And what 3 things does this effect?

Answer 26

The more carbon atoms a hydrocarbon molecule has, the longer, larger and heavier it will be. This will affect its physical properties:

• Boiling Point. Longer molecules have a higher boiling point because they are heavier, move more slowly, become tangled, have greater intermolecular forces and therefore require more heat energy to gain enough speed/energy to leave the surface of the liquid to become a gas, i.e. boil/evaporate.
• Flammability. Smaller (weaker) molecules burn more easily e.g. methane, butane or octane. Larger molecules do not tend tend to burn, e.g bitumen-you can’t easily set fire to the road! Therefore, the smaller hydrocarbons tend to be used as fuels.

*Viscosity (thickness): Longer molecules become more tangled, possess greater intermolecular forces and are less able to move past each other-compare octane (8 carbons clumped together like pasta) and bitumen (120 carbons tangled like spaghetti).
The shorter the molecules, the more runny the hydro carbon is- that is, the less viscous it is.

Question 27

Give three reasons why carbons form a large number of compounds…

Answer 27

d

Question 28

Why are formulas used to represent molecules?

Answer 28

Picturing molecules can be difficult if you can’t see them around you.

We can use elemental symbols from the periodic table to help visualise molecules. For example, a molecule of methane is one carbon atom attached to four hydrogen atoms. You could show this by giving its molecular formula, Ch4 or you could draw its displayed formula.

Whilst drawing a displayed formula isn’t exactly what methane looks like, but visualising it like this lets us compare it to other molecules.

This means we can predict its properties and how it might react with other molecules.

Molecular models can also be use to represent molecules.

Question 29

How can organic molecules be represented?

Answer 29

Organic compounds can be represented by:

1. General formula
2. Empirical formula
3. Molecular formula
4. Structural formula
5. Skeletal formula
6. Displayed formula

Question 30

What does the term general formula mean?

Answer 30

A GENERAL FORMULA is an algebraic formula that can describe ANY MEMBER of a family of compounds.

For example, alcohols have the general formula:
Cn H2n+1 OH.

Question 31

Is organic chemistry the study of individual compounds?

Answer 31

Organic chemistry is more about groups of similar chemicals than individual compounds.

(These groups are called homologous series.
A homologous series is a family of compounds that have the same functional group and general formula. N.b. consecutive members of a homologous series differ by CH2.

Question 32

What is the general formula for alkanes?

Why is the general formula important?

Answer 32

(The simplest homologous series is the alkanes.

Alkanes contain single carbon-to-carbon bonds.

They’re straight chain molecules that contain only carbon and hydrogen atoms.

There are always twice as many hydrogen atoms as carbon atoms, plus two more. So the general formula is Cn H2n+2.)

You can use this formula to work out how many hydrogen atoms there are in any alkane if you know the number of carbon atoms.

Question 33

What does the term molecular formula mean?

Answer 33

A molecular formula gives the ACTUAL number of atoms of each element in a molecule.

E.g. C4H10 O

Tip: Molecular formulas tell you what atoms are in a molecule, but they don’t tell you which atoms are bonded to which.

Question 34

What does the term empirical formula mean?

Answer 34

An empirical formula gives the simplest whole number ratio of atoms of each element in a compound.

Question 35

How do you calculate the empirical formula of a molecule?

Answer 35

To find the empirical formula you have to divide the molecular formula by the smallest number of atoms for a given element in the molecule.

E.g. If the molecular formula is C2H4CL2, the smallest number of atoms is 2 (for both C and Cl). So you divide the molecular formula by 2 and get the empirical formula CH2CL.

The number of each type of atom in the empirical formula needs to be a whole number. So if you divide the molecular formula by the smallest number of atoms and end up without whole numbers, the molecular formula will be the same as the empirical formula.

Question 36

What does the term structural formula mean?

Answer 36

It shows the arrangement of atoms in a molecule without showing every bond.

E.g. CH3CH2CH2CHCH2.

Question 37

What does the term displayed formula mean?

Answer 37

It shows every atom and every bond in a molecule.

Question 38

Define skeletal formula.

Answer 38

A type of formula which is drawn as lines with each vertex being a carbon atom. Carbon atoms not drawn, assumed each C atom has all unspecified bonds as C-H

Question 39

What does the term skeletal formula mean?

Answer 39

Shows the bonds of the carbon skeleton only, with any functional groups.

The hydrogen + carbon atoms aren’t shown.

Question 40

Why is skeletal formula useful?

Answer 40

It’s handy for drawing large complicated structures, like cyclic hydrocarbons as its faster and so more convenient.