intro to organic chem

Question 1

How many electrons are shared in a double bond, e.g. C=C in ethene?

Answer 1

Four

Question 2

What is the bond angle in methane?

Answer 2

109.5o

Question 3

Define empirical formulae.

Answer 3

The simplest whole number ratio in which the atoms of each element are present in a compound.

Question 4

Define molecular formula.

Answer 4

A formula that tells us the actual number of atoms of each different element that makes up a molecule.

Question 5

Define structural formula.

Answer 5

A formula showing the atoms present in a molecule and how they are joined together.

Question 6

What does a displayed formula show?

Answer 6

A displayed formula shows all the atoms in a compound and their bonds.

Question 7

What is a hydrocarbon?

Answer 7

A compound containing only hydrogen and carbon atoms.

Question 8

Define functional group.

Answer 8

An atom, or group of atoms, in a molecule which determines its chemical properties.

Question 9

What are the three characteristics of a homologous series?

Answer 9

• Same general formula
• Same functional group
• Same chemical reactivity

Question 10

What is the general formula for an alkane?

Answer 10

CnH2n+2

Question 11

What is the general formula for an alkene?

Answer 11

CnH2n

Question 12

Define structural isomerism.

Answer 12

Two or more compounds with the same molecular formula but different structural formulae.

Question 13

State, describe and give examples of the three different types of structural isomerism.

Answer 13

1. Chain isomerism: two isomers with the same molecular formula but a different arrangement of carbon chain. For example, butan-1-ol and 2-methylpropan-1-ol.
2. Positional isomerism: two isomers with the same molecular formula but the functional group is attached to different points of the main carbon chain. For example, 1-bromopropane and 2-bromopropane.
3. Functional group isomerism: two isomers with the same molecular formula but a different functional group. For example: C5H10 can be both pentene and cyclopentane.

Question 14

Define the term stereoisomer.

Answer 14

Molecules with the same structural formula but a different arrangement of atoms in space.

Question 15

Explain why alkenes show E-Z isomerism but alkanes do not.

Answer 15

Alkenes contain a double bond that is planar and unable to rotate. Therefore, the substituent groups are locked in place and E-Z isomerism can arise. Alkanes contain only single covalent bonds that are able to rotate and, therefore, E-Z isomerism cannot occur.