Covalent Molecules 1: Intro

Question 1

What is bond strength measured in?

Answer 1

kJ/mol

Question 2

Why is the bond strength of the C=O bond not a direct double of the C-O bond?

Answer 2

More electrons present in the double bond
Increases repulsion, so although the bond strength is greater, it is not doubled

Question 3

Why is the bond length of the C=C bond not significantly shorter than the C-C bond?

Answer 3

Also due to repulsion

Question 4

What is bond length measured in?

Answer 4

Angstrom (Å)

Question 5

What is electronegativity?

Answer 5

A measure of the tendency of an atom to attract a bonding pair of electrons

Question 6

Define aliphatic.

Answer 6

An organic compound that is non-aromatic
Has a straight carbon chain

Question 7

Define aromatic.

Answer 7

A compound that contains a delocalised ring of electrons

Question 8

What is valency?

Answer 8

How many bonds an atom can form

Question 9

What are the two characteristics of carbon that give it high chemical versatility?

Answer 9

1) An atom of carbon can form covalent bonds with up to four other atosm
2) An atom of carbon can form multiple covalent bonds - i.e. double or triple bonds

Question 10

What are hydrocarbons?

Answer 10

Compounds containing only carbon and hydrogen atoms

Question 11

What are the three groups of hydrocarbon?

Answer 11

Alkane (saturated)
Alkene (containing double bonds)
Alkyne (containing triple bonds)

Question 12

What are saturated hydrocarbons?

Answer 12

Hydrocarbons containing only single bonds

Question 13

What are unsaturated hydrocarbons?

Answer 13

Hydrocarbons containing some double or triple bonds

Question 14

What are halogenoalkanes?

Answer 14

Compounds containing at least one halogen atom attached to either a single carbon or multiple carbon atoms

Question 15

What is halothane?

Answer 15

1-bromo,1-chloro,2,2,2-trifluoroethane
General anaesthetic

Question 16

What is chloroform?

Answer 16

Trichloromethane
Was once used as general anaesthetic but was found to be toxic so is no longer used

Question 17

What are chlorofluorocarbons?

Answer 17

Small molecules with central carbon atoms attached to only fluorine and chlorine
Widely used as refrigerants but found to decay in the stratosphere, converting ozone into molecular oxygen which lacks the ability to absorb UV radiation
Contributing to global warming

Question 18

What compound has replaced chlorofluorocarbons?

Answer 18

HFCs (hydrofluorocarbons)
Potent greenhouse gases
Warming effect is thought to be thousands of times stronger than carbon dioxide

Question 19

What is the steroid template?

Answer 19

Four cyclic hydrocarbon rings
Three cyclohexanes and one cyclopentane
Featured in progesterone and testosterone

Question 20

What are alkyl groups?

Answer 20

Alkane-like skeletons with one hydrogen atom removed to allow the functional group to attach
Represented with R

Question 21

Why are alkenes more chemically reactive than alkanes?

Answer 21

Because of the presence of the double bond
Valence electrons can be used to participate in new covalent bonds with other atoms

Question 22

Give two examples of alkenes found in nature.

Answer 22

Limonene - gives oranges and lemons their citrus scent
Geraniol - gives roses their characteristic smell

Question 23

What are alkynes?

Answer 23

Hydrocarbons containing at least one triple bond
Has extremely high energy so are much less stable than alkanes, but far more reactive

Question 24

What are aryl groups?

Answer 24

Any aromatic functional group
Represented with ‘Ar’
Eg. phenyl group

Question 25

What is phenol?

Answer 25

Phenyl group with an -OH attached

Question 26

Give an example of where aryl groups occur in biological molecules.

Answer 26

Phenylalanine (amino acid)
Adrenaline

Question 27

Why are hydrocarbons non-polar?

Answer 27

Neither the carbon or hydrogen atom is sufficiently electronegative to cause significant polarity within the molecule
Therefore very few non-covalent interactions can occur

Question 28

What is the only non-covalent interaction that hydrocarbons experience?

Answer 28

Dispersion forces
The transitory attraction between areas of opposite charge which is a consequence of the continual movement of electrons in a molecule

Question 29

Why do hydrocarbons have low melting and boiling points?

Answer 29

Requires very little energy to overcome weak dispersion forces

Question 30

How do melting points change as size of hydrocarbon increases?

Answer 30

As hydrocarbon size increases, melting point also increases as there are greater dispersion forces due to increased number of electrons

Question 31

Are hydrocarbons soluble in water, and why?

Answer 31

Hydrocarbons are insoluble in water
Because they are non-polar
And unable to form hydrogen bonds

Question 32

Why do hydrocarbons have few direct roles in biological systems?

Answer 32

They are non-polar
And therefore cannot interact with water molecules
Biological systems are aqueous

Question 33

What gives alkanes their stability?

Answer 33

Strong covalent bonds
Requires lots of energy to break
Also causes lack of reactivity

Question 34

What is the symbol for electronegativity and how is it measured?

Answer 34

Chi (ꭓ)
Measured up to the number 4.0

Question 35

What happens when there is a significant difference in electronegativity between two covalently bonded atoms?

Answer 35

The more strongly electronegative atom will be able to attract the bonding pair of electrons and become ẟ-negative
This starves the other atom of electron density, giving it a ẟ-positive charge
This is a polar bond