Bonding - Covalent

Question 1

Define covalent bonding

Answer 1

The electrostatic attraction between the nuclei of two atoms and one or more shared pairs of electrons between them

Question 2

Double bond

Answer 2

Where two pairs of electrons are shared

Question 3

Triple bond

Answer 3

Where three pairs of electrons are shared

Question 4

Features of a valence structure

Answer 4

Bonding pairs shown as lines, non-bonding electrons shown as dots

Question 5

Features of a Lewis structure

Answer 5

All valence electrons shown as dots (bonding and non-bonding)

Question 6

Features of a structural formula

Answer 6

Bonding pairs shown as lines, no lone pairs shown

Question 7

Shape of methane (CH4)

Answer 7

Tetrahedral (4 bonding groups, no lone pairs)

Question 8

Shape of ammonia (NH3)

Answer 8

Trigonal pyramidal (3 bonding groups, one lone pair)

Question 9

Shape of water (H2O)

Answer 9

Bent (2 bonding groups, 2 lone pairs)

Question 10

Shape of boron trichloride (BCl3)

Answer 10

Trigonal planar (3 bonding groups, no lone pairs)

Question 11

Shape of carbon dioxide (CO2)

Answer 11

Linear (2 bonding groups, no lone pairs)

Question 12

Shape around each C in ethane (C2H6)

Answer 12

Tetrahedral (4 bonding groups, no lone pairs)

Question 13

Shape around each C in ethene (C2H4)

Answer 13

Trigonal planar (3 bonding groups, no lone pairs)

Question 14

What features make a molecule polar?

Answer 14

Polar bonds, arranged asymmetrically in the molecule

Question 15

Why is diamond hard?

Answer 15

4 strong covalent bonds per atom, arranged tetrahedrally

Question 16

Why doesn’t diamond conduct electricity?

Answer 16

As the valence electrons are fixed within bonds, there are no free-moving charged particles to move and carry charge

Question 17

Why is graphite soft?

Answer 17

The layers of carbon atoms can slide past each other easily

Question 18

Why can graphite conduct electricity?

Answer 18

Graphite contains delocalised electrons which can move and carry charge

Question 19

Why does PCl3 have a much higher boiling point than BCl3?

Answer 19

PCl3, a polar molecule, is able to form dipole-dipole forces and dispersion forces between molecules, whereas non-polar BCl3 is only able to form dispersion forces. As dipole-dipole forces are stronger than dispersion forces, it takes more energy to break the intermolecular forces between PCl3 molecules than BCl3 molecules

Question 20

Why does octane (C8H18) have a higher boiling point than pentane (C5H12)?

Answer 20

Because octane has more electrons than pentane (66 vs 42) and has a larger surface area between molecules, it is able to form stronger dispersion forces between molecules and requires more energy to disrupt these forces.

Question 21

Why does diamond have a much higher boiling point than water?

Answer 21

Diamond has strong covalent bonds between all of its atoms, which take lots of heat energy to disrupt. In comparison, the hydrogen bonds and dispersion forces between water molecules are relatively weak and can be disrupted using less energy.

Question 22

Why is the bond angle in ammonia (107) lower than that in methane (109.5)?

Answer 22

The lone pair in ammonia repels other valence shell electron pairs more effectively than the bonding pairs do. As a result, the bonding pairs in ammonia are pushed closer together than those in methane, which does not contain a lone pair.

Question 23

What three types of substance dissolve well in water?

Answer 23

Polar molecules, molecules that ionise, soluble ionic compounds

Question 24

What two properties affect the distance a component travels in paper chromatography or TLC?

Answer 24

Solubility in the mobile phase, and strength of adsorption to the stationary phase.

Question 25

What forces exist between the molecules of any hydrocarbon substance?

Answer 25

Dispersion forces (only)

Question 26

How does a dative covalent bond form?

Answer 26

Both shared electrons are contributed by one of the bonding atoms.

Question 27

How many lone pairs of electrons exist in hydrogen cyanide, HCN?

Answer 27

One (on the nitrogen - draw out the dot-cross diagram to be sure)

Question 28

Explain why tetrachloromethane, CCl4, is non-polar.

Answer 28

The four polar C-Cl bonds in CCl4 have polarities which cancel each other out as they are arranged symmetrically.

Question 29

Between what two molecules would a dispersion force arise?

Answer 29

Between an instantaneous dipole and an induced dipole

Question 30

Between what two molecules would a dipole-dipole force arise?

Answer 30

Between two permanent dipoles (polar molecules)

Question 31

Between what two molecules would a hydrogen bond arise?

Answer 31

Between one molecule containing H bonded to nitrogen/oxygen/fluorine, and another containing a delta-negative nitrogen/oxygen/fluorine.

Question 32

Why is buckminster fullerene (C60) considered a simple molecular substance?

Answer 32

The particles have a defined number of atoms (in this case, 60).

Question 33

Why are dispersion forces weaker than dipole-dipole forces?

Answer 33

Dispersion forces only arise between two temporary dipoles, so they are by nature temporary forces. On the other hand, dipole-dipole forces arise between permanent dipoles so they are much more permanent in nature.

Question 34

Not a question - be sure that you can draw any diagrams that appear in the topic, including those that show molecule shape, those that show bonding within and between molecules or ions, those that show structure of giant covalent substances etc.

Answer 34

I understand.

Question 35

Not a question - be sure that you can write balanced equations and ionic equations, as necessary, for any of the reaction types described during the topic.

Answer 35

I understand.