Covalent Bonds

Question 1

Between what do electrostatic attractions in a covalent bond occur?

Answer 1

A shared pair of electrons and the positively charged nuclei of the atoms involved in the bond.

Question 2

Electronegativity trend

Answer 2

Increase across a period, and up a group.

Question 3

Covalently bonded groups of atoms are called…

Answer 3

Molecules, not compounds

Question 4

What are some electron deficient elements?

Answer 4

B, Be, Mg, Al

Question 5

Increasing strength is 🤚👂…

Answer 5

Decreasing length

Question 6

The stronger a bond, the larger it’s

Answer 6

bond enthalpy

Question 7

Coordination bond

Answer 7

A shared pair of electrons which comes from one atom in a molecule.

Question 8

Explain the 180 degree bind in linear geometry compounds:

Answer 8

The electron domains repel each other equally

Question 9

Bond angle of trigonal planars?

Answer 9

120 degrees

Question 10

Explain the bond angle in NO2- being smaller than predicted:

Answer 10

The non-bonding pair of nitrogen exerts a stronger repulsion and therefore takes up more space.

Question 11

Tetrahedral Molecular geometry angle?

Answer 11

109.5

Question 12

Trigonal Pyramidal bond angle:

Answer 12

107

Question 13

Bent geometry (tetrahedral) angle:

Answer 13

104.5 degrees

Question 14

What causes bond polarity?

Answer 14

Differences in the electronegativities of the bonded atoms.

Question 15

Why is HF polar?

Answer 15

Fluorine has a much greater electronegativity, so it pulls the shared electron pair more strongly that hydrogen does.

Question 16

Dipole moment

Answer 16

The separation of charge between two non-identical bonded atoma.

Question 17

Why are some molecules non-polar?

Answer 17

Equal dipoles, no net dipole.

Question 18

Allotropes

Answer 18

Different Structural forms of the same element.

Question 19

Allotropes of carbon

Answer 19

Diamond, Graphite, Graphene and Fullerenes

Question 20

Diamond arrangement

Answer 20

Each c atoms bonded to 4 other c atoms in a tetrahedral arrangement.

Question 21

Diamond properties

Answer 21

• Hardest substances
• High refractive index and durability
• Poor electrical conductor as it has no mobile charged particles, all electrons are localized.
• Excellent thermal conductors: phonons travel well through highly regular lattice and strong covalent bonds.

Question 22

Graphite structure

Answer 22

Sheets of carbon atoms, each bonded to 3 others in a hexagonal arrangement, each C atom is triginal planar.

Question 23

Graphite’s properties

Answer 23

• Good electrical conductor, delocalized electrons are free to move in planes above and below each sheet.
• Good lubricant, LDFs between sheets are weak, while covalent bonds within are strong.

Question 24

Graphene properties

Answer 24

• Good electrical conductor
• Flexible, lightweight, transparent.

Question 25

Carbon nanotubes (nanotechnology):

Answer 25

• Strong due to covalent bonds holding c atoms together
• Good electrical conductors due to the presence of delocalized electrons.

Question 26

C60 has a…

Answer 26

Low boiling point because it doesn’t take much thermal energy to break the weak intermolecular forces.

Question 27

Silicon tetrahedral altitude structure properties:

Answer 27

• High strength, belting, and boiling points: extensive covalent bonds.
• Semiconductor.

Question 28

Silicon vs Carbon

Answer 28

• C= NM, S = Metalloid
  -Diamond = poor electrical conductor, Silicon = semi conductor
• C = Double/triple bonds, S = Single bonds

Question 29

Properties of SO2

Answer 29

• Hard, insoluble in water, high melting point.
• Poor conductor of heat and electricity in its solid crystalline form.

Question 30

London dipersion forces

Answer 30

Intermolecular forces resulting from from temporary instantaneous dipoles.

Question 31

What are the 2 main factors that increase the strenbth of LDFs?

Answer 31

Number of electrons and molecular shape, which affect the polarizability of the molecule, how easily the electron distribution is distorted.

Question 32

Explain the increasing boiling points down group 17

Answer 32

Larger molecules, so more electrons, more polarizability, stronger ldfs, more energy needed to break them up, higher boiling points.

Question 33

Dipole-induced dipole forces

Answer 33

Intermolecular force between a polar and non-polar molecule.

Question 34

Explain water boiling

Answer 34

At 100 celcius the energy is suffiicient to break hydrogen bonds, but not covalent bond between o and h.

Question 35

Group 14 boiling points trend down a group

Answer 35

Molecular mass increases, number of Es increases, increasing polarizability, stronger LDFs, inceasing boiling points.

Question 36

Why do large molecules have lower volatility and higher melting/boiling points?

Answer 36

Stronger LDFs

Question 37

Substances with covalent networks are

Answer 37

insoluble, strong covalent bonds

Question 38

Iodine properties

Answer 38

Non-polar, dissolves in non-polar solvents, insoluble in water.

Question 39

Evidence for benzene’s arrangement

Answer 39

• All c-c bonds have the same length
• Bond enthalpy of 210, the rest, 120, accounting for delocalization
• Only 1 isomer for 1,2-disubsistuted benzene , 2 would exist for present double bonds
• It would readily undergo addition reactions if it had double bonds.

Question 40

Why are are substances with covalent networks non-volatile and high in melting points?

Answer 40

• Strong covalent bonds holding the structure together.

Question 41

Why are covalent substances usually not electrical conductors?

Answer 41

• Covalent substances generally do not contain delocalized electrons as their electrons are localized in covalent bonds.

Question 42

What type of substance do photovoltaic cells contain?

Answer 42

Semiconductors, such as silicon.