2.2 - The Covalent Model

Question 1

State the octet rule.

Answer 1

The Octet rule states that atoms bond together in order to achieve a full valence shell containing 8 electrons.

Question 2

How does covalent bonding work?

Answer 2

Atoms share electrons to achieve a full outer shell.

Question 3

List the 5 exceptions to the octet rule.

Answer 3

Question 4

What type of elements does covalent bonding occur between?

Answer 4

Non-metals.

Question 5

State the rough conditions of electronegativity difference for non-polar covalent, polar covalent, and ionic bonds.

Answer 5

Question 6

Describe a covalent bond.

Answer 6

The electrostatic attraction between positive nuclei and shared pair of electrons.

Question 7

Describe the difference between single covalent to multiple covalent.

Answer 7

Single bonds are weaker and longer than double or triple bonds.

Question 8

What is a coordinate covalent bond?

Answer 8

A bond where one atom contributes both the bonding electrons.

Question 9

Name an example of a coordinate covalent bond.

Answer 9

Carbon Monoxide.

Question 10

What is the difference between regular covalent bonds and coordinate covalent bonds?

Answer 10

Once a coordinate covalent bond is formed, it is identical to a regular covalent bond.

Question 11

Complete the table: |Electron domain|Bonding domain|Lone pair|Electron domain geometry|Molecular geometry|Bond angle|Example|

There should be 6 rows, for 2-4 electron domains

Answer 11

Question 12

State the rough conditions of electronegativity difference for non-polar (pure) covalent, polar covalent (weak polar), and polar covalent.

Answer 12

Question 13

Which atom is the partial negative charge assigned to in a polar molecule?

Answer 13

The more electronegative atom

Question 14

What is the sharing of electrons in non-polar covalent bonds?

Answer 14

Equal sharing of electrons

Question 15

What is the sharing of electrons in polar covalent bonds?

Answer 15

Unequal sharing of electrons

Question 16

What is the sharing of electrons in ionic bonds?

Answer 16

No sharing of electrons.

Question 17

What two conditions does the polarity of a molecule depend on?

Answer 17

• The presence of polar bonds in the molecule
• The geometry of the molecule

Question 18

What do polar molecules have?

Answer 18

A net dipole moment

Question 19

What two forms do covalent substances have?

Answer 19

• Individual molecules
• Giant covalent structures

Question 20

What do giant covalent structures not have that individual molecules have?

Answer 20

Intermolecular forces

Question 21

What phase are molecular compounds often in when in room temperature? Why?

Answer 21

Gases or liquids due to weak intermolecular forces.

Question 22

What phase are giant covalent often in when in room temperature? Why?

Answer 22

Solid, as they have high melting and boiling points due to strong covalent bonds.

Question 23

Detail out the solubility and conductivity of both molecular elements/compounds and giant covalent structures.

Answer 23

Question 24

Define allotrope

Answer 24

Different forms of the same element in the same physical state.

Question 25

List the 4 allotropes of carbon

Answer 25

Graphite, Diamond, Fullerene C60, Graphene

Question 26

List some features of graphite

Answer 26

- Layered structure - Layers held together by weak intermolecular forces - Each carbon is bonded to 3 others - Trigonal planar bond - Good conductor of electricity due to delocalized electrons

Question 27

List some features of diamond

Answer 27

- Giant covalent structure - High melting and boiling point - Each carbon is bonded to 4 others, tetrahedral structure - Not conductive

Question 28

List some features of fullerene C60

Answer 28

- 12 pentagons and 20 hexagons - Each carbon is connected to 3 others - Trigonal planar structure - Conductive but less so than graphite or graphene

Question 29

List some features of graphene

Answer 29

- Very thin - one layer; but very strong - Each carbon bonded to 3 other carbons - Trigonal planar - High conductivity -

Question 30

Define intermolecular forces

Answer 30

Forces between two molecules that determine the physical properties such as melting point and boiling point.

Question 31

List the order of the 3 intermolecular forces, weakest to strongest

Answer 31

London dispersion, dipole-dipole, hydrogen bonding

Question 32

Explain london dispersion forces

Answer 32

Caused by the movement of electrons creating instantaneous dipoles and induced dipoles

Question 33

What do london dispersion forces increase with?

Answer 33

Molar mass

Question 34

Do all atoms have london dispersion forces?

Answer 34

Yes

Question 35

Explain dipole-dipole forces

Answer 35

Occurs between polar molecules, it is the electrostatic attraction between opposite partial charges on two molecules

Question 36

What do dipole-dipole forces increase with?

Answer 36

Dipole moment

Question 37

Explain hydrogen bonding

Answer 37

Dipole-dipole forces between hydrogen and nitrogen, oxygen, fluorine.

Question 38

What is a polar solvent

Answer 38

A liquid containing polar molecules

Question 39

What are polar and non-polar substances soluble in?

Answer 39

Polar in polar solvents and non-polar in non-polar solvents

Question 40

Explain ion-dipole forces

Answer 40

They occur between water molecules and ions in aqueous solutions, ions and oppositely charged dipoles on the water molecules bond, water molecules surround the ions creating a hydrogen shell.

Question 41

Why are most ionic compounds soluble in water?

Answer 41

Due to ion-dipole forces

Question 42

Why are polar substances soluble in water?

Answer 42

Due to hydrogen bonds

Question 43

Why are non-polar substances soluble in non-polar solvents (such as oil and hexane)?

Answer 43

Due to london dispersion forces

Question 44

What conditions must a substance meet for it to be conductive?

Answer 44

Delocalised electrons or free moving ions

Question 45

Discuss the conductivity of covalent structures

Answer 45

Poor conductivity due to lack of free electrons, graphite is an exception

Question 46

Discuss the conductivity of ionic compounds

Answer 46

Only conductive when melted due to free moving ions

Question 47

Discuss the conductivity of metallic substances

Answer 47

Conductive due to sea of electrons

Question 48

Retention factor formula

Answer 48

Question 49

When do resonance structures occur?

Answer 49

When there is more than one position for a multiple-bond in a molecule

Question 50

What is a resonance hybrid structure?

Answer 50

The real structure that is in a resonance structure, the length and strength of the bonds are between single and double and the electrons are delocalized/shared

Question 51

What are π electrons

Answer 51

The delocalized electrons in resonance structures

Question 52

What are two pieces of evidence for the structure of benzene?

Answer 52

- Enthalpy for the hydrogenation of benzene is lower than predicted - Benzene undergoes substitution rather than addition reactions

Question 53

Complete the table: |Electron domain|Bonding domain|Lone pair|Electron domain geometry|Molecular geometry|Bond angle| There should be 6 rows, for 5-6 electron domains

Answer 53

Question 54

Formal charge formula

Answer 54

Question 55

Define formal charge

Answer 55

The charge an atom would have if all of the atoms in a molecule had the same electronegativity.

Question 56

What gets prioritised when formal charge is the same

Answer 56

The molecule with the more electronegative atom having the negative charge.

Question 57

How does the formal charge calculation change for ions?

Answer 57

The sum of the formal charge must equal the charge on the ion

Question 58

How is a sigma bond formed

Answer 58

The head on overlap of an s orbital and/or a p orbital

Question 59

How is a pi bond formed

Answer 59

The sideways overlap of two p orbitals

Question 60

List the types of overlaps and the bonds formed

Answer 60

Question 61

List the types of bonds and the number of sigma and pi bonds that correspond to them

Answer 61

Question 62

List out the number of electron domains and the corresponding hybridisation for them

Answer 62

Question 63

What is hybridisation

Answer 63

The mixing of atomic orbitals to produce hybrid orbitals for bonding. 2s electron gets promoted to 2p