Topic 4 Chemical Bonding and Structure (4.1, 4.2, 4.3, 4.4)

Question 1

4.1 What is the octet rule?

Answer 1

Noble gases have a full energy level of electrons and are stable because of it so atoms lose or gain electrons or share them to achieve electron configurations of noble gases

Question 2

4.1 What are some exceptions to the octet rule?

Answer 2

H, He, B, Be, and S are stable without 8 outer electrons

Question 3

4.1 What is the relationship between electronegativity difference and bonding?

Answer 3

0-0.4 non polar covalent, 0.5-1.7 polar covalent, >1.7 ionic

Question 4

4.1 How are ions formed?

Answer 4

Losing electrons would create positive ions (cations)
Gaining electrons would create negative ions (anions)
It is determined by the electron configuration- their valence electrons

Question 5

4.1 What is ionic bonding?

Answer 5

It is the electrostatic attraction between oppositely charged ions, occurring between metal and non-metals with a EN difference greater than 1.7 units.

Question 6

4.1 What are the properties of ionic compounds? 6 points

Answer 6

• They have a lattice structure help together by the oppositely charged ions
• Solid under standard conditions
• High mp and bp
• Low volatility
• Insoluble in non-polar substances
• Can’t conduct electricity in solid but aqueous solutions of ionic compounds can conduct

Question 7

4.1 How are ionic compounds dissolved?

Answer 7

Hydration: when ions leave the crystal and is surrounded by water molecules (oppositely charged ends of the compound attracts water, breaking the crystal into smaller pieces)
Dissociation: when ions separate from their crystal form, molecules completely broken into ions

Question 8

4.2 What is covalent bonding?

Answer 8

It is the electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Question 9

4.2 What are lewis structures?

Answer 9

It shows all the valence electrons in a molecule- the bonding and non-bonding electrons.

Question 10

4.2 What is the relationship between bond length and bond strength?

Answer 10

Decreasing length= increasing strength, triple bonds are the strongest because they are the shortest in length
Bonds in smaller atoms are also harder to break because the bonds are shorter in length

Question 11

4.2 What are pure covalent bonds?

Answer 11

Electrons are shared equally between the two atoms eg. H2, O2, Cl2, N2, CH4

Question 12

4.2 What are polar covalent bonds?

Answer 12

Unequal sharing of electrons results in a dipole- an imbalance of charge across the bond. Partial negative charge at the most electronegative atom, partial positive on the least

Question 13

4.2 How to identify polar covalent compounds? 3 points

Answer 13

Unsymmetrical, has lone pairs, elements around central atom is not the same

Question 14

4.2 What are allotropes and what are the 4 allotropes of carbon?

Answer 14

Different forms of the same element in the same physical state.
Diamond, graphite, fullerene C60, graphene

Question 15

4.2 Describe bonding, structure and properties of graphite.

Answer 15

C atoms are sp2 hybridised, covalent bonded to 3 others, forms hexagons in parallel layers with bond angles of 120 (van der waals’ forces between layers)
They are good electrical conductors but not thermal, soft and slippery, brittle, very high melting point.

Question 16

4.2 Describe bonding, structure and properties of diamond.

Answer 16

C atoms are sp3 hybridised, covalent bonded to 4 others, tetrahedrally arranged with bond angles of 109.5
They don’t conduct electricity but are thermal conductors, hard, brittle, very high melting point.

Question 17

4.2 Describe bonding, structure and properties of fullerene C60.

Answer 17

C atoms are sp2 hybridised, covalent bonded to 3 others, forms a sphere with 12 pentagons and 20 hexagons with bond angles of 120.
They are semi electrical conductors and low thermal conductors, light and strong, low melting point.

Question 18

4.2 Describe bonding, structure and properties of graphene.

Answer 18

Covalent bonded to 3 other carbons, forms hexagons with bond angles of 120.
They are good electrical and thermal conductors, very thin but strong, flexible, high melting point.

Question 19

4.2 What are resonance structures?

Answer 19

When there are more than one position for a double bond in a molecule. The bond lengths become equal, bond order is average of all the bonds present in the molecule.

Question 20

4.3 Outline the principles of the VSEPR theory

Answer 20

Find no. of electron pairs/ charge centres in valence shell of central atom, electron pairs repel each other and will therefore take up positions to minimise repulsions, non bonding pairs repel more than bonding pairs.

Question 21

4.3 Name all molecular geometry shapes, electron domains and their bond angles.

Answer 21

2 bonding pairs, 0 lone pairs linear 180
-
3,0 trigonal planar 120
2,1 bent <120
-
4,0 tetrahedral 109.5
3,1 trigonal pyramidal 107
2,2 bent 105
-
5,0 trigonal bipyramidal 90&amp;120
4,1 seesaw 90&amp;120
3,2 t shaped 90
2,3 linear 180
-
6,0 octahedral 90
5,1 square pyramidal 90
4,2 square planar 90

Question 22

4.3 What is the mnemonic for molecular geometry shapes? (:

Answer 22

LTBTTBTSTLOSS

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Question 23

4.3 What are coordinate covalent bonds/ dative covalent bonds?

Answer 23

Type of covalent bond where both electrons come from the same atom

Question 24

4.4 Difference between intermolecular and intramolecular, which one is weaker

Answer 24

Intermolecular- between molecules
Intramolecular- holds atoms together in a molecule
Intermolecular forces are generally weaker

Question 25

4.4 What are the different types of intermolecular forces?

Answer 25

London dispersion forces/ dipole induced force, dipole-dipole forces (both are van der waals’ forces), and hydrogen bonding

Question 26

4.4 What are london dispersion forces?

Answer 26

Electrons occupying positions that makes atoms form temporary dipoles. Only forces in non-polar molecules.

Question 27

4.4 What are dipole-dipole forces?

Answer 27

Attractive forces found between polar molecules- permanent dipoles (it can have both vdw forces).
Polar molecules have a partial negative charge on one end and a partial positive charge on the other end, attracting opposite charges.

Question 28

4.4 What is hydrogen bonding?

Answer 28

Special dipole-dipole forces between the slightly positive hydrogen atoms and a slightly negative atom/ electronegative atom- O, N or F.

Question 29

4.4 Arrange NH3, H2O and HF in order of increasing boiling points, give reason.

Answer 29

(least) NH3 > HF > H2O (most)
H2O can form 2 hydrogen bonds, HF higher than NH3 because F is more electronegative= stronger intermolecular hydrogen bonds