Chapter 3 - Chemical Bonding

Question 1

Ionic bonds

Answer 1

Electrostatic forces of attraction between oppositely charged ions

Question 2

Structure of ionic compounds

Answer 2

Giant crystal lattice

• formed from the 3-dimensional regular packing of positive and negative ions
• bonded by strong electrostatic forces of attraction

Question 3

1. Ionic compounds have high melting and boiling points

Answer 3

• A large amount of heat energy is required to overcome the strong forces of attraction between the oppositely-charged ions

Question 4

2. Ionic compounds are soluble in water but insoluble in organic solvents

Answer 4

• Water molecules are polar molecules → form electrostatic forces with the ions, causing ions to separate and dissolving the compound
• Organic solvents are non-polar molecules which cannot attract the ions and are hence unable to dissolve the compound.

Question 5

Organic solvents (examples)

Answer 5

• hexane
• ethanol
• turpentine
• petrol

Question 6

3. Ionic compounds do not conduct electricity in solid but conduct electricity in molten or aqueous state

Answer 6

• Solid state → ions are fixed within the crystal lattice and only vibrate about the lattice points
• Molten/Aqueous state → ions are free to move (mobile) and can act as charge carriers to conduct electricity

Question 7

4. Ionic compounds are brittle and shatter when hit

Answer 7

• When the lattice is hit, a layer of ions is shifted so that ions with the same charges are lined up together
• These like charges repel each other and split the ionic lattice

Question 8

Covalent bonds

Answer 8

Electrostatic forces of attraction between the positive nuclei of the 2 atoms and the bonding electrons shared between them

Question 9

Chemical formula of methane

Answer 9

CH4

Question 10

Chemical formula of hydrogen peroxide

Answer 10

H2O2

Question 11

Structure of simple molecules (covalent)

Answer 11

• Simple discrete molecules at lattice points
• Atoms of the molecules are held by strong covalent bonds
• Weak intermolecular forces (van der waals forces/hydrogen bonds) between the molecules

Question 12

Hydrogen bonds

Answer 12

• H directly bonded to N (nitrogen), O (oxygen) or F (fluorine)
• Stronger than van der waals forces

Question 13

Structure of macromolecules (covalent)

Answer 13

• Atoms at lattice points that can be extended infinitely in 3 dimensions to form a giant lattice

Question 14

Allotrope

Answer 14

Solid forms of an element with different molecular structures

Question 15

Diamond (structure)

Answer 15

• Each C atom forms 4 single covalent bonds with 4 other C atoms
• Tetrahedral arrangement

Question 16

Graphite (structure)

Answer 16

• Each C atom forms 3 single covalent bonds with 3 other C atoms
• The 4th unpaired valence electron of each C atom is delocalised along the layers
• Layers are held by weak van der waals forces
• Hexagonal arrangement (flat, parallel layers)

Question 17

1. Simple molecules have low melting and boiling points

Answer 17

• A small amount of heat energy is required to overcome the weak intermolecular forces of attraction between molecules

Question 18

2. Simple molecules are generally soluble in organic solvents and insoluble in water

Answer 18

• Exceptions: HCl (hydrogen chloride) exist as simple discrete molecules in organic solvents but ionises in water to form H+ and Cl-

Question 19

3. Simple molecules do not conduct electricity in any state

Answer 19

• There are no mobile charged particles (delocalised electrons/mobile ions) to carry charges
• Exceptions: HCl (hydrogen chloride) ionises in water to form acidic solutions with mobile H+ and Cl- ions which conduct electricity

Question 20

4. Simple molecules are generally soft

Answer 20

• A small amount of energy is required to break and deform the weak intermolecular forces between molecules

Question 21

1. Macromolecules have high melting and boiling points

Answer 21

• A large amount of heat energy is required to overcome the strong covalent bonds between atoms in the molecules

Question 22

2. Macromolecules are insoluble in all solvents

Answer 22

• A large amount of energy is required to overcome the strong covalent bonds between atoms

Question 23

3. Macromolecules do not conduct electricity in any state

Answer 23

• Substances made up of neutral atoms and do not contain mobile charge particles (delocalised electrons/mobile ions) to carry charges
• Exceptions: Graphite is a good conductor of electricity due to the presence of delocalised electrons along the layers to conduct electrcity

Question 24

4. Macromolecules are generally hard

Answer 24

• A large amount of energy is required to break and deform the strong covalent bonds between the atoms
• Exceptions: Graphite is soft as layers are held by weak van der waals forces

Question 25

Metallic bonds

Answer 25

Strong electrostatic attraction between positive metal ions and negative delocalised ions (mobile valence electrons of the metal)

Question 26

Structure of metallic compounds

Answer 26

Giant metallic structure

• a lattice of bonded positive metal ions
• surrounded by a ‘sea of mobile electrons’

Question 27

What are factors affecting the strength of metallic bonds?

Answer 27

1. Number of valence electrons

2. Size of metal ions

Question 28

1) Number of valence electrons

Answer 28

• As the number of valence electrons increases, the charge of the positive metal ion increases
• The number of delocalised electrons increases which then increases the strength of the metallic bond

Question 29

2) Size of metal ions

Answer 29

• The smaller the metal ions, the closer the positive nuclei to the delocalised electrons
• This results in a greater electrostatic attraction between the positive nuclei and the delocalised electrons → stronger metallic bonds

Question 30

1. Metals have high melting and boiling points

Answer 30

• A large amount of energy is required to overcome the strong electrostatic forces of attraction between positive metal ions and the negative delocalised electrons

Question 31

2. Metals are generally insoluble in water and organic solvents

Answer 31

• Exceptions: Reactive metals such as sodium and potassium can react with water to give hydrogen gas

Question 32

3. Metals are good conductors of electricity

Answer 32

• In the solid and molten states, delocalised electrons rapidly carry charges through the metal lattice

Question 33

Electrical conductivity increases with greater number of ________

Answer 33

valence electrons

Question 34

3. Metals are good conductors of heat

Answer 34

• When a metal is heated, delocalised electrons gain kinetic energy and moves faster to transfer the gained energy throughout the metal
• Heat travels through the metal lattice as a result of rapid movement of delocalised electrons

Question 35

Define “malleable”

Answer 35

Can be hammered into different shapes without breaking

Question 36

Define “ductile”

Answer 36

Can be drawn into wires without breaking

Question 37

4. Metals are malleable and ductile

Answer 37

• Layers of atoms can slide over one another without breaking the strong metallic bonds