S2.3 The metallic model

Question 1

metallic bond

Answer 1

the electrostatic attraction between a lattice of cations and sea of delocalised electrons

Question 2

electrical conductivity of metals

Answer 2

• Conduct when solid or liquid, mobile electrons which can freely move and conduct
• When PD is applied to a metal lattice, delocalised electrons repel away from negative terminal and move to positive terminal
• Across a period, number of electrons increases, number of delocalised electrons increases, so electrical conductivity also increases
• Bonding is non-directional, so it doesn’t matter how the cations are oriented relative to each other

Question 3

thermal conductivity of metals

Answer 3

• Good thermal conductors due to cation behaviour and their delocalised electrons
• When heated, cations in the lattice vibrate more vigorously as thermal energy increases
• The vibrating cations transfer kinetic energy as they collide with neighbouring cations, conducting heat effectively
• Delocalised electrons are not bound to a specific atom so are free to move
• The cations transfer kinetic energy to electrons when they vibrate
• The delocalised electrons carry the increased kinetic energy and transfer it rapidly throughout the metal
• This contributes to the high thermal conductivity

Question 4

malleability of metals

Answer 4

• Metals are malleable
• When a force is applied, the metal layers can slide, as the metals are arranged in layers
• When layers slide, metallic bonds reform, this is because attractive forces between metal ions and electrons act in all directions
• The lattice isn’t broken and has changed shape

Question 5

strong and hard (property of metals)

Answer 5

• Strong attractive forces between metal ions and delocalised electrons

Question 6

high MP and BP of metals

Answer 6

• Due to strong electrostatic forces of attraction between cations and delocalised electrons in the metallic lattice
• These need lots of energy to overcome MP and BP increase across a group due to stronger electrostatic forces (charge increases)

Question 7

what does the strength of a metallic bond depend on

Answer 7

• charge of the ions
• radius of the metal ion

Question 8

explain how the charge of the ion influences the strength of the metallic bond

Answer 8

• Greater charge → greater number of electrons in the delocalised ‘sea’ → greater charge difference between the ions and electrons
• Greater charge difference → stronger electrostatic attraction → stronger metallic bond
• Across a period, the charge increases while the radii is kept constant, so the MP/BP increases

Question 9

explain how the radius of the metal ion influences the strength of the metallic bond

Answer 9

• Smaller ionic radii → exert a greater attraction on the sea of delocalised electrons
• Greater attraction → stronger metallic bond → more energy is needed to break this
• Down a group, the radius increases while the charge is kept constant, so the MP/BP decreases

Question 10

how to increase electrostatic attraction

Answer 10

• Increase the number of delocalised electrons per metal atom
• Increase the number of positive charges on metal centres in the lattice
• Decrease the size of metal ions

Question 11

what occurs down a group (to MP and BP)

Answer 11

• cation size increases
• so there is a decreases attraction between the outer electron and metallic lattice
• decreasing MP/BP

Question 12

what occurs across a period (to MP and BP)

Answer 12

• the charge increases
• stronger metallic bonding, more energy is needed to break the metallic lattice
• increasing MP/BP