CHAPTER 4: METALLIC BONDING

Question 1

metallic properties (9)

Answer 1

• exhibit a range of melting points and relatively high boiling points
• good conductors of electricity
• good conductors of heat
• generally have high densities
• are malleable → can be shaped by beating or rolling
• are ductile → can be drawn into a wire
• are lustrous or reflective when first cut or polished
• are often hard with TENSILE strength → can resist a pulling force
• have low ionisation energies and electronegativities

Question 2

alkali metals

Answer 2

• soft enough to be cut with a knife
• react VIGOROUSLY with water to produce hydrogen gas

Question 3

forming metal ions

Answer 3

metal ions tend to lose their valence electrons to form positive ions called cations (octet rule → 8 electrons in valence shell)

Question 4

properties of transition metals

Answer 4

• tend to be harder and stronger
• have higher densities
• have higher melting points and boiling points
• some have strong magnetic properties
• high tensile strength
  
  • atoms of transition metals generally have a smaller size because of their greater core charge
  • allows them to pack together more tightly with stronger bonds
  • gives transition metals their properties
• transition metal compounds display a wide range of different colours
• exception: mercury is a liquid at room temperature
  
  • it can be called the noble gas of metals

Question 5

metallic bonding model

Answer 5

• positive ions are arranged in a lattice structure and occupy fixed positions
• negatively charged electrons move freely throughout the lattice
  
  • these electrons are called delocalised electrons because they belong to the lattice as a whole, rather than staying in the shell of a particular atom
• delocalised electrons come from the outer shells of the atoms
  
  • inner shell electrons are NOT free to move throughout the lattice and remain firmly bonded to the individual cations
• the positive cations are held in the lattice by the electrostatic force of attraction between these cations and the sea of delocalised elections
  
  • this attraction is known as the metallic bonding model

Question 6

explaining property: ‘metals are hard and have relative high boiling points’

Answer 6

strong electrostatic forces of attraction between positive metal ions and the sea of delocalised electrons holds the metallic lattice together

Question 7

explaining property: ‘metals are good conductors of electricity’

Answer 7

free moving delocalised electrons will move towards a positive electrode and away from a negative electrode in an electric circuit

Question 8

explaining property: ‘metals are malleable and ductile’

Answer 8

when a force causes metal ions to move past each other, layers of ions are still held together by the delocalised electrons between them

Question 9

explaining property: ‘metals generally have a high density’

Answer 9

• cations in a metal lattice are closely packed
  
  • the density of a metal depends on the mass of the metal ions, their radius, and the way in which they are packed

Question 10

explaining property: ‘metals are good conductors of heat’

Answer 10

when the delocalised electrons bump into each other, and into the metal ions, they transfer energy to their neighbours

Question 11

explaining property: ‘metals are lustrous’

Answer 11

because of the presence of free electrons in the lattice, metals reflect light of all wavelengths and appear shiny

Question 12

limitations of the metallic bonding model

Answer 12

• range of melting points, hardness and densities of different metals
• differences in electrical conductivities of metals
• magnetic nature of metals such as cobalt. iron and nickel

Question 13

reactivity of metals with water

Answer 13

• metals in group 1 are more reactive in water than those in group 2
• going down a group, the reactivity of the metal in water increases
• transition metals are generally less reactive with water than group 1 and group 2 metals are
• metal + water → metal hydroxide + hydrogen gas
  eg. 2Na + 2H2O → 2NaOH + 2H2

Question 14

reactivity of metals with acids

Answer 14

• the reactivity of different metals with acids follows the same general pattern as the reactivity of metals with water
• metals are normally more reactive with acids than with water
• metal + hydrogen chloride (HCl) -> metal chloride + hydrogen gas
  eg. Mg + 2HCl -> MgCl2 + H2

Question 15

reactivity of metals with oxygen

Answer 15

• the group 1 metal all react rapidly with oxygens
• the group 2 metals also react with oxygen to form oxides → not as rapidly as group 1 metals
• heat is usually required to start the reaction
• the transition metals are less reactive with oxygen than the metals in group 1 and group 2
• metal + oxygen gas (O2) → metal oxide
  eg. 4K + O2 → 2K2O

Question 16

reactivity series of metals

Answer 16

• the experimental results of metals reacting with water, acid and oxygen are used to place metals in order of reactivity called the reactivity series
• potassium
• sodium
• calcium
• magnesium
• aluminium
• zinc
• increasing reactivity ^

Question 17

ore

Answer 17

when the concentration of minerals in the rock are high enough to be economically extracted for use

Question 18

metal production from ores

Answer 18

mining

• surface/open pit mining
• underground mining
• in-situ leaching

ore processing
- ore is usually crushed into pebble-sized pieces or ground into a fine powder to separate the valuable minerals from the waste rock

metal extraction
- electrolysis: all metals can be extracted from their compounds by passing an electric current through the molten compound

• smelting: by heating it at high temperatures with carbon
• roasting: heat in air to convert metal sulfides → metal oxides

Question 19

environmental issues with metals

Answer 19

land

• clearing vegetation and erosion
• waste → long-term storage dumps, storage ponds

water

• large quantities of water are consumed
• toxic substances are released into groundwater and surface water

air

• CO2, SO2
• dust and particles

biodiversity

• decline in the number and variety of species in a given area

Question 20

metal recycling and circular economy

Answer 20

• linear economy: ‘Take-make-dispose’ or ‘Take-make-
  waste’ model
  raw materials → production → use → disposal
• circular economy: Economic systems that seeks to minimise climate change, waste, pollution and loss of biodiversity
  raw materials → production → use/reuse → recycling

Question 21

the recycling process of metals

Answer 21

• energy required to recycle metals is relatively a small fraction of the energy required to produce metals from ores
• scrap metals that come from 3 sources
  
  • waste from the initial manufacture and processing of metal
  • waste from the fabrication of the metals into products
  • the discarded metal-based product itself
• there are 4 steps involved in the recycling process
  
  1. collection
  2. preparation of recovery:
     
     • ferrous and non-ferrous metals are separated
     • metals need to be shredded as small pieces use
       less energy
  3. smelting: a secondary smelter is one designed for recycle metals
  4. purification

Question 22

alloys

Answer 22

• metals mixed with small amounts of another metal or
  carbon
• generally harder than a pure metal
• lower melting temperature than a pure metal

Question 23

what are crystals within a metal

Answer 23

a region within a solid where the particles are arranged in a regular way

Question 24

how does metal recycling contribute to a circular economy

Answer 24

• use less energy than extracting metals from their ores
• avoiding using metals as landill
• reduce co2 emmisions
• minimise impact of mining on land and water