Chapter 3 - reactions of metals

Metallic Bonding and Properties of Metals

Metallic Bonding

• Metals are extracted from ores found in the Earth’s crust.

• Metals possess low ionization energies, requiring minimal energy to remove valence electrons.

• Metal atoms lose valence electrons to form cations.

• Metallic bonding involves the electrostatic attraction between delocalized electrons and cations in a metallic lattice structure.

• Delocalized electrons move freely between metal cations.

• Metallic bonding is non-directional; electrostatic forces act in all directions.

• The strength of metallic bonding arises from the electrostatic attraction between delocalized electrons and the cation lattice.

• Limitations of the metallic bonding model:

  • Does not explain different melting and boiling points of metals.

  • Does not explain differences in electrical conductivity of metals.

  • Does not explain magnetic properties of iron, nickel, and cobalt.

Metallic Bonding Model

• Metal atoms lose valence electrons, forming a sea of delocalized electrons.

• These delocalized electrons are electrostatically attracted to the cation lattice.

  

Properties of Metals

• Malleability: Metals can be shaped without breaking due to delocalized electrons moving alongside the cation lattice.

• Ductility: Metals can be drawn into thin wires because delocalized electrons are free to move towards a positive electrode.

• Electrical Conductivity: Metals allow the flow of charge because electrons are attracted to a positive electrode in an electric circuit.

• Heat Conductivity: When metal absorbs heat, the kinetic energy of delocalized electrons and cations increases. Cations vibrate rapidly, and delocalized electrons transfer kinetic energy, creating a chain reaction.

• High Melting and Boiling Points: Metals can withstand high temperatures.

• Lustre: Metals are shiny and reflective due to delocalized electrons at the surface reflecting light.

Lustre Explanation

• Delocalized electrons constantly move across the cation lattice.

• Light rays falling on delocalized electrons are reflected, giving a lustrous appearance.

Reactions of Metals

Reactions with Acids

• Metals react with acids to varying degrees due to their lower ionization energies.

• Loss of electrons during the reaction is called oxidation.

• General reaction: acid + reactive metal → ionic salt + hydrogen gas

• H_2 gas can be detected using the ‘hydrogen pop test’.

• Ionic compounds (salts) contain one or more cations and anions.

• Qualitative signs of a chemical reaction (COBALT): Colour, Odour, Bubbles, Appearance/disappearance of solid, Light/sound, Temperature change

Example Reaction

• zinc + nitric acid → zinc nitrate + hydrogen gas

• Zn(s) + 2HNO3(aq) → Zn(NO3)2(aq) + H2(g)

Reactions with Water

• Group 1 and Group 2 metals react with water.

• General reaction: water + reactive metal → metal hydroxide + hydrogen gas

• Phenolphthalein indicates the presence of hydroxide ions.

• Group 1 metals react explosively with water.

• Going down a group lowers ionization energy.

Example Reaction

• lithium + water → lithium hydroxide + hydrogen gas

• 2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)

Reactions with Oxygen

• Many metals react with oxygen.

• General reaction: metal + oxygen → metal oxide

• The loss of electrons is called oxidation; corrosion of iron is called rusting.

Example Reaction

• magnesium and oxygen: 2Mg(s) + O_2(g) → 2MgO(s)

*Example showing aluminium forming a protective layer with oxygen.

• aluminium + oxygen → aluminium oxide

• 4Al(s) + 3O2(g) → 2Al2O_3(s)

Reactivity Series

• Metals vary in their ability to react with oxygen. Some do not react under normal conditions, while others react to form oxides.

Metal Recycling and Circular Economy

Circular Economy

• Transition from a linear economy (take-make-dispose) to a circular economy (continuous cycle of resource use and re-use).

• Circular economy focuses on optimal use and reuse of resources, from raw material extraction to repurposing waste materials.

Green Chemistry Principles

• Four principles related to a circular economy:

  • Atom economy: maximize incorporation of reactant materials into the final product.

  • Design for energy efficiency: minimize negative environmental and economic impacts.

  • Prevention of wastes: prevent waste rather than treating it later.

  • Use of renewable feedstocks: use renewable materials instead of fossil fuels.

Metal Recycling Steps

• Mining: extract natural resources.

• Refining: prepare metal for use.

• Made into a product: manufacturing.

• Used: product consumption.

• Disposed of via recycling: waste management.

• Reprocessed as the same original product: reuse materials.

• Repurposed as a new product: create new products from waste.

Alloys

• An alloy is a mixture of elements, mainly metals.
  bronze: copper, tin
  brass: copper, zinc
  steel: iron, carbon, chromium

Benefits of Recycling

• Most metals can be recycled an unlimited number of times

• Example metal energy savings: aluminium (95%), nickel (90%), copper (84%).