Metals and Their Compounds – SS3 Chemistry Lesson Note (First Term)

Metals are elements that lose electrons easily to form positive ions (cations).

• Bonding: metal atoms are held together by metallic bonding.
• With nonmetals: metals form ionic compounds.
• With acids: metals react to give a salt and hydrogen gas.

Behavioural objectives

By the end of the lesson, students should be able to:

1. Explain the general characteristics of metals.
2. Identify the parts of the periodic table containing metals.
3. Show on charts the relative abundance of metals in nature.
4. Describe the extraction processes of metals.
5. Identify the general properties of alkali metals.

Instructional techniques

• Identification
• Explanation
• Questions and answers
• Demonstration
• Videos from source

Instructional materials

• Samples of metals and their compounds
• Periodic table of elements
• Charts of mineral ore distribution in Nigeria

Where are metals found in the periodic table?

Metals occupy the left and centre of the periodic table, and nonmetals occupy the upper right.

• Group 1 (alkali metals): lithium, sodium, potassium and others, on the far left.
• Group 2 (alkaline earth metals): magnesium, calcium and others, next to Group 1.
• Transition metals: the central block, including iron, copper, zinc and silver.
• Metals after the transition block: aluminium, tin and lead.
• Metalloids: elements along the dividing “staircase” line, with properties between metals and nonmetals.

What are the physical characteristics of metals?

Most metals are hard, shiny solids that conduct heat and electricity.

• Lustre: they have a shiny surface when freshly cut or polished.
• Conductivity: they conduct heat and electricity well.
• Malleability: they can be hammered into sheets.
• Ductility: they can be drawn into wires.
• Melting point: most have high melting and boiling points. Mercury is a liquid at room temperature.

What are the chemical characteristics of metals?

Metals are chemically characterised by the ease with which they lose electrons.

1. Cation formation: metals lose electrons easily to form positive ions. This links to their position on the left of the periodic table.
2. Metallic bonding: electrons are delocalised and move freely among the metal atoms. This explains conductivity and malleability.
3. Oxidation: metals lose electrons when they react. The easier they lose electrons, the more reactive they are. Alkali metals oxidise readily.
4. Ionic compounds: a metal gives electrons to a nonmetal, forming positive metal ions and negative nonmetal ions.
5. Reaction with acids: metals above hydrogen in the reactivity series react with acids to give hydrogen gas and a salt. Some react more vigorously than others.

What are the common compounds of metals?

Metals form oxides, hydroxides, chlorides, sulphides and carbonates, among other compounds.

1. Metal oxides: metals react with oxygen to form oxides. Iron forms iron(III) oxide, the main part of rust (rust also needs water).
   4Fe + 3O₂ → 2Fe₂O₃
2. Metal hydroxides: reactive metals react with water to form hydroxides. Sodium gives sodium hydroxide and hydrogen gas.
   2Na + 2H₂O → 2NaOH + H₂
3. Metal chlorides: metals react with chlorine to form chlorides. Sodium gives sodium chloride.
   2Na + Cl₂ → 2NaCl
4. Metal sulphides: metals combine with sulphur to form sulphides. Zinc gives zinc sulphide.
   Zn + S → ZnS
5. Metal carbonates: metal ions react with carbonate ions to form carbonates. Calcium ions give calcium carbonate.
   Ca²⁺ + CO₃^2- → CaCO₃

How abundant are metals in nature?

Aluminium is the most abundant metal in the Earth’s crust, followed by iron.

• Order of abundance in the crust: aluminium, iron, calcium, sodium, potassium, magnesium.
• Occurrence: most metals occur as compounds (ores) in rocks. Gold and a few others occur native (uncombined).
• Ore: a mineral from which a metal can be extracted at a profit.

• Nigerian examples: tin ore on the Jos Plateau, limestone at Ewekoro and iron ore at Itakpe.

What are the principles of extraction of metals?

The method used to extract a metal depends on its position in the reactivity series.

What is extraction by electrolysis?

Electrolysis is the use of electric current to break down a molten metal compound into the metal and another product.

• Use: for reactive metals such as sodium, magnesium and aluminium, which carbon cannot reduce.
• At the cathode (-): metal ions gain electrons and form the metal.

What is extraction by reduction of oxides?

Reduction of an oxide is the removal of oxygen from a metal oxide to leave the metal.

• Reducing agent: carbon (coke) or carbon monoxide.
• Simplified equation for iron: 2Fe₂O₃ + 3C → 4Fe + 3CO₂

In the blast furnace, the main steps are:

1. Coke burns in hot air to form carbon dioxide: C + O₂ → CO₂
2. Carbon dioxide reacts with more coke to form carbon monoxide: CO₂ + C → 2CO
3. Carbon monoxide reduces the iron(III) oxide: Fe₂O₃ + 3CO → 2Fe + 3CO₂
4. Limestone is added to remove impurities as slag.

What is extraction by reduction of chlorides?

Some metals, such as titanium, are made by reducing their chloride with a more reactive metal.

• Reducing agent: magnesium (sodium has also been used).
• Equation for titanium: TiCl₄ + 2Mg → 2MgCl₂ + Ti

What is a displacement reaction?

A displacement reaction is one in which a more reactive metal takes the place of a less reactive metal in its compound.

• Example: aluminium displaces iron from iron(II) sulphate solution.
  3FeSO₄ + 2Al → Al₂(SO₄)₃ + 3Fe
• Note: this shows relative reactivity. It is not the industrial method for making iron.

What are alkali metals?

Alkali metals are the elements of Group 1 of the periodic table: lithium, sodium, potassium, rubidium, caesium and francium.

• Soft and shiny: they can be cut with a knife and look shiny when freshly cut.
• Low density: they are light compared with other metals.
• Low melting and boiling points: they melt and vaporise easily for metals.
• Good conductors: they conduct heat and electricity.
• Highly reactive: they have one outer electron, which they lose easily to form a +1 ion.
• Ionic compounds: they readily form ionic compounds with nonmetals, especially halogens.
• Reactivity trend: reactivity increases down the group.
• Storage: they are kept under oil (such as kerosene) to keep out air and moisture.
• Hydroxides: they react with water to form strongly alkaline hydroxides, which gives the group its name.

What is sodium?

Sodium (Na) is a soft, silvery-white alkali metal in Group 1, with atomic number 11.

How is sodium extracted?

Sodium is extracted by the electrolysis of molten sodium chloride (NaCl) in the Downs Cell.

The key steps are:

1. Melting the salt: sodium chloride is melted. Calcium chloride is usually added to lower the melting point.
2. Setting up the cell: the molten NaCl is placed in the Downs Cell, which has a graphite anode and an iron cathode.
3. Passing current: sodium ions move to the cathode and chloride ions move to the anode.
4. At the cathode: sodium ions gain electrons and are reduced to sodium metal.
   Na⁺ + e^– → Na
5. At the anode: chloride ions lose electrons and are oxidised to chlorine gas.
   2Cl^– → Cl₂ + 2e^–
6. Collecting sodium: sodium is less dense than the molten salt, so it rises to the surface and is collected.
7. Collecting chlorine: chlorine gas leaves at the anode and is collected separately.

What are the properties of sodium?

Sodium is a soft, low-density, very reactive metal that colours a flame yellow.

Physical properties

• Appearance: soft, shiny, silvery-white metal that tarnishes quickly in air.
• Density: low density.
• Melting point: low, at 97.8°C (208°F).

Chemical properties

• Reactivity: it reacts vigorously with water to give sodium hydroxide and hydrogen gas.
• Oxidation state: it shows +1 in its compounds.
• Compounds: it forms sodium chloride (table salt) and sodium hydroxide (a strong base).

Flame test

• Result: sodium compounds give a yellow flame.

What are the uses of sodium and its compounds?

Sodium and its compounds are used in industry, metal extraction, water treatment and food.

• Soap and chemicals: sodium hydroxide (NaOH) is used to make soaps, detergents and other chemicals.
• Glass, paper and textiles: sodium carbonate (Na₂CO₃), called soda ash, is used in their production.
• Metal extraction: sodium can act as a reducing agent in making some metals, such as titanium.
• Water treatment: sodium hypochlorite (NaClO) is in bleach and is used as a disinfectant.
• Food: table salt (NaCl) flavours and preserves food.

Evaluation

1. Identify the parts of the periodic table containing metals.
2. Mention five characteristics of metals.
3. Name three compounds of metals and give one example of each.
4. Name the most abundant metal in the Earth’s crust and give two ores with their formulae.
5. State four uses of sodium and its compounds.

Assignment

Describe how sodium is extracted from molten sodium chloride in the Downs Cell. Include the equation at each electrode and the equation for the reaction of sodium with water.