Properties of metals- CIE iGCSE Chemistry Notes - New Syllabus
Properties of metals for iGCSE Chemistry Notes
Core Syllabus
Compare the general physical properties of metals and non-metals, including:
(a) thermal conductivity
(b) electrical conductivity
(c) malleability and ductility
(d) melting points and boiling pointsDescribe the general chemical properties of metals, limited to their reactions with:
(a) dilute acids
(b) cold water and steam
(c) oxygen
Physical properties of metals and non-metals
Physical properties of metals and non-metals
(a) Thermal conductivity
Metals
They are generally good conductors of heat because they contain free-moving delocalised electrons in their metallic lattice. These electrons transfer kinetic energy quickly from the hotter part of the metal to the cooler part.
Non-metals
They are usually poor conductors of heat (insulators) because they lack delocalised electrons. Their particles are held by covalent bonds, and energy transfer occurs only by vibration, which is inefficient.
(b) Electrical conductivity
Metals
Metals are good conductors of electricity due to the presence of delocalised electrons that can flow freely through the metallic lattice when a potential difference is applied.
Non-metals
Non-metals are poor conductors (insulators) because they do not have delocalised electrons or mobile ions under normal conditions. Exceptions exist, such as graphite, which conducts electricity due to delocalised electrons between its layers.
(c) Malleability and ductility
Metals
Metals are malleable (can be hammered or rolled into sheets) and ductile (can be drawn into wires). This is because layers of positive metal ions in the metallic lattice can slide over one another without breaking the metallic bonds, as the delocalised electrons act as a “glue” holding the structure together.
Non-metals
Non-metals are usually brittle. When force is applied, their covalent or ionic structures tend to shatter instead of bending, as strong directional bonds break easily under stress.
(d) Melting points and boiling points
Metals
Metals generally have high melting and boiling points. This is because metallic bonding involves strong electrostatic attraction between positive metal ions and the sea of delocalised electrons, requiring large amounts of energy to overcome.
Non-metals
Non-metals usually have low melting and boiling points (many are gases at room temperature). They consist of small simple molecules held by weak intermolecular forces (van der Waals’ forces), which require little energy to break. Exceptions include giant covalent non-metals like diamond and graphite, which have very high melting points due to strong covalent bonds throughout their structures.
Example
Metals are good conductors of electricity while non-metals are poor conductors. Explain this difference using their structures.
▶️Answer/Explanation
Metals have a giant metallic structure with positive ions surrounded by a sea of delocalised electrons. These electrons are free to move and carry charge, so metals conduct electricity well.
Non-metals usually consist of simple covalent molecules without delocalised electrons, so they cannot conduct electricity. The exception is graphite, a form of carbon, which conducts because it has delocalised electrons between its layers.
General Chemical Properties of Metals
General Chemical Properties of Metals
Metals show characteristic chemical properties because they lose electrons to form positive ions. Their reactivity depends on their position in the reactivity series.
(a) Reaction with dilute acids
Metals above hydrogen in the reactivity series react with dilute acids to produce a salt and hydrogen gas.
The higher the metal in the series, the faster the reaction. Magnesium reacts vigorously, zinc moderately, and iron slowly. Copper, silver, and gold do not react.
General equation:
\( \text{Metal (s)} + \text{Acid (aq)} \rightarrow \text{Salt (aq)} + \text{H}_2 \text{(g)} \)
Example:
\( \text{Mg (s)} + 2\text{HCl (aq)} \rightarrow \text{MgCl}_2 \text{(aq)} + \text{H}_2 \text{(g)} \)
Hydrogen gas is identified by the characteristic “pop” sound with a lighted splint.
(b) Reaction with cold water and steam
Cold water:
Very reactive metals such as potassium, sodium, and calcium react with cold water to form a metal hydroxide and hydrogen gas.
General equation:
\( \text{Metal (s)} + \text{H}_2\text{O (l)} \rightarrow \text{Metal hydroxide (aq)} + \text{H}_2 \text{(g)} \)
Example:
\( 2\text{Na (s)} + 2\text{H}_2\text{O (l)} \rightarrow 2\text{NaOH (aq)} + \text{H}_2 \text{(g)} \)
Potassium reacts so vigorously that hydrogen may ignite with a lilac flame. Sodium reacts less violently, and calcium reacts more slowly, giving bubbles of hydrogen.
Steam:
Metals such as magnesium, zinc, and iron do not react with cold water but react with steam to form a metal oxide and hydrogen gas.
General equation:
\( \text{Metal (s)} + \text{H}_2\text{O (g)} \rightarrow \text{Metal oxide (s)} + \text{H}_2 \text{(g)} \)
Example:
\( \text{Mg (s)} + \text{H}_2\text{O (g)} \rightarrow \text{MgO (s)} + \text{H}_2 \text{(g)} \)
Magnesium reacts rapidly with steam, zinc more slowly, and iron only when strongly heated, forming a black solid mixture of oxides.
(c) Reaction with oxygen
Metals react with oxygen to form metal oxides. The speed and vigour of reaction depend on the reactivity of the metal.
General equation:
\( \text{Metal (s)} + \text{O}_2 \text{(g)} \rightarrow \text{Metal oxide (s)} \)
Example:
\( 2\text{Mg (s)} + \text{O}_2 \text{(g)} \rightarrow 2\text{MgO (s)} \)
Sodium and potassium tarnish quickly in air and are stored under oil. Magnesium burns with a bright white flame. Iron reacts slowly, producing rust in the presence of moisture and oxygen. Copper reacts only when heated strongly, forming black copper(II) oxide.
Most metal oxides are basic and neutralise acids. Some, such as aluminium oxide and zinc oxide, are amphoteric and react with both acids and bases.
Reactivity series connection
Potassium, sodium, calcium: very reactive, react with cold water, acids, and oxygen vigorously.
Magnesium, zinc, iron: moderately reactive, react with acids and steam, burn in oxygen when strongly heated.
Copper, silver, gold: unreactive, do not react with acids, water, or steam, but may react with oxygen at high temperatures (except gold).
Example
What happens when magnesium reacts with dilute hydrochloric acid?
▶️Answer/Explanation
Magnesium reacts with dilute hydrochloric acid to form magnesium chloride solution and hydrogen gas.
Equation: \( \text{Mg (s)} + 2\text{HCl (aq)} \rightarrow \text{MgCl}_2 \text{(aq)} + \text{H}_2 \text{(g)} \)
Hydrogen gas can be tested with a lighted splint, producing a “pop” sound.
Example
Describe the reaction of sodium with cold water.
▶️Answer/Explanation
Sodium reacts vigorously with cold water to form sodium hydroxide solution and hydrogen gas.
Equation: \( 2\text{Na (s)} + 2\text{H}_2\text{O (l)} \rightarrow 2\text{NaOH (aq)} + \text{H}_2 \text{(g)} \)
The sodium melts into a ball, moves quickly on the water surface, and hydrogen gas may ignite with a yellow flame.
Example
How does magnesium react with steam?
▶️Answer/Explanation
Magnesium reacts with steam to form magnesium oxide and hydrogen gas.
Equation: \( \text{Mg (s)} + \text{H}_2\text{O (g)} \rightarrow \text{MgO (s)} + \text{H}_2 \text{(g)} \)
The magnesium glows brightly in steam, producing a white powder of magnesium oxide.
Example
What is observed when iron reacts with oxygen in moist air?
▶️Answer/Explanation
Iron reacts slowly with oxygen and water in the air, forming hydrated iron(III) oxide (rust).
Equation: \( 4\text{Fe (s)} + 3\text{O}_2 \text{(g)} + 6\text{H}_2\text{O (l)} \rightarrow 4\text{Fe(OH)}_3 \text{(s)} \)
The brown, flaky rust weakens iron structures over time. This is a corrosion process rather than a fast reaction.