CIE iGCSE Co-ordinated Sciences-C9.1 Properties of metals- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-C9.1 Properties of metals – Study Notes
CIE iGCSE Co-ordinated Sciences-C9.1 Properties of metals – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- 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 points - Describe the general chemical properties of metals, limited to their reactions with:
(a) dilute acids
(b) cold water and steam
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Properties of Metals: Comparison with Non-Metals
Metals and non-metals exhibit contrasting physical properties due to differences in atomic structure, bonding, and electron arrangement. Understanding these differences is essential in predicting behaviour in practical and chemical contexts.
Comparison of Physical Properties:
Thermal conductivity:
Metals are excellent conductors of heat. This is due to delocalised electrons in the metallic lattice, which can transfer kinetic energy rapidly between atoms. Non-metals are generally poor conductors of heat because they lack free electrons, and energy transfer occurs only through vibration of atoms or molecules.
Electrical conductivity:
Metals conduct electricity because their delocalised electrons are free to move through the lattice when a potential difference is applied. Non-metals do not conduct electricity in solid or liquid form as they have no mobile charge carriers. An exception is graphite, where delocalised electrons in layers allow conductivity.
Malleability and ductility:
Metals are malleable (can be hammered or rolled into sheets) and ductile (can be drawn into wires) because the metallic bonding allows layers of positively charged ions to slide over each other without breaking the metallic bonds. Non-metals are brittle: when force is applied, they fracture easily because their directional covalent or molecular bonds cannot shift.
Melting points and boiling points:
Metals generally have high melting and boiling points due to strong metallic bonds, which require a large amount of energy to break. Non-metals often have lower melting and boiling points because they are held together by weak van der Waals forces in molecular solids or have relatively weaker covalent bonds in their lattice (exceptions include diamond and silicon).
Additional Notes:
- Density: Metals usually have high densities due to closely packed atoms in metallic crystals. Non-metals have lower densities, often being gases or light solids.
- Lustre: Metals are shiny (metallic lustre) when freshly cut, while non-metals are dull.
Example
Compare copper (Cu) and sulfur (S) in terms of thermal and electrical conductivity.
▶️Answer/Explanation
Copper is a metal with delocalised electrons, so it efficiently transfers both heat and electric current. Sulfur is a non-metal composed of S₈ molecules; it has no free electrons, so it is a poor conductor of heat and electricity.
Example
Explain why iron (Fe) is malleable and phosphorus (P) is brittle.
▶️Answer/Explanation
Iron atoms are arranged in a metallic lattice with delocalised electrons, allowing layers of atoms to slide over each other without breaking bonds, making it malleable and ductile. Phosphorus forms a covalent molecular lattice (P₄ tetrahedra in white phosphorus) that is rigid; applying force breaks the covalent bonds, making it brittle.
Example
Compare the melting points of metals and non-metals.
▶️Answer/Explanation
Metals like tungsten have very high melting points (3422 °C) due to strong metallic bonds. Non-metals like sulfur melt at 115 °C and bromine at -7 °C because they are molecular solids held together by weak van der Waals forces, requiring much less energy to melt.
Chemical Properties of Metals
Metals generally react chemically due to their tendency to lose electrons and form positive ions (cations). Their reactivity depends on factors such as metallic bonding strength, ionisation energy, and position in the Periodic Table.
Reaction with dilute acids:
Metals react with dilute acids, such as hydrochloric acid (HCl) or sulfuric acid (H₂SO₄), to produce a salt and hydrogen gas. The general reaction is:
\( \text{Metal} + \text{Acid} \rightarrow \text{Salt} + \text{H}_2 \)
Example reactions:
- \( \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \)
- \( \text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2 \)
Reaction with cold water and steam:
Some metals react with water to form a metal hydroxide and hydrogen. More reactive metals react with cold water, while less reactive metals react only with steam.
With cold water:
\( 2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2 \)
With steam:
\( \text{Fe} + \text{H}_2\text{O (g)} \rightarrow \text{FeO} + \text{H}_2 \)
Very reactive metals (Group 1) react violently with cold water, while moderately reactive metals like iron react slowly with steam at high temperature.
Example
Explain the Reaction of magnesium with dilute hydrochloric acid.
▶️Answer/Explanation
Magnesium reacts with HCl to form magnesium chloride and hydrogen gas:
\( \text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2 \)
Bubbles of hydrogen gas are observed, and the reaction is exothermic.
Example
Explain the Reaction of sodium with cold water.
▶️Answer/Explanation
Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen gas:
\( 2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2 \)
The reaction produces heat, causing the hydrogen gas to ignite sometimes. This demonstrates the high reactivity of Group 1 metals with water.