Unit 9: Uses of Metals & Metalloids
Connecting the unique properties of elements to their vital roles in industry, technology, and daily life.
9.21 Uses of s-block & p-block Metals (Na, Ca, Al, Sn)
The uses of s-block and p-block metals are directly related to their chemical and physical properties.
- Sodium (Na): Due to its high reactivity, sodium metal is not used as a structural material. However, this reactivity makes it a powerful reducing agent. It is used in the extraction of more expensive metals like titanium from their chlorides ($TiCl_4 + 4Na \rightarrow Ti + 4NaCl$). Sodium vapor is used in streetlights, producing a bright, efficient yellow light.
- Calcium (Ca): Like sodium, calcium is too reactive for everyday use. Its high reactivity makes it useful as a reducing agent in metallurgy, for example, in the extraction of uranium from its ore.
- Aluminum (Al): This metal is incredibly useful due to its unique combination of properties: low density, high strength, and excellent corrosion resistance (due to its passivating oxide layer). It is used extensively in aircraft bodies, overhead power cables (it is lighter than copper), window frames, and food packaging (cans, foil).
- Tin (Sn): Tin is unreactive and non-toxic, and it forms a protective oxide layer. Its main use is as a coating on steel cans ("tin cans") to prevent the steel from rusting and contaminating food. It is also a key component of important alloys like bronze and solder.
Solved Examples:
-
Why is aluminum used for overhead power cables instead of copper, even
though copper is a slightly better conductor?
Solution: Aluminum's main advantage is its low density. It is much lighter than copper, meaning the support pylons for the cables can be built further apart and less robustly, significantly reducing construction costs. -
What property of sodium makes it useful for extracting
titanium?
Solution: Its high reactivity. Sodium is more reactive than titanium, so it can act as a strong reducing agent to displace titanium from its compound ($TiCl_4$).
9.22 Uses of d-block Metals (Fe, Cu, Au)
The d-block metals are known for their strength, hardness, and varied chemical properties, making them some of the most important industrial materials.
- Iron (Fe): Iron is the most widely used metal, primarily because it is abundant, cheap to extract, and incredibly strong when alloyed with carbon to make steel. Steel is the backbone of modern construction, used in everything from building frames, bridges, and railway lines to car bodies, ships, and machinery. Iron's magnetic properties also make it essential for manufacturing magnets and electromagnets.
- Copper (Cu): Copper's high electrical conductivity and ductility make it the primary material for electrical wiring. Its excellent thermal conductivity makes it ideal for saucepans and heat exchangers. Its unreactivity and resistance to corrosion make it suitable for water pipes and roofing. It is also a major component of brass and bronze alloys.
- Gold (Au): Gold's primary uses stem from its extreme unreactivity, malleability, and lustre. It does not tarnish or corrode, making it perfect for jewelry and decorative items. It is also an excellent electrical conductor and is used in high-end electronic connectors and circuit boards where reliability is critical. Historically and presently, it is also a major store of monetary value.
Solved Examples:
-
Why is iron alloyed to make steel instead of being used in its pure form for
construction?
Solution: Pure iron is relatively soft and not strong enough for most construction purposes. Adding small, controlled amounts of carbon and other elements to create steel dramatically increases its hardness, tensile strength, and other mechanical properties. -
Name two properties of copper that make it ideal for water
pipes.
Solution: 1. It is unreactive and does not corrode easily when in contact with water. 2. It is malleable, allowing it to be easily bent and shaped to form plumbing systems.
9.23 Alloys
An alloy is a mixture containing a metal and at least one other element (which can be a metal or a non-metal). Alloys are created to enhance the properties of the base metal, making them harder, stronger, or more resistant to corrosion. The different-sized atoms of the added elements distort the regular lattice structure of the metal, making it more difficult for the layers to slide over one another.
| Alloy | Composition | Properties & Uses |
|---|---|---|
| Steel | Iron (Fe) and Carbon (C) (plus other elements) | Very strong and hard. Used for construction, cars, tools. |
| Brass | Copper (Cu) and Zinc (Zn) | Harder than copper, corrosion-resistant, golden appearance. Used for musical instruments, taps, decorative hardware. |
| Bronze | Copper (Cu) and Tin (Sn) | Hard, strong, corrosion-resistant. Used for statues, coins, bearings, ship propellers. |
| Solder | Tin (Sn) and Lead (Pb) | Low melting point. Used for joining electrical components in circuits. |
Solved Examples:
-
Why is bronze used for ship propellers instead of pure copper?
Solution: Bronze is an alloy of copper and tin. It is significantly harder and stronger than pure copper and, crucially for marine applications, it is highly resistant to corrosion from saltwater. -
Explain on a microscopic level why alloys are generally harder than pure
metals.
Solution: In a pure metal, the atoms are all the same size and arranged in a regular lattice. In an alloy, the different-sized atoms of the other elements disrupt this regular pattern. This makes it much more difficult for the layers of atoms to slide past one another, making the material harder and less malleable.
9.24 Uses of Metalloids (Silicon, Boron)
Metalloids have properties intermediate between metals and non-metals. Their most important characteristic is that they are semiconductors.
- Silicon (Si): Silicon is the cornerstone of the modern electronics industry. In its pure form, it is a poor conductor. However, its conductivity can be precisely controlled by adding tiny amounts of impurities (a process called doping). This allows for the creation of transistors, diodes, and integrated circuits (computer chips) that control the flow of electricity. It is also the primary component of most solar panels, which convert sunlight directly into electricity.
- Boron (B): Boron is used as a dopant in the semiconductor industry. Boron fibers are extremely strong and lightweight, and are used in high-performance composite materials for aerospace applications. Boron is also used in control rods in nuclear reactors because it is very effective at absorbing neutrons.
Solved Examples:
-
What property of silicon makes it essential for computer chips?
Solution: Its property as a semiconductor. This means its ability to conduct electricity can be turned on and off or precisely controlled, which is the basis of how transistors and logic gates in a computer chip function. -
Why are metalloids not used for electrical wiring?
Solution: Metalloids are only semi-conductive. Metals like copper are far better conductors of electricity, offering much less resistance to current flow, which is essential for efficient power transmission in wires. -
What is "doping" in the context of semiconductors?
Solution: Doping is the intentional introduction of small amounts of impurities into a pure semiconductor (like silicon) to change its electrical properties, specifically its conductivity. -
Name an alloy and the metals it is made from.
Solution: Brass is an alloy made from copper and zinc.
Knowledge Check (20 Questions)
Answer: A mixture of a metal with at
least one other element to enhance its properties.
Answer: Copper and Zinc.
Answer: Its low density combined with
high strength.
Answer: Steel is an alloy that is much
harder and stronger than pure iron.
Answer: In the electronics industry as
a semiconductor for making computer chips and solar cells.
Answer: Its low melting point.
Answer: High-quality connectors in
electronic devices.
Answer: To provide a
corrosion-resistant, non-toxic layer that prevents the steel from rusting.
Answer: High electrical conductivity
and high ductility.
Answer: Copper and Tin.
Answer: They are too soft and highly
reactive with air and water.
Answer: Its magnetic property
(ferromagnetism).
Answer: It is a material whose
electrical conductivity is intermediate between a conductor and an insulator,
and can be controlled.
Answer: The differently sized atoms in
the alloy disrupt the regular lattice, making it harder for the layers of atoms
to slide past each other.
Answer: Jewelry or dental fillings.
Answer: It is sonorous (produces a good
sound), corrosion-resistant, and can be easily shaped.
Answer: As a reducing agent in the
extraction of other metals.
Answer: The base of cooking pots and
pans, or heat sinks in computers.
Answer: Tin and Lead.
Answer: Bronze is much harder and
stronger than pure copper.