IB DP Chemistry - S2.4.3 Alloys- Study Notes - New Syllabus - 2026, 2027 & 2028
IB DP Chemistry – S2.4.3 Alloys- Study Notes – New Syllabus
IITian Academy excellent Study Notes and effective strategies will help you prepare for your IB DP Chemistry exam.
- IB DP Chemistry 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Chemistry 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
- IB DP Chemistry 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Chemistry 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
Structure 2.4.3 — Alloys: Mixtures of Metals With Enhanced Properties
Structure 2.4.3 — Alloys: Mixtures of Metals With Enhanced Properties
Alloys
Alloys are mixtures composed of a metal and one or more other elements (which can be metals or non-metals).
They are designed to have improved or specific properties compared to pure metals.
Uses of Alloys
Pure metals are often too soft, malleable, or reactive for many applications. Alloying improves properties such as:
- Strength and hardness
- Resistance to corrosion
- Durability and wear-resistance
- Electrical or thermal conductivity
- Melting point adjustment
Bonding in Alloys: Non-Directional Metallic Bonding
In both pure metals and alloys, bonding is described by the metallic bond the electrostatic attraction between a lattice of cations and a ‘sea’ of delocalised electrons. This bonding is non-directional, meaning the forces are uniform in all directions, allowing layers to slide over one another.
In alloys, atoms of different sizes are introduced into the lattice. This distorts the regular layers and reduces the ability of layers to slide, which makes the alloy harder and less malleable than the pure metal.
Structure of Alloys
- The atomic structure of an alloy is similar to that of a metal a giant lattice but with different-sized atoms disrupting the uniformity.
- This disruption increases the strength and reduces flexibility.
Key Properties of Alloys
| Property | Explanation (Compared to Pure Metals) |
|---|---|
| Hardness | Different-sized atoms prevent easy sliding of layers → increases hardness. |
| Malleability | Reduced because of distorted lattice → layers do not slide easily. |
| Corrosion resistance | Some alloying elements form protective oxide layers (e.g., Cr in stainless steel). |
| Melting point | Often lower than pure metals because the irregular structure weakens bonding in places. |
Common Examples of Alloys
Brass
- Alloy of copper and zinc
- Stronger and more corrosion-resistant than pure copper
- Used in musical instruments, coins, fittings
Bronze
- Alloy of copper and tin
- Harder than copper; resists corrosion
- Used in statues, medals, and marine fittings
Stainless Steel
- Alloy of iron with chromium and nickel
- Chromium forms a passive oxide layer that prevents rusting
- Strong, corrosion-resistant; used in cutlery, surgical tools, architecture
Example
Why is stainless steel more suitable for surgical tools than pure iron?
▶️Answer/Explanation
Stainless steel contains chromium, which forms a thin, stable oxide layer that protects against corrosion. Pure iron would rust quickly in moist environments, making it unsuitable for surgical use.
Example
Explain how adding carbon to iron improves its properties to form steel.
▶️Answer/Explanation
Pure iron is soft and malleable because layers of iron atoms slide easily over each other.
When carbon atoms are added, they fit into spaces between iron atoms and distort the lattice.
This prevents the movement of layers, increasing strength and hardness.
Thus, steel (an alloy of iron and carbon) is much stronger than pure iron.
Example
Why is solder (an alloy of tin and lead) preferred in joining electrical circuits instead of pure metals?
▶️Answer/Explanation
Solder has a low melting point, much lower than pure tin or pure lead, making it ideal for melting and flowing easily during circuit assembly.
This property arises from the irregular atomic arrangement in the alloy, which weakens metallic bonding in certain areas.
It also solidifies quickly and conducts electricity well → ideal for circuit connections.
Example
Dental amalgam is an alloy used in tooth fillings. Why is it preferred over pure mercury or silver?
▶️Answer/Explanation
Dental amalgam is an alloy of mercury with silver, tin, and copper. Pure mercury is toxic and too soft for fillings.
When alloyed, mercury forms a strong, durable, corrosion-resistant solid that sets inside the tooth cavity.
The alloy resists wear from chewing and is biocompatible, making it ideal for dental use.