IB Chemistry S2.4.3 Alloys Notes

Alloys: Enhanced Materials Through Metallic Bonding

1. Unlike compounds, where elements are chemically bonded in fixed ratios, alloys are mixtures of a metal with one or more other elements.
2. They are typically created by melting the components together and allowing the mixture to solidify.
3. The resulting material often has properties that are superior to those of the pure metal.

Key Features of Alloys:

1. Improved strength: Alloys are often harder and stronger than their pure metal counterparts.
2. Corrosion resistance: Many alloys resist rust and oxidation better than pure metals.
3. Tailored properties: By adjusting the composition, alloys can be designed for specific applications, such as electrical conductivity, heat resistance, or malleability.

Metallic Bonding and Alloy Properties

To understand why alloys have such remarkable properties, we need to revisit the concept of metallic bonding.

1. In pure metals, atoms are arranged in a regular lattice.
2. Outer electrons are delocalized and can move through the structure.
3. This explains typical metal properties such as electrical conductivity and malleability.

Non-Directional Bonding in Metals

1. Metallic bonds are non-directional, meaning the attraction between the positive metal ions and the delocalized electrons is uniform in all directions.
2. Because the bonding is non-directional, layers of metal ions can slide while remaining attracted to the same sea of electrons.
3. This explains why many pure metals are malleable and ductile.

Why Alloys Are Stronger

1. In a pure metal, equal-sized atoms form regular layers that slide relatively easily.
2. In an alloy, atoms of different sizes distort the lattice and hinder the movement of layers.
3. More force is needed for the layers to slide, so the alloy is harder and stronger and usually less ductile.

Examples of Common Alloys

Bronze

1. Composition: Copper and tin.
2. Properties: Harder and more corrosion-resistant than pure copper.
3. Uses: Statues, coins, and tools.

Stainless Steel

1. Composition: Iron, chromium, and often nickel.
2. Properties: Highly resistant to corrosion, strong, and shiny.
3. Uses: Cutlery, surgical instruments, and construction materials.

Brass

1. Composition: Copper and zinc.
2. Properties: Malleable, corrosion-resistant, and has a golden appearance.
3. Uses: Musical instruments, decorative items, and plumbing fixtures.