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Pure metals have highly regular atomic structures, which gives them high electrical conductivity and distinct melting points. But pure metals are not always fit for everyday jobs—pure iron rusts, and pure gold is too soft to hold a shape. By mixing a metal with other elements, we create an alloy, a homogeneous mixture designed to improve the original metal's properties.
If you are studying for the Class 10 science exams, knowing the exact compositions of common alloys and the physical reasons behind their behaviour is a key part of the curriculum.
What are common alloys and their uses?
Alloying is primarily used to increase hardness, prevent corrosion, or change the melting point of a metal. According to the NCERT Class 10 Science syllabus, here are the core alloys you need to know:
Brass is an alloy of copper and zinc. It is more malleable and stronger than pure copper, and is widely used for decorative items and musical instruments.
Bronze is an alloy of copper and tin. It is highly resistant to corrosion, making it the traditional choice for statues, medals and coins.
Solder is an alloy of lead and tin. It has a significantly lower melting point than its constituent metals.
Amalgam is any alloy in which one of the metals is mercury. For example, a dental amalgam often contains mercury mixed with silver and tin to fill cavities.
Why do alloys conduct less electricity than pure metals?
Pure copper is an excellent conductor of electricity, which is why it is used for electrical circuits. However, copper alloys like brass and bronze are poor conductors of electricity.
The reason lies in the crystal lattice. In a pure metal, atoms of the exact same size sit in a perfectly regular, repeating grid. This smooth arrangement gives the "free" electrons a clear path to flow through the material. When a different element is added to make an alloy, its atoms are almost always a different size. These mismatched atoms disrupt the regular lattice, acting like obstacles in a hallway. As electrons try to flow, they collide with these irregular atoms and scatter, which increases the material's electrical resistance.
If you find it hard to picture how atoms pack together and scatter electrons, you can explore 3D crystal structures in the Fermi Simulation Lab to see the disruption for yourself.
Why do alloys have lower melting points?
Just as the disrupted lattice scatters electrons, it also weakens the uniform interatomic bonds of the material. Because the atoms do not fit together perfectly, the overall structure is less stable. It takes less thermal energy (heat) to break these mismatched bonds and turn the solid into a liquid.
Solder takes advantage of this property. Because the mixture of lead and tin melts at a much lower temperature than either pure lead or pure tin, solder is used for welding electrical wires. The heat required to melt the solder is low enough that it will not melt or damage the delicate copper wires it connects.
To master how intermolecular forces and metallic bonds define boiling and melting points, find their lessons in the Fermi Concept Library.
What is 22 carat gold?
Pure gold, known as 24 carat gold, is extremely soft. If a jeweller tried to make a ring out of 24 carat gold, it would bend and scratch under everyday use.
To make it hard enough for ornaments, it is alloyed with a small amount of silver or copper. As detailed by NCERT, in India, 22 carat gold is the standard for jewellery. The name means that 22 parts of the alloy are pure gold, and the remaining 2 parts are either copper or silver. This slight disruption of the gold lattice makes the resulting metal significantly harder and more durable, while keeping its bright colour.
When revising for your boards, focus on the relationship between the microscopic structure (different sized atoms disrupting the lattice) and the macroscopic properties (lower conductivity, lower melting point, and increased hardness). This is the key to answering the conceptual questions on metals and non-metals.
For more on how metals behave and react, see our guides on extracting metals for Class 10 and the everyday corrosion and rancidity in Class 10 science.
