NCERT Class 7 Science Chapter 4
The World of Metals and Non-metals
This chapter explores the physical and chemical properties of metals and non-metals for CBSE Class 7 students. Students learn to distinguish metals from non-metals based on properties like lustre, conductivity, malleability, and ductility, and study how metals react with air, water, and acids. The chapter also covers the uses of common metals and non-metals in daily life.
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Key Terms
- Metal
- A substance that is typically shiny (lustrous), hard, a good conductor of heat and electricity, malleable, and ductile. Examples include iron, copper, and aluminium.
- Non-metal
- A substance that is generally dull, brittle, and a poor conductor of heat and electricity. Examples include carbon, sulphur, and oxygen.
- Malleability
- The property of metals that allows them to be beaten into thin sheets without breaking. Gold and silver are highly malleable.
- Ductility
- The property of metals that allows them to be drawn into thin wires. Copper is widely used for electrical wires due to its high ductility.
- Lustre
- The shiny appearance of metals due to their ability to reflect light from their surface.
- Corrosion
- The gradual deterioration of metals due to chemical reactions with substances in the environment, such as rust forming on iron when exposed to air and moisture.
Frequently Asked Questions
What are the properties of metals in Class 7 Science?▾
Metals are lustrous (shiny), hard, malleable (can be beaten into sheets), ductile (can be drawn into wires), and good conductors of heat and electricity. Most metals are solid at room temperature, except mercury which is liquid.
How are non-metals different from metals?▾
Non-metals are generally dull, brittle, and poor conductors of heat and electricity. Unlike metals, non-metals cannot be beaten into sheets or drawn into wires. Examples of non-metals include carbon, sulphur, and phosphorus.
What is corrosion and how can it be prevented?▾
Corrosion is the chemical process by which metals are gradually destroyed when they react with substances like oxygen and moisture. Rusting of iron is a common example. It can be prevented by painting, oiling, galvanising, or coating the metal with another material.
Why is copper used for making electrical wires?▾
Copper is used for electrical wires because it is highly ductile (can be drawn into thin wires), an excellent conductor of electricity, and relatively affordable compared to other good conductors like silver.
What are the uses of non-metals in everyday life?▾
Non-metals have many important uses. Oxygen is essential for breathing and burning. Carbon in the form of graphite is used in pencils. Nitrogen is used in fertilisers. Sulphur is used in medicines and matchsticks.
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