NCERT Class 7 Science Curiosity Chapter 04 The World of Metals and Non metals PDF Download

Chapter 4: The World of Metals and Non-metals

Yashwant and Anandi live in a village in Rajasthan. Their school has assigned them a project to learn about craftspersons who work with metals. They decide to visit the local ironsmiths who practise this craft. Yashwant and Anandi request their grandfather to accompany them (Fig. 4.1). They are curious to learn how these ironsmiths make different items of daily use. They interact with an elderly craftsperson, Sudarshan uncle.

Yashwant: Which items do you generally make?

Sudarshan: Generally, we make items of daily use, such as flat pans (tawas), buckets (baltis), tongs (chimtas), and farming tools like spades (phawras), axes (kulhadis), trowels (khurpis), and rakes (jelees).

Anandi: What materials are they made of?

Sudarshan: We use iron metal to make these items. We also use wood to prepare handles wherever required. Additionally, we use coal in our furnaces to heat the iron.

Sudarshan is heating an iron block in the furnace. It has become red hot. He starts beating it hard with a hammer.

Anandi is amazed and asks, "Why are you beating it?"

Sudarshan: I am beating it to shape it into an axe.

Anandi: Wow, a piece of iron can be beaten into a flat shape! Can we do this with other metals as well?

You may also have many such questions - let us explore what else we can do with metals.

[Figure 4.1: Ironsmith making various items, See in your textbook]

4.1 Properties of Materials

4.1.1 Malleability

Activity 4.1: Let us explore

Caution - Conduct this activity under the supervision of your teacher or an adult.

• Collect some waste pieces of copper and aluminium, an iron nail, a piece of coal, a pea-sized lump of sulfur (gandhak), and a block of wood.
• Recall the chapter 'Materials Around Us' in the Grade 6 Science textbook Curiosity and observe the appearances of the above items. Are they lustrous? Also, note whether they are hard or soft and record your observations in Table 4.1.
• Now, place each of these items one by one on any hard surface and beat them with a hammer (Fig. 4.2).
• What do you think will happen? Do the objects become slightly flattened or do they break into pieces?
• Record your observations in Table 4.1.

[Figure 4.2: Beating an iron nail with a hammer, See in your textbook]

Table 4.1: Appearance, hardness, and effect of hammering on different objects or materials

Analyse Table 4.1. Identify the objects that are lustrous in appearance and hard. You might have observed that objects made from copper, aluminium, and iron are lustrous in appearance and are hard. Lustre shown by metals is known as metallic lustre. Materials like copper, aluminium, and iron are known as metals, whereas, coal, sulfur, and wood are non-lustrous and not as hard as metals.

Are all metals hard and solid? Not really; some metals like sodium and potassium are so soft that they can be cut with a knife. There is one metal, mercury, that is found in a liquid state at room temperature, which you might have seen in thermometers. Recall the chapter 'Temperature and its Measurement' from the Grade 6 Science textbook Curiosity.

Teacher's Note

When you think of metals, do not assume they are all hard and shiny like iron or steel. Mercury is liquid at room temperature, and sodium is so soft you can cut it with a knife. Each metal has its own set of properties, and these properties make them useful for different jobs. Hammering is just one test for malleability - it does not tell you everything about a metal.

Which objects did you find become flat on beating with a hammer?

You must have observed that objects such as a piece of copper, an iron nail, and a piece of aluminium become flat when beaten; whereas other objects or materials behave differently. This property by which materials can be beaten into thin sheets is called malleability. Most metals possess this property. Can you give some examples of metal sheets? You might have seen thin silver foil on some sweets and aluminium foil used for wrapping food items. These are formed due to their malleability. Gold and silver are the most malleable metals.

Teacher's Note

Malleability is specifically about being beaten into sheets - do not confuse it with ductility, which is about being drawn into wires. When a hammer flattens copper or gold, that is malleability at work. In your exam, if they ask "Why can we make aluminium foil from aluminium metal?" the answer is malleability. Look for the words "beaten", "sheets", or "thin" to spot malleability questions.

Key Points

• Metals like copper, aluminium, and iron have a shiny appearance called metallic lustre and are generally hard, but not all metals are hard - some like sodium are very soft, and mercury is liquid.
• Malleability is the property of metals that allows them to be beaten into thin sheets without breaking, which is why we can make foil and metal sheets from metals like gold, silver, and aluminium.
• Non-metals like coal, sulfur, and wood are non-lustrous and when beaten they break into pieces rather than flatten.

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