Maharashtra Board Class 10 Science Part 1 Chapter 8 Metallurgy PDF Download

Metallurgy

Earth was born about 4.5 billion years ago. Various formative processes have been taking place in the core of the earth and its surroundings since its creation till today. These have resulted in the formation of various ores, liquids and gases.

The substances around us are in the form of some or the other elements or their compounds. In the beginning, elements were classified in accordance with their chemical and physical properties into the types metals, nonmetals and metalloids, and these are in use even today. You have studied their characteristics in the last standard. We are going to get more information about them in this lesson.

What are the physical properties of metals and nonmetals?

Physical Properties Of Metals

Metals exist mainly in solid state. The metals namely, mercury and gallium exist in liquid state at room temperature. Metals possess luster. The metallic luster goes on decreasing due to exposure to atmospheric oxygen and moisture and also in presence of some reactive gases.

We know that metals have the properties namely, ductility and malleability. Similarly, all metals are good conductors of heat and electricity. Generally, all metals are hard. However, the alkali metals from group 1 such as lithium, sodium and potassium are exceptions. These metals can be cut with knife as they are very soft. Metals have high melting and boiling points. For example, tungsten metal has the highest melting point (3422 °C). On the contrary, the melting and boiling points of the metals such as sodium, potassium, mercury, gallium are very low. A sound is produced when certain metals are struck. This is called sonority. These metals are known as sonorous metals.

Teacher's Note

Metals are hard and shiny things. But sodium is soft like butter and can be cut with a knife. Just like how your school bell makes a sound, some metals also make sound when we hit them.

Exam Trick

Remember: Mercury and gallium are liquid metals. Think of mercury in thermometers - it is liquid metal! All other metals are solid.

Points to Remember

Metals are shiny and hard.
Most metals conduct heat and electricity well.
Metals can be bent and stretched (ductility and malleability).
Some metals like sodium are soft and can be cut with a knife.
Metals make sound when hit - this is called sonority.

Physical Properties Of Nonmetals

When properties of nonmetals are considered, it is found that some nonmetals are in solid state while some are in gaseous state. Exception is the nonmetal bromine which exists in liquid state. Nonmetals do not possess luster, but iodine is the exception as its crystals are shiny. Nonmetals are not hard. Diamond which as an allotrope of carbon is the exception. Diamond is the hardest natural substance. Nonmetals have low melting and boiling points. Nonmetals are bad conductors of electricity and heat. Graphite, an allotrope of carbon, is an exception, as it is a good conductor of electricity.

Substances which are good conductors of heat are usually good conductors of electricity as well. Similarly bad conductors of heat are also bad conductors of electricity. The exception is diamond which is bad conductor of electricity but good conductor of heat.

Teacher's Note

Nonmetals are not shiny and not hard. Carbon in your pencil is a nonmetal. Oxygen in the air we breathe is also a nonmetal. Nonmetals are poor conductors of heat and electricity.

Exam Trick

Remember: Diamond is the hardest thing but it does NOT conduct electricity. Graphite is soft but it DOES conduct electricity. Both are made of carbon but are different!

Points to Remember

Nonmetals are not shiny.
Nonmetals are not good conductors of heat and electricity.
Nonmetals are usually not hard.
Diamond is an exception - it is very hard.
Graphite is an exception - it conducts electricity.

Chemical Properties Of Metals

Metals are reactive. They lose electrons easily and become positively charged ions. That is why metals are called electropositive elements.

The apparatus needed: Pair of tongs or spatula, knife, burner, etc.

The chemicals needed: Samples of aluminium, copper, iron, lead, magnesium, zinc and sodium. (Note: Use sodium carefully, in presence of teacher)

Procedure: Hold the sample of each of the above metals at the top of the flame of a burner with the help of a pair of tongs, or a spatula.

Questions to answer:

1. Which metal catches fire readily?

2. How does the surface of a metal appear on catching fire?

3. What is the colour of the flame while the metal is burning on the flame?

Reactions Of Metals

a. Reaction Of Metals With Oxygen

Metals combine with oxygen on heating in air and metal oxides are formed. Sodium and potassium are very reactive metals. Sodium metal combines with oxygen in the air even at room temperature and forms sodium oxide.

\[4\text{Na(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{Na}_2\text{O(s)}\]

On exposure to air sodium readily catches fire. Therefore, to prevent accident in the laboratory or elsewhere it is kept in kerosene. Oxides of some metals are soluble in water. They react with water to form alkali.

\[\text{Na}_2\text{O (s)} + \text{H}_2\text{O (l)} \rightarrow 2\text{NaOH (aq)}\]

We know that magnesium oxide is formed on burning magnesium ribbon in the air. Magnesium oxide reacts with water to form an alkali, called magnesium hydroxide.

\[2\text{Mg(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{MgO(s)}\] \[\text{MgO} + \text{H}_2\text{O} \rightarrow \text{Mg(OH)}_2\]

Teacher's Note

When you heat sodium in air, it catches fire very quickly. That is why sodium is kept in kerosene oil in the laboratory so it does not touch air. This is like how we keep important things safe in boxes.

Exam Trick

Remember: Reactive metals like sodium catch fire in air. That is why it is stored in kerosene. Think of it like this - Keep sodium away from air, just like you keep water away from fire!

Points to Remember

Metals react with oxygen when heated.
Sodium and potassium catch fire very easily.
Metal oxides are formed when metals burn.
Some metal oxides dissolve in water to form alkali.
Sodium is stored in kerosene to keep it safe from air.

This is a preview of the first 3 pages. To get the complete book, click below.