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CBSE NOTES CLASS 10 SCIENCE CHAPTER 3

METALS AND NON-METALS

Physical properties of metals and non metals

Ductility

Malleability

Sonority

Exceptions in properties of metals and non-metals

Chemical properties of metals

Reaction of metals with oxygen (burning)

Behaviour of Metal Oxides

Anodising

Reactions of Metals with Water

Reactions of Metals with Compounds of Other Metals

The Reactivity Series

Reaction of Metals with Non-metals

Ionic Compounds

General properties of ionic compounds

Occurrence of Metals

Minerals

Ores

Gangue

Extraction of Metals

Extracting Metals Low in the Activity Series

Extracting Metals in the Middle of the Activity Series

Roasting

Calcination

Thermite Reaction

Extracting Metals towards the Top of the Activity Series

Refining of Metals

Electrolytic Refining

Corrosion

Methods of protecting the metals from corrosion

CBSE NOTES CLASS 10 SCIENCE CHAPTER 3

METALS AND NON-METALS

Physical Properties of Metals and Non Metals

Property

Metals

Non Metals

Lustre (shine)

Lustrous (shiny)

Have no luster, except Iodine.

Colour

Usually grey or white

All colours

State of matter at room temperature

Usually solid (exception is mercury)

Exist as solid, liquid or gas.

Hardness

Metals are generally hard. Exception Na, K

Not as hard as metals. Exception diamond.

Melting Point and Boling Point

Have high MP and BP. Exception Gallium and Caesium.

Low melting and boiling points. Exception diamond.

Ductility

Ductile

Not ductile

Malleability

Malleable

Not malleable

Conductivity

Good conductors of heat and electricity. Lead and mercury are poor conductors.

Bad conductors of heat and electricity. Exception graphite.

Sonority

Sonorous

Not sonorous

Ductility

Property of metals by virtue of which they can be drawn into thin wires is called ductility.

Malleability

Property of metals by virtue of which they can be beaten into thin sheet is called malleability.

Sonority

Property of metals, by virtue of which they make a bell-like sound when struck.

Exceptions

(i) All metals except mercury exist as solids at room temperature.

(ii) Usually metals have high melting points but gallium and caesium have very low melting points. These two metals will melt if you keep them on your palm.

(iii) Iodine and carbon (graphite) are a non-metal but they are lustrous.

(iv) Carbon is a non-metal that can exist in different forms called allotropes. Diamond, an allotrope of carbon, is the hardest natural substance known and has a very high melting and boiling point. Graphite, another allotrope of carbon, is a conductor of electricity.

(v) Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. They have low densities and low melting points.

(vi) Bromine is the only liquid non metal.

CHEMICAL PROPERTIES OF METALS

Reaction of Metals with Oxygen (Burning)

Almost all metals combine with oxygen to form metal oxides.

Depending on the reactivity of the metal, they react differently with oxygen.

Behaviour of Metal Oxides

Anodising

Anodising is a process of forming a thick oxide layer of aluminium. Aluminium develops a thin oxide layer when exposed to air. This aluminium oxide coat makes it resistant to further corrosion. The resistance can be improved further by making the oxide layer thicker. During anodising, a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer. This oxide layer can be dyed to give aluminium articles with an attractive finish.

Reactions of Metals with Water

Reactions of Metals with Acids

Metals react with acids to give a salt and hydrogen gas.

Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because HNO3 is a strong oxidising agent. It oxidises the H2 produced to give water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2). But magnesium (Mg) and manganese (Mn) react with very dilute HNO3 to evolve H2 gas.

The reactivity decreases in the order Mg > Al > Zn > Fe.

This shows that copper does not react with dilute HCl.

Aqua regia (Latin for ‘royal water’):

Aqua regia is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that are able to dissolve gold and platinum. It can dissolve gold, even though neither of these acids can do so alone.

Reactions of Metals with Compounds of Other Metals

Reactive metals can displace less reactive metals from their compounds in solution or molten form.

The Reactivity Series

Reaction of Metals with Non-metals

Elements take part in chemical reaction to attain a completely filled valence shell or a noble gas configuration.

Atoms of metals loose electron to attain the stable octet and give positively charged ions (cation).

Similarly atoms of non-metals gain electron to attain the stable octet and give negatively charged ions (anion).

Also,

General properties of ionic compounds

(i) Physical nature: Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive and negative ions. These compounds are generally brittle and break into pieces when pressure is applied.

(ii) Melting and Boiling points: Ionic compounds have high melting and boiling points. This is because a considerable amount of energy is required to break the strong inter-ionic attraction.

(iii) Solubility: Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.

(iv) Conduction of Electricity: The conduction of electricity through a solution involves the movement of charged particles. A solution of an ionic compound in water contains ions, which move to the opposite electrodes when electricity is passed through the solution. Ionic compounds in the solid state do not conduct electricity because movement of ions in the solid is not possible due to their rigid structure. But ionic compounds conduct electricity in the molten state. This is possible in the molten state since the elecrostatic forces of attraction between the oppositely charged ions are overcome due to the heat. Thus, the ions move freely and conduct electricity.

Occurrence of Metals

Minerals

The elements or compounds, which occur naturally in the earth’s crust, are known as minerals.

Ores

Minerals which contain a very high percentage of a particular metal and the metal can be profitably extracted from them, are called ores.

Gangue

The impurities, like sand, in an ore are called gangue.

Different techniques used for removing the gangue from the ore are based on the differences between the physical or chemical properties of the gangue and the ore.

The process of removal of gangue from the ore is called concentration of ore.

EXTRACTION OF METALS

On the basis of reactivity, we can group the metals into the following three categories

(i) Metals of low reactivity;

(ii) Metals of medium reactivity;

(iii) Metals of high reactivity.

Different techniques are to be used for obtaining the metals falling in each category.

PotassiumSodiumCalciumAluminiumMagnesium

Electrolysis

ZincIronLead 

Reduction with C

CopperMercury

Roasting

SilverGold

Free state

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Extracting Metals Low in the Activity Series

The oxides of these metals can be reduced to metals by heating. For example, cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO) and then to mercury on further heating.

2HgS(s) + 3O2 (g)       heat       2HgO(s) + 2SO2 (g) 

Similarly, copper which is found as Cu2S in nature can be obtained from its ore by just heating in air.

Extracting Metals in the Middle of the Activity Series

Extracting Metals towards the Top of the Activity Series

Refining of Metals

Corrosion

It is the process in which metals are slowly eaten up by the action of air, moisture or chemicals.

Methods of protecting the metals from corrosion