Metals and Nonmetals- NCERT Notes UPSC

Physical Properties of Metals

• Conduction: Metals are good conductor of heat and electricity. Therefore, electric wires are made of metals like copper and aluminium.
• Hardness: Most of the metals are hard except alkali metals such as sodium, potassium, lithium, etc. Alkali metals are very soft metals can be cut by using a knife.
• Strength: Metals are strong and have high tensile strength except Sodium and potassium.
• State: Metals are Solid at room temperature except for mercury.
• Sound: They produce ringing sound, so also called Sonorous. Therefore, metal wires are used in making musical instruments.
• Malleability: Metals can be beaten into a thin sheet. 
• Ductility: Metals can be drawn into thin wire.
• Melting and Boiling Point: Metals generally have high melting and boiling points except sodium and potassium.
• Density: Most of the metals have a high density.
• Colour: Most of the metals are grey in colour except gold and copper.
• Lustre: Generally Shiny in appearance.

Physical Properties of Non-Metals

• Conduction: Non-metals are a bad conductor of heat and electricity except Graphite which is an allotrope of carbon.
• Hardness: They are generally soft except diamond which is the hardest naturally occurring substance.
• State: Non-metals may be solid, liquid or gas. Generally, they are brittle.
• Sound: They do not produce a typical sound on being hit and hence are non-sonorous.
• Malleability and ductility: They do not exhibit these properties.
• Melting and boiling point: Non-metals have generally low melting and boiling points.
• Density: Most of the non-metals have low density.
• Colour: Non-metals are in many colours.
• Lustre: They are Dull in appearance except diamond and iodine.

Chemical Property of Metals

• Reaction with Air:
• Metals combine with oxygen to form metal oxides. 

Metal + Oxygen → Metal oxide

• Metals react with oxygen at different rates:
  • Metals such as potassium and sodium react vigorously and catch fire in open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil. 
  • Silver and gold do not react with oxygen even at high temperatures.
  • At ordinary temperature, the surfaces of metals such as magnesium, aluminium, zinc, lead, etc. are covered with a thin layer of oxide. It prevents them from further oxidation.

• Reaction with Water: Most Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide. 

• Metals react violently with cold water. In case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire.
• Magnesium does not react with cold water, but it reacts with hot water to form magnesium hydroxide and hydrogen. It also starts floating due to the bubbles of hydrogen gas sticking to its surface.
• Metals like aluminium, iron and zinc do not react either with cold or hot water. But they react with steam to form the metal oxide and hydrogen.
• Metals such as lead, copper, silver, and gold do not react with water at all.

• Reaction with Acids:  Metals react with acids to give salt and hydrogen gas.

• Aqua regia can even dissolve gold and platinum. 

• Reaction with Solutions of other Metal Salts: 
• Reactive metals can displace less reactive metals from their compounds in solution or molten form. 

Metal A + Salt solution of B → Salt solution of A + Metal B

• If metal A displaces metal B from its solution, it is more reactive than B.

• The Reactivity Series: It is a list of metals arranged in the order of their decreasing activities. 

Relative reactivities of metals

Reaction of Metals and Non-metals

• Metals lose valence electron(s) and form cations.
• Non-metals gain those electrons in their valence shell and form anions.
• The cation and the anion are attracted to each other by strong electrostatic force, thus forming an ionic bond.

Ionic Compounds

Ionic compounds are neutral compounds made up of positively charged ions called cations and negatively charged ions called anions. For example, MgCl₂, NaCl etc.

Properties of Ionic Compounds

• Physical nature: Solid, hard, and generally brittle
• Melting and boiling points: High
• Solubility: Generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.
• Conduction of Electricity: Conduct electricity in molten state only

Occurrence of Metals

The earth’s crust is the major source of metals. Seawater also contains some soluble salts such as sodium chloride, magnesium chloride, etc.

• The elements or compounds, which occur naturally in the earth’s crust, are known as minerals.
• At some places, minerals contain a very high percentage of a particular metal and the metal can be profitably extracted from it. These minerals are called ores.

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Activity Series and Related Metallurgy

Based on reactivity, metals can be grouped into the following three categories:

• Metals of low reactivity: They lie at the bottom of the activity series and are often found in a free state. For example, gold, silver, platinum, and copper.
• Metals of medium reactivity: They lie in the middle of the activity series (Zn, Fe, Pb, etc.) and are found in the earth’s crust mainly as oxides, sulphides, or carbonates.
• Metals of high reactivity: They lie at the top of the activity series (K, Na, Ca, Mg and Al) and are never found in nature as free elements.

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Extraction of Metals

Different techniques are used for obtaining the metals based on their reactivity. Several steps are involved in the extraction of pure metal from ores as shown in Fig. 3.2.

Enrichment of Ores: It is the removal of impurities or gangue from ore through various physical and chemical processes. 

Extracting metals towards the bottom of activity series: The oxides of these metals can be reduced to metals by heating alone. For example, Mercury and Copper.

Extracting metals in the middle of activity series: Metals such as iron, zinc, etc. are usually present as sulphides or carbonates in nature. Since it is easier to obtain a metal from its oxide than its sulphides and carbonates thus the metal sulphides and carbonates are converted into metal oxides prior to reduction.

• The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.
• The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination.

Extracting metals towards the top of the activity Series: These metals are obtained by electrolytic reduction. For example, sodium, magnesium, and calcium are obtained by the electrolysis of their molten chlorides.

Refining of Metals: The extracted metal from the ore is not very pure. Refining involves removing impurities to obtain a pure metal. The most widely used method for refining is electrolytic refining.

Electrolytic Refining: Metals like copper, zinc, nickel, silver, tin, gold, etc. are refined electrolytically. 

• Apparatus setup:

• Anode: Impure metal
• Cathode: Thin strip of pure metal
• Electrolyte: Aqueous solution of metal salt
• Process: Current is passed through the electrolyte and:

• Pure metal from the anode dissolves into the electrolyte.
• An equivalent amount of pure metal from the electrolyte is deposited on the cathode.
• Soluble impurities go into the solution. 
• Insoluble impurities settle down at the bottom of anode and are known as anode mud.

Corrosion

It is the gradual deterioration of a metal by the action of moisture, air, or chemicals present in the surrounding environment. For example,

• Silver: It become black when exposed to air. This is because it reacts with sulphur in the air to form a coating of silver sulphide.
• Copper: It reacts with moist carbon dioxide in the air and slowly loses its shiny brown surface and gains a green coat. This green substance is basic copper carbonate.
• Iron: When exposed to moist air for a long time, it acquires a coating of a brown flaky substance called rust.

Prevention from Corrosion

The rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising, or making alloys.

• Coating with paints or oil or grease: On metal surfaces application of paint or oil or grease keeps out air and moisture.
• Galvanization: It is a process of coating iron with a thin layer of zinc.
• Alloying: It is a method of improving the properties of a metal. For example, Iron is mixed with nickel and chromium to obtain stainless steel which is hard and does not rust.

Interesting Points

• Pure gold, known as 24 carat gold, is very soft.

• It is not suitable for making jewellery. 
• It is alloyed with either silver or copper to make it hard.
• Generally, in India, 22 carat gold is used for making ornaments. It means that 22 parts of pure gold is alloyed with 2 parts of either copper or silver.
• The Iron pillar near the Qutub Minar in Delhi was built more than 1600 years ago and it still stand prevented from rusting. 

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