Metals and Non-metals

Malleable: Substances that can be beaten into thin sheets are called malleable. For example, most of the metals are malleable. Ductile: Substances that can be drawn into thin wires are called ductile. For example, most of the metals are ductile.

Sodium and potassium are very reactive metals and and combine explosively with air as well as water. Hence, they catch fire if kept in open. Therefore, to prevent accidental fires and accidents, sodium is stored immersed in kerosene oil.

(i) When iron reacts with steam, it forms iron(II,III) oxide (magnetic oxide) and hydrogen gas:

(ii) Calcium reacts vigorously with cold water:

Potassium reacts very violently with cold water, often catching fire:

Explanation A + FeSO4 → No reaction, i.e., A is less reactive than iron A + CuSO4 → Displacement, i.e., A is more reactive than copper B + FeSO4 → Displacement, i.e., B is more reactive than iron B + ZnSO4 → No reaction, i.e., B is less reactive than zinc C + FeSO4 → No reaction, i.e., C is less reactive than iron C + CuSO4 → No reaction, i.e., C is less reactive than copper C + ZnSO4 → No reaction, i.e., C is less reactive than zinc C + AgNO3 → Displacement, i.e., C is more reactive than silver D + FeSO4/CuSO4/ZnSO4/AgNO3 → No reaction, i.e., D is less reactive than iron, copper, zinc, and silver From the above equations, we obtain: (i) B is the most reactive metal. (ii) If B is added to a solution of copper (II) sulphate, then it would displace copper. B + CuSO4 → Displacement (iii) The arrangement of the metals in the order of decreasing reactivity is: B > A > C > D

Hydrogen gas is evolved when dilute hydrochloric acid is added to a reactive metal. When iron reacts with dilute H2SO4, iron (II) sulphate with the evolution of hydrogen gas is formed.

Zinc is more reactive than iron. Therefore, if zinc is added to a solution of iron(II) sulphate, zinc will displace iron from the solution. The colour of iron sulphate (light green) will fade and the iron gets deposited at the bottom.

(i) The electron-dot structures (Lewis structures) for the elements:

• Sodium (Na): Sodium has 1 valence electron represented as Na with one dot.

• Oxygen (O): Oxygen has 6 valence electrons represented as O with six dots.

• Magnesium (Mg): Magnesium has 2 valence electrons represented as Mg with two dots.

(ii) Formation of Na₂O: Each sodium atom loses 1 electron to oxygen. Oxygen (which needs 2 electrons) accepts one electron from each of the two sodium atoms to complete its octet.

Formation of MgO: Magnesium loses 2 electrons to oxygen, which accepts 2 electrons to complete its octet.

(iii) The ions present in Na₂O are Na⁺ and O²⁻ ions. The ions present in MgO are Mg²⁺ and O²⁻ ions.

Ionic compounds have strong electrostatic forces of attraction between the ions. Therefore, it requires a lot of energy to overcome these forces. That is why ionic compounds have high melting points.

(i) Mineral: Most of the elements occur in nature as in combined state as minerals. The chemical composition of minerals is fixed. (ii) Ore: Minerals from which metals can be extracted profitably are known as ores. (iii) Gangue: The impurities (sand, silt, soil, gravel, etc.) present in the ore are called gangue.

The metals at the bottom of the reactivity series are mostly found in free state. For example: gold, silver, and platinum.

The chemical process used for obtaining a metal from its oxide is reduction. In this process, metal oxides are reduced by using suitable reducing agents such as carbon or by highly reactive metals to displace the metals from their oxides.

For example:

Oxides of more reactive metals are reduced by electrolysis.

Metal Zinc Magnesium Copper Zinc oxide No reaction DisplacementNo reaction Magnesium oxide No reaction No reaction No reaction Copper oxide DisplacementDisplacementNo reaction

More reactive a metal is, more likely it is to be corroded. Therefore, less reactive metals are less likely to get corroded. This is why gold plating provides high resistance to corrosion.

Alloys are homogeneous mixtures of two or more elements. The elements could be two metals, or a metal and a non-metal. An alloy is formed by first melting the metal and then dissolving the other elements in it. For example, steel is an alloy of iron and carbon.

(d) AgNO3 solution and copper metal

(c) Applying a coating of zinc (We can also apply grease and paint to prevent iron from rusting. However, in case of iron frying pan, grease and paint cannot be applied because when the pan will be heated and washed again and again, the coating of grease and paint would get destroyed.)

(a) The element is likely to be calcium

(c) Food cans are coated with tin and not with zinc because zinc is more reactive than tin.

(a) With the hammer, we can beat the sample and if it can be beaten into thin sheets (that is, it is malleable), then it is a metal otherwise a non-metal. Similarly, we can use the battery, bulb, wires, and a switch to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal. (b) The above tests are useful in distinguishing between metals and non-metals as these are based on the physical properties. No chemical reactions are involved in these tests.

Give two examples of amphoteric oxides. Those oxides that behave as both acidic and basic oxides are called amphoteric oxides. Examples: aluminium oxide (Al2O3), zinc oxide (ZnO)

Metals that are more reactive than hydrogen displace it from dilute acids. For example: sodium and potassium. Metals that are less reactive than hydrogen do not displace it. For example: copper and silver.

In the electrolytic refining of a metal M: Anode → Impure metal M Cathode → Thin strip of pure metal M Electrolyte → Solution of salt of the metal M

(a) When sulphur is heated, it burns in oxygen to form sulphur dioxide (SO₂) gas:

(i) There will be no action on dry litmus paper because SO₂ needs moisture to form an acid.

(ii) SO₂ reacts with moisture to form sulphurous acid, which turns moist blue litmus paper to red:

(b) The balanced chemical equation for the reaction:

Two ways to prevent the rusting of iron are: (i) Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented. (ii) Galvanisation: An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.

Non-metals combine with oxygen to form acidic oxides. For example:

These oxides react with water to form acids. For example, SO₂ reacts with water to form sulphurous acid.

(a) Platinum, gold, and silver are used to make jewellery because they are very lustrous. Also, they are very less reactive and do not corrode easily. (b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water. Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture. (c) Though aluminium is a highly reactive metal, it is resistant to corrosion. This is because aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils. (d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides

Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.

Metal Non- metal Metals are electropositive. Non-metals are electronegative. They react with oxygen to form basic oxides. They react with oxygen to form acidic or neutral oxides. These have ionic bonds. These have covalent bonds. They react with water to form oxides and hydroxides. Some They do not react with water. metals react with cold water, some with hot water, and some with steam. They react with dilute acids to form a salt and evolve They do not react with dilute hydrogen gas. However, Cu, Ag, Au, Pt, Hg do not react. acids. These are not capable of replacing hydrogen. They react with the salt solution of metals. Depending on These react with the salt solution their reactivity, displacement reaction can occur. of non-metals. They act as reducing agents (as they can easily lose These act as oxidising agents (as electrons). they can gain electrons).

He must have dipped the gold metal in the solution of aqua regia − a 3:1 mixture of conc. HCl and conc. HNO3. Aqua regia is a fuming, highly corrosive liquid. It dissolves gold in it. After dipping the gold ornaments in aqua regia, the outer layer of gold gets dissolved and the inner shiny layer appears. That is why the weight of gold ornament reduced.

Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water. That is why copper is used to make hot water tanks, and not steel.