Metals and Non metals Notes

Chirag Gupta

3 years ago

Spread the love

The short notes for the chapter Metals and Non-metals are as follows:

Metals and Non Metals

There are 92 well known naturally occurring minerals of which 70 are metals and rest 20 are the non-metals.

Physical Properties of Metals and Non Metals

Property	Metals	Non-Metals
Luster	They have shining surface.	They do not have shining surface except iodine.
Hardness	Generally hard except sodium, lithium & potassium .These are soft and can be cut with knife.	Generally soft except diamond (hardest natural substance)
State	Exist as solids except mercury.	Exist as solids or gases except bromine.
Malleability	Can be beaten into thin sheets. Gold & silver are the most malleable metals.	Non-malleable
Ductility	Can be drawn into thin wires.	Non-ductile
Conductor of heat & electricity	Good conductors of heat and electricity. Ag & Cu are best conductors of heat and Pb & Hg are poor conductor of heat.	Poor conductor of heat and electricity except graphite.
Density	High density & high melting point except Na & K.	Low density & melting point.
Sonorous	Produce sound on striking a hard surface.	Not sonorous
Oxides	Metallic oxides are basic in nature.	Non-metallic oxides are acidic in nature.

Reaction between Metals and Non Metals

Reactivity of an element can be explained as tendency to attain a completely filled outermost shell.

Metals have 1, 2 or 3 e- in outermost shell and thus it is easier for them to loss e- rather than to gain. They loss e- & gains positive charge & are termed as cation.

In contrast, non-metals have 4-8 e- in outermost shell & thus they gain e- to achieve their octet. They gain e- as well as negative charge & termed as anion.

Cations & anions attract each other & are held by strong electrostatic force of attraction.

The compounds formed by the transfer of electrons from metal to non-non-metal are known as ionic compounds or electrovalent compound.

Chemical Properties of Metals
Reaction with oxygen	Metal + Oxygen → Metal Oxide (basic) 2Cu + O₂ → 2CuO 4Al + 3O₂ → 2Al₂O₃ Zn & Al form amphoteric oxides i.e., they react with both acids & bases to produce salt & water Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O Al₂O₃ + 2NaoH → 2NaAlO₂ + H₂OMetal oxides are insoluble in water but some of them dissolve in water to form alkalis. Na₂O(s) + H₂O (l) → 2NaOH(aq)	Na & K are vigorous elements & are kept immersed in kerosene oil. Protective metal oxide layer prevents the metal from further oxidation such as found in Al, Zn, Pb etc. Cu doesn’t bum but hot metal coated with CuQ black colored layer. Ag & Au do not react with O₂
Reaction with Water	Metals + Water → Metal Oxides + H₂ Metal Oxides + H₂O → Metal Hydroxide 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) + E2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) + E	Na & K: react violently with cold water. Ca: reacts less violently. Mg: reacts with hot water. Al, Fe, Zn react with steam to from metal hydroxide & H₂.
Reaction with dilute Acids	Metal + Dilute Acid → Salt + H₂ Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g) Metal + HNO₃ → H₂ not evolved Reason- HNO₃ is strong oxidizing agent & oxidized H₂ to water.	Mg & Mn react with very dil. HC1 to evolve H₂ gas. The reactivity decreases in the order Mg > Al > Zn > Fe. Cu doesn’t react with dil. HCl.
Reaction with Solutions of other Metal Salts	Reactive metals can displace less reactive metals from their compounds in solution or molten state. Metals A+ Salt solution of B → salt of A+ Metal B CuS0₄(aq) + Zn(s) → ZnSO₄(aq) + Cu(s)	Reactivity Series: List of metals in order of their decreasing activities. K > Na> Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.

Occurrence of Metals

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 arc called ores.

Corrosion

Corrosion is the deterioration of materials by chemical interaction with their environment for e.g. darkening of silver articles when exposed to air, gaining of green coat on copper, rusting of iron.
Prevention: The rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys.
• Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
• Alloy is a homogeneous mixture of two or more metals, or a metal & nonmetal. For e.g. stainless steel (alloy of Fe. Ni, & Cr), amalgam (alloy of Hg), brass (alloy of Cu & Zn) etc. The electrical conductivity & melting point of an alloy is less than that of pure metals.

Enrichment of Ores

Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue. The impurities must be removed from the ore prior to the extraction of the metal.
The processes used for removing the gangue from the ore are based on the differences between physical or chemical properties of the gangue and the ore.

Extraction of Metals

Extracting Metals towards the Top of the Activity Series

These metals are highly reactive & are obtained by electrolytic reduction. For e.g. Na, Mg, & Ca are obtained by the electrolysis of their molten chlorides.
The metals are deposited at the cathode whereas chlorine is liberated at anode.
At cathode Na⁺ + e^– →Na
At anode 2Cl^– → Cl₂ + 2e^–
Similarly, aluminium is obtained by the electrolytic reduction of aluminium oxide.

Extracting Metals Low in the Activity Series

These metals are the least reactive & are often found in a free state for e.g. An, Ag. Pt & Cu are found in the free state.
However, Cu & Ag are also found in the combined state as their sulphide or oxide ores.
The oxides of these metals can be reduced to metals by heating alone. For e.g. cinnabar (HgS), ore of mercury it is heated in air to converted it in mercuric oxide (HgO) which is then reduced to mercury by further heating.
2HgS(s) + 3O₂(g) → 2HgO(s) + 2SO₂(g)
2HgO(s) → 2Hg(l) + O(g)
Another instance is reduction of Cu₂S (ore of copper) to copper by heating.
2Cu₂S + 3O₂(g) → 2Cu₂O(s) + 2SO₂(g)
2Cu₂O + Cu₂S → 6Cu(s) + SO₂

Extracting Metals Middle in the Activity Series

These metals such as Fe, Zn, Pb, Cu, etc are moderately reactive & are usually present as sulphides or carbonates in nature.
The sulphide ores are converted into oxides by heating strongly in the presence of excess air which is known as roasting.
The carbonate ores are changed into oxides by heating strongly in limited air which is known as calcination.
The metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon.
For e.g. extraction of Zn
Roasting: 2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g)
Calcination: ZnCO₃(s) → ZnO(s) + CO₂(g)
Reduction: ZnO(s) + C(s) → Zn(s) + CO(g)
Sometimes displacement reactions can also be used in place of reduction & highly reactive metals such as Na, Ca, Al, etc., are used as reducing agents.
For e.g. 3MnO₂(s) + 4Al(s) → 3Mn(l) + 2Al₂O₃(s) + Heat
Fe₂O₃(s) + 2Al(s) → 2Fe(l)+Al₂O₃(s) + Heat
This reaction is used to join railway tracks or cracked machine parts and is known as the thermit reaction.