04 Metals And Non- Metals

There are 118 elements known at present and these elements are generally classified into metals and non-metals based on their properties.
Physical properties of Metals:
1. Malleability: The property of a substance due to which it can be beaten into thin sheets is called malleability. Metals are generally malleable. E.g. Gold and silver are best malleable substances.
2. Ductility: The Property of a substance by which it can be drawn into thin wires is called ductility. Metals are ductile i.e. on beating these can be drawn into thin wires. E.g. gold is more ductile as 1 gram of gold can be drawn into a thin wire of 2 km long.
3. Conduction of heat: Metals are good conductors of heat. Silver and copper are best conductors while lead and mercury are the poor conductors of heat.
4. Conduction of electricity: Metals are good conductors of electricity. E.g. silver is the best conductor of electricity.
5. Shining Surface: Metals, in their pure state, have a shining surface also called metallic lustre. E.g. gold, silver and copper are shiny metals and can be polished.
6. Hardness: Metals are generally hard with the exceptions of sodium and potassium that can be cut by knife.
7. Density: Metals have high density except sodium and potassium.
8. Melting and boiling points: Generally metals have melting and boiling points except for sodium, potassium, mercury, cesium, gallium.
9. State at room temperature: Metals are generally solid at room temperature with an exception of mercury which is liquid.
10. Sonority: Property of producing sound on striking a hard surface. Metals are sonorous i.e. they produce sound on striking.
Physical properties Non-Metals:
1. Non metals are not malleable i.e. these can not be drawn into sheets. E.g. Sulphur and phosphorus are not malleable.
2. Non metals are not ductile but are brittle ( i.e. they break easily on hammering) E.g. Sulphur and phosphorus are brittle.
3. Non metals are bad conductors of heat. E.g. Sulphur and phosphorus are bad conductors of heat.
4. Non metals are bad conductors of electricity except carbon in the form of graphite which is a good conductor of electricity.
5. Non-metals are generally non-lustrous with an exception of iodine.
6. Non metals are generally soft except diamond which is the hardest known substance.
7. Non metals have low densities i.e. they are light.
8. Non metals have low melting and boiling points except diamond (m.p = 3500 C0 )
9. Non-metals are present in all three states, solids, liquids and gaseous, at room temperature.
10. Non metals do not produce sound on striking.

Exceptions in Physical Properties of metals and non metals:
1. Graphite, a non-metal, is a good conductor of electricity.
2. Iodine is a lustrous non-metal.
3. Diamond, an allotrope of carbon, which is a non-metal is the hardest substance while sodium and potassium, being metals are soft enough to be cut by knife.
4. Mercury, which is a metal, is liquid at room temperature while rest are solids.
5. Sodium, potassium, mercury, cesium and gallium are metals with low melting and boiling points.
6. Diamond is the non-metal with high melting and boiling points.
7. Sodium, potassium and lithium are metals with low density.
Chemical properties of Metals:
1. Reaction with oxygen:
• Almost all metals combine with oxygen to form metal oxides.
Metal + Oxygen -> Metal oxide
e.g. 2Cu + O2 -> 2CuO
• Metal oxides are basic in nature. Some metal oxides, such as aluminium oxide, zinc oxide, etc., which react with both acids as well as bases to produce salts and water are known as amphoteric oxides.
e.g. Al2O3 + 6HCl -> 2AlCl3 + 3H2O
Al2O3 + 2NaOH -> 2NaAlO2 + H2O
• Most metal oxides are insoluble in water but some dissolve to form alkalis like sodium and potassium oxides.
• Metals such as potassium and sodium react so vigorously with oxygen that they catch fire if kept in the open. So to protect them they are kept immersed in kerosene oil.
e.g. Na2O (s) + H2O (l) -> 2NaOH (aq)
2. Reaction with water:
• All metals do not react with water but only those metals which are above the hydrogen in the reactivity series reacts with water or steam. Those which react form metal oxide (or metal hydroxide) and hydrogen gas.
a. When a metal reacts with water, then metal hydroxide and hydrogen gas are formed.
Metal + Water → Metal hydroxide + hydrogen gas

2K(s) + 2H2O(l) → 2KOH (aq.) + H2(g) + heat energy

b. When a metal reacts with steam, then metal oxide and hydrogen gas are formed
Metal + Steam → Metal oxide + Hydrogen gas
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
3. Reaction with Dilute Acid:
• Most metals react with dilute acids to give a metal salt and hydrogen gas. All metals however do not react with dilute acids.
Metal + Dilute acid → Salt + Hydrogen
e.g. Sodium metal reacts with dilute hydrochloric acid acid to form sodium chloride (Salt) and hydrogen.
2Na (S) + 2 HCl (aq.)  -> 2 NaCl (aq.) + H2 (g)

Similarly Magnesium metal reacts rapidly with dilute hydrochloric acid to form magnesium chloride and hydrogen gas.

2Mg (S) + 2 HCl (aq.)  -> 2 MgCl (aq.) + H2 (g)4. 4. Reaction of metals with metal salts: A more reactive metal displaces less reactive metal from their compounds in solution or molten form.
e.g. In the reaction between zinc and copper sulphate solution, zinc which is more reactive displaces the less reactive copper from the copper sulphate solution as:

CuSO4 (aq.) + Zn (s)  -> ZnSO4 (aq.) + Cu (s)

Aqua-Regia: A freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1 is known as aqua-regia. It is a highly corrosive and fuming liquid which can dissolve all metals even gold and platinum.
Reactivity of metals / Reactivity Series of Metals: The arrangement of metals in a vertical column in the order of decreasing reactivities is called reactivity series of metals. In reactivity series, the most reactive metal is placed at the top of the column while as the least reactive metal is placed at the bottom of it.
The reactivity series of metals is shown as:

 

 

Ionic Compounds And their properties:
Ionic Compounds: The compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds. E.g. Sodium chloride (NaCl), potassium chloride (KCl), Magnesium oxide MgO)
Properties of ionic compound:
1. Ionic compounds are usually crystalline solids. E.g. Sodium chloride is a crystalline solid.
2. They have high melting and boiling points. E.g. Melting and boiling points of Sodium chloride are 800 0C and 1413 0C respectively.
3. They are generally soluble in water but insoluble in solvents such as kerosene, petrol, etc.
4. Conduction of electricity:
• Conducts electricity through solution due to involvement of charged particles (ions).
• As movement of ions is not possible in solid state, due to rigid structure, do not conduct electricity.
• In molten state this movement is overcome due to heat and thus conducts electricity.

 

Occurrence of Metals: The major source of metals is Earths crust. Sea water also contains salts of metals like sodium chloride, magnesium chloride etc. The natural substances in which the metals or their compounds are found in earth are called minerals but all minerals are not used for the extraction of metals. Those minerals from which the metals can be extracted conveniently and profitably are called ores.
Obtaining (Extraction of ) Metal from an ore: Different techniques are used for obtaining the metals form an ore on the basis of their reactivity.
1. Enrichment of ore: An ore is an impure compound containing large amount of sand and rocky material. These unwanted substances present in an ore are called gangue. Before extracting the metal from an ore, it is necessary to remove these impurities by using different methods depending upon the physical or chemical properties.

2. Extraction of Metal: To extract metals from an enriched ore, all the metals are grouped into following three categories:

a. Metals of low reactivity
b. Metals of medium reactivity
c. Metals of high reactivity.

a. Metals low reactivity: These metals are generally very unreactive. Oxides of these can be reduced to metals by heating alone.
e.g. Mercury is a less reactive metal and can be extracted from its sulphide ore known as mercury II sulphide or Cinnabar ore just by heating alone as;

2HgS(s) + 3O2 (g) + Heat → 2HgO(s) + 2SO2 (g)
b. Metals of middle reactivity: These metals are present in the middle of the reactivity series and extracted by the process of calcination or Roasting.
• Calcination: The process of converting carbonate ores into metal oxides by heating strongly in absence of air is called the calcinations.
e.g. when zinc carbonate (or calamine)is strongly heated in the absence of air, zinc oxide and carbon dioxide is formed.
ZnCO3 (s) Calcination ZnO(s) + CO2 (g)
• Roasting: The process of converting sulphide ores into metal oxides by heating strongly in the presence of air is called roasting
e.g. When zinc sulphide ore is strongly heated in the presence of oxygen, then zinc oxide and sulphur dioxide is formed.

2ZnS(s) + 3O2 (g) Roasting 2ZnO(s) + 2SO2 (g)
• The metal oxides obtained from calcinations or roasting are then converted to free metal by using reducing agents like carbon , sodium, calcium or aluminium as:
ZnO (s) + C (s) Zn (s) + CO (g)

Thermite Reaction: The reduction of metal oxide by using aluminium powder as a reducing agent is known as thermite reaction.
Fe2O3(s) + 2Al(s) 2Fe(l) + Al2O3(s) + Heat
c. Metals of high Reactivity: Since these are very reactive metals and thus cannot be obtained by displacement reactions. These metals are obtained by electrolytic refining.
They are generally obtained by electrolysis of their molten chlorides or oxides. Metals are deposited at cathode (negatively charged), while chlorine or oxygen is liberated at anode (positively charged).
e.g. Sodium metal is extracted by the electrolytic reduction (electrolysis) of molten sodium chloride as:
2NaCl (l)  -> 2Na (s) + Cl2 (g)

Refining Of Metals:

The process of purifying impure metals is known as refining of metals. The most important and widely used method for purification of metals is electrolytic refining.
Electrolytic Refining:
Electrolytic refining means refining by electrolysis. To refine a metal by electrolysis, we need:
 At Anode – Impure Metal
 At Cathode – Pure Metal
 Electrolyte – Solution of the metal salt (of the metal to be refined)
• At Anode: Pure metal from anode dissolve into electrolyte.
• At Cathode: An equivalent amount of pure metal from electrolyte is deposited at cathode.
• Soluble impurities go into solution; insoluble impurities settle at the bottom of anode called as anode mud.
 Electrolytic Refining of Copper: The apparatus used for the electrolytic refining of copper is shown in figure as:

 

It consists of an electrolytic tank containing acidified copper sulphate solution as electrolyte. A thick bloc impure copper metal is made anode and thin strip of pure metal is made cathode. When electric current is passed, then impure copper from the anode dissolves and goes into copper sulphate solution and then gets deposited on cathode. Hence, pure copper metal is produced on the cathode.
Corrosion of metals: The eating up of metal by the action of gases, moisture or acids present in air is called corrosion of metals. The corrosion of iron metal is called rusting.
When an iron object is kept for some time in damp, it gets covered with red-brown flaky substance called rust. This is called rusting of iron. Rust is mainly hydrated iron (III) oxide (Fe2O3xH2O ).

Conditions necessary for Rusting of Iron: The only conditions for rusting of iron are presence of air and presence of water.

Prevention of Rusting of Iron: Some common methods of preventing corrosion of iron are as:
I. By Painting: the most common method of preventing rusting of iron to coat its surface with a paint.
II. By applying grease or oil: When grease or oil is applied to the surface of an iron object, then air and moisture cannot come in contact with it and hence rusting is prevented.
III. By Galvanization: The process of depositing a thin layer of zinc metal on iron objects is called galvanization. Galvanization also prevents rusting of iron.
IV. By Tin or Chromium plating: When a thin layer of tin and chromium is deposited on iron objects by electroplating, then the iron is prevented from rusting.
V. By Alloying: When iron is alloyed with nickel and chromium, then stainless steel is obtained which does not rust at all.