Elements can be broadly divided into two categories: metals and non-metals. They differ both in physical and chemical properties.
Malleability and Ductilily
Metals are malleable. They can be beaten into thin sheets. They are also ductile and can be drawn into wire. Non-metals are neither malleable nor ductile. For e.g. coal, (carbon) and sulphur.
All the metals show metallic lusture. They do not show any metallic lusture.
Metals are generally hard. Non-metals are soft in comparison to metals.
Metals exist in solid and liquid states. Non-metals exist in solid, liquid and gaseous states.
Metals are sonorous and produce characteristic metallic sound when struck. Non-metals are non sonorous.
Metals have high density. Non-metals have low density.
Metals are good conductor of electricity. Non-metals are bad conductor of electricity.
Points to Note
- Mercury is the only metal and bromine is the only non-metal which exist in liquid state at room temperature.
- Graphite and iodine possess metallic lusture though they are non-metals.
- Sodium metal is soft like wax and it can be cut with a knife.
- Gallium metal would melt if kept on our palm.
- Gold and silver are the most malleable and ductile metals.
- Diamond is a better conductor of heat than copper but poor conductor of electricity.
- Graphite is the only non-metal which is a good conductor of electricity but poor conductor of heat.
- Gold, silver, platinum and copper are found in the free state. This is because of their poor reactivity as compared to other metals.
Metals are electropositive in nature. They generally have 1, 2 or 3 electrons in their valence shells and readily lose these electrons to form positively charged ions. (cations). These cations are stable as they acquire noble gas configuration after losing the valence shell electrons.
Na(g) → Na+(gas) + e–
During electrolysis of their aqueous solutions they are discharged at the cathode. On the other hand non-metals are electronegative in nature. They generally have 5,6 or 7 electrons in their valence shells.They have tendency to form anion by gaining electrons.
Cl(g) + e– → Cl–(g)
Chemical Properties of Metals
Reaction with Oxygen
On burning, metals react with oxygen to produce metal oxides which are basic in nature. The reaction may take place without heating as in sodium, calcium or potassium, while some metals react with oxygen on heating to form oxides.
4Na(s) + O2(g) → 2Na2O(s)
Mg(s) + O2(g) → 2MgO(s)
4Al(s) + 3O2(g) → 2Al2O3(s)
Oxides of metals are basic in nature as they react with water and form bases.
Na2O(s) + H2O(l) → 2NaOH(aq)
CaO(s) + H2O(l) → Ca(OH)2(aq)
Oxides of aluminium (Al2O3), zinc (ZnO), tin (SnO) and iron (Fe2O3) are amphoteric in nature as they react with acids as well as with bases.
Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l)
Al2O3(s) + 2NaOH(aq) → 2NaAlO2(aq) + H2O(l)
Reaction with Water
Some metals react with water to produce metal hydroxides and hydrogen gas. Hydroxides are basic in nature. Sodium and potassium react with cold water.
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
Magnesium reacts with hot water.
Mg(s) + H2O(l) → Mg(OH)2(aq) + H2(g)
Metals like Al or Fe react on heating with water or with steam. In these conditions metals form metal oxides.
2Al(s) + 3H2O(g) → Al2O3(s) + 3H2(g)
Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
Reaction with Acids
Metals react with acids like dilute HCl & dilute H2SO4 and produce metal salts and hydrogen gas.
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)
Reaction with Bases
Some metals like aluminum and zinc react with common bases.
Sn(s) + 2NaOH(aq) + H2O(l) → Na2SnO3 (sodium stannate)
Zn(s) + 2NaOH(aq) → Na2ZnO2 (Sodium zincate)
Metals react with air and form their oxides. This oxide formation tendency of metals affects their physical and chemical properties. The processes of oxidation of metals are known as Corrosion. Corrosion leads to the destruction of metal surface by the action of air and moisture.
Generally the corrosion word is used for oxidation of different metals but in case of corrosion of iron, it is called rusting. When iron reacts with oxygen it produce brown powder called rust which is chemically hydrated ferric oxide.
4Fe(s) + xH2O + 3O2 → 2Fe2O3.xH2O (Brown Rust)
Methods of Prevention of Corrosion
Some of the important methods of prevention of corrosion are:
- Painting: This is a common method of preventing iron from rusting. Painting prevents rusting by providing a coating over iron objects.
- Oiling and greasing: To put a layer of oil and grease on the iron objects also prevents them from rusting. Iron parts of various machines and vehicles are oiled and greased to prevent rusting and to minimize friction.
- Galvanization: In this method we put a layer of zinc metal on the iron objects and this process is known as galvanization. This method is used on large scale for making galvanized iron sheets for making boxes and for roof covering.
- Alloying: In this method a particular metal with other metal or non-metal is mixed in a fixed proportion to improve its quality like resistance towards corrosion, strength, hardness, shining and high tensile strength. For example iron metal can not be used for making utensils because it will rust but when it is mixed with nickel and chromium metal it becomes stainless steel.
Activity Series of Metals
More reactive metals displace less reactive metals from their compounds in aqueous solutions. For example, when Fe is placed in a solution of CuSO4 it replaces Cu from the solution.
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
On the other hand if you place a silver wire in a solution of CuSO4, no reaction occurs because silver is less reactive than copper.
Ag(s) + CuSO4(aq) → No reaction
However, when a copper wire is dipped in AgNO3 solution, silver is replaced and deposited on copper wire.
Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq)
This indicates that copper is more reactive than silver. In general, a more reactive metal displaces a less reactive metal from its salt solution.
The arrangement of metals in the decreasing order of their activity is known as activity or reactivity series. It is also known as electrochemical series.
Most reactive metal to Least reactive metal:
Source of Metals
The constituents of earth crust which contain these metals or their compounds are known as minerals. At some places minerals contain a high percentage of a particular metals and the metal can be profitably extracted from it, such minerals are called ores. An ore taken out from the earth contains a lot of impurities in form of sand and other undesirable materials.
Getting pure compound of a metal from its ore and finally getting the metal from it pure compound is called metallurgy.
Metals in the lower part of the activity series are very unreactive. For example, mercury which is obtained as HgS (cinnabar) can be extracted easily.
2HgS + 3O2(g) + heat → 2HgO(s) + 2SO2(g)
On further heating, HgO is decomposed in mercury and oxygen.
2HgO(s) + heat → 2Hg(l) + O2(g)
Metals in the bottom of activity series like Ag, Au, etc are least reactive and are found in native state.
The metals in the middle of the activity series such as iron, zinc lead, etc. are moderately reactive. They are present usually as sulphide or carbonate in nature. Prior to reduction these ores are converted into oxides as it is easy to reduce metal oxides.
Roasting: 2ZnS(s) + 3O2(g) + heat → 2ZnO(g) + 2SO2(g)
Calcination: ZnCO3(s) + heat → ZnO(s) + CO2(g)
Metal oxides are reduced to corresponding metal using carbon.
ZnO(s) + C(s) → Zn(s) + CO(g)
Metal at the top of activity series are highly reactive. These metals have high affinity for oxygen and therefore can not be obtained by reduction with carbon. These metals (such as Na, K, Mg) are obtained by the process of electrolysis of their molten salt.
Chemical Reactions of Non-Metals
Non-metals react with oxygen on heating or burning to form their oxides.
S(s) +O2(g) → SO2(g)
C(s) +O2(g) → CO2(g)
2H2(g) +O2(g) → 2H2O(l)
Many non-metals form more than one oxide. Carbon with limited supply of oxygen on burning forms CO which is a neutral oxide. However in ample supply of air carbon forms CO2 which is an acidic oxide.
2C(g) + O2(g) → 2CO
C(g) + O2(g) → CO2
In general, oxides of non-metals are acidic in nature or after dissolving in water they form acids.
Carbon dioxide forms carbonic acid with water.
CO2(g) + H2O(l) → H2CO3(aq) (carbonic acid)
Sulphur trioxide forms sulphuric acid with water.
SO3(g) + H2O(l) → H2SO4(l) (Sulphuric acid)
Dinitrogen pentoxide forms nitric acid with water.
N2O5(g) + H2O(l) → 2HNO3(l) (nitric acid)
Uses of Metals
- Many metals like iron, copper and aluminium are used to make containers.
- Metals like copper, aluminium, iron and stainless steel are used to make utensils and fry pans.
- Ductile metals like copper and aluminium are used for making electrical wires. Steel ropes are used in cranes to lift heavy objects in making bridges.
- Iron and steel are used to make machines.
- Zinc, lead, mercury, lithium are used to make cells and batteries.
- Malleable metals like iron and aluminium are used to make sheets which are used for various construction purposes.
- Gold, silver and platinum metals are used to make jewellery due to their luster, high malleability and inert nature.
- Alloys of different metals and non-metals are used for various purposes. e.g. Stainless steel for making utensils
Uses of Non-Metals
- Hydrogen is used in manufacturing of ammonia gas which is further used in the manufacturing of urea (fertilizer).
- Hydrogen is a constituent of many industrial fuels like water gas (CO +H2) and coal gas (H2 + CH4).
- Silicon is used in making transistors, chips for computers and photovoltaic cells.
- Silicon is used in steel industry to deoxidize steel and it produces high quality corrosion resistant steel.
- Most of the phosphorous is used for making phosphoric acid H3PO4 which is used in the manufacturing of phosphate fertilizers.
- White phosphorous as (P4S3) is used in the match industry.
- Phosphates are added to the detergents as they help in the removal of dirt from soiled cloths.
- Sulphur is used in agriculture to control fungus and pests.
- Sulphur is used in the manufacturing of gun powder which is an intimate mixture of sulphur, charcoal and potassium nitrate.
- Most of sulphur is converted into sulphuric acid which is called the king of chemicals and is used to make variety of other chemicals.