In this chapter we discuss about various elements such as Metal and Non-metals and how elements can be classified as metals or non-metals on the basis of their properties. we uses uses of metals and non-metals in our daily life, but we donot know what is the difference them. Lets find out what are the similaties and differences.
Metals and Non-metals
Elements : An element is a substance that is made entirely from one type of atoms. Examples : Hydrogen (H), Helium (He), Oxygen (O), etc.
Classification : Based on their properties they are classified into two categories called metals and non-metals.
Metals : Those elements which possess lustre when freshly cut, are malleable, ductile and good conductors of heat and electricity are known as metals. they may also be defined as those elements which lose electrons and form positive ions. us, metals are electropositive elements. Examples : Sodium (Na), Potassium (K), Calcium (Ca), etc.
Non-metals : Those elements which do not possess lustre and are neither good conductors of heat and electricity nor malleable and ductile but are brittle, are known as non-metals. they may also be defined as elements which gain electrons and form negative ions. Thus, non-metals are electronegative elements. Examples : Hydrogen (H), Oxygen (O), Nitrogen (N), Chlorine (Cl), etc.
Physical properties of metals
- Metals in their pure state have shining surface i.e., possess metallic lustre.
- Metals are generally hard, the hardness varies from metal to metal, if the Stronger the metallic bond are persent metal is hardest.
- Metals are generally malleable, the ability of metals to be beaten into thin sheets is called malleability.
- Metals are generally ductile, the ability of metals to be drawn into wires is called ductility. Gold is the most ductile metal.
- Metals are good conductors of heat and possess high melting points. But some exceptions are there e.g., lithium, sodium, potassium, caesium and gallium are metals with low melting points. Infact, gallium and caesium have so low melting points that they melt even on keeping them on the palm.
- Metals are good conductors of electricity. the order of electrical conductivity of some metals is found to be as follows : Silver(Ag) >Copper(Cu) >Gold(Au) >Aluminium (Al) >Tungsten(W) > Mercury(Hg)
- Metals are sonorous i.e., they produce sound by striking on hard surface.
- Metals have high density due to closely packed atoms. But lithium, sodium, potassium are metals with low densities.
- Metals have high tensile strength, Due to this property, iron is used in the construction of bridges, buildings, railway lines, etc.
- All metals are solids except mercury which is liquid.
Physical properties of non-metals
- Non-metals do not possess any lustre, but iodine is a non-metallic solid with lustre.
- They are so and brittle, the only exception is diamond, an allotropic form of carbon, which is a non-metal but is the hardest substance known.
- They are neither malleable nor ductile.
- They are bad conductors of heat and electricity. Exception is graphite which is an but good conductor of electricity.
- They are non-sonorous, i.e., they do not produce any sound when hit with a hard object.
- They have low melting and boiling points except diamond and graphite which have high melting points.
- They have low densities.
- They have low tensile strength i.e., these are easily broken.
- They may be solids, liquids or gases at room temperature. – Carbon, sulphur, phosphorous and iodine are solid non-metals. – Bromine is a liquid non-metal. – Hydrogen, oxygen, nitrogen, chlorine, helium and neon are gaseous non-metals.
Chemical properties of metals
1. Reaction with oxygen : Almost all the metals react with oxygen or air to form metal oxides which are basic in nature. eg: Metal + Oxygen →Metal oxide
When copper is heated in air, it combines with oxygen to form copper (II) oxide which are show as black colour.
2Cu + O2 →2CuO
Iron reacts with oxygen to give a mixture of FeO and Fe2O3
3Fe + 2O2 →FeO.Fe2O3 or Fe3O4
2. Reaction with water : Highly reactive metals such as sodium and potassium (placed at the top of the reactivity series) react violently even with cold water with formation of hydrogen gas and energy is released.
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) + heat energy
Calcium reacts with water less violently while magnesium reacts with water only on heating.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
Mg(s) + 2H2O(l) + Heat → Mg(OH)2(aq) + H2(g)
3. Reaction with acids : Metals placed above hydrogen in the reactivity series react with dilute acids such as HCl and H2SO4 to displace hydrogen from acids forming corresponding metal salt with the evolution of hydrogen gas. eg: Metal + Acid(dil.) Metal salt + Hydrogen gas
Examples1 : 2Na(s) + 2HCl(dil.) → 2NaCl(aq) + H2(g)
Examples2 : Mg(s) + H2SO4(dil.) → MgSO4(aq) + H2(g)
Hydrogen gas is not evolved when a metal reacts with nitric acid because nitric acid is a strong oxidising agent. Gold and platinum are noble metals which do not react with any strong acid like HCl, HNO3 and H2SO4, but these can be dissolved in aqua regia (a mixture of conc. HCl and conc. HNO3 in the ratio of 3 : 1) due to the formation of nascent chlorine which reacts with these metals to form metal chlorides.
3HCl + HNO3 (Aqua regia) → NOCl + 2H2O + 2Cl
Reaction with salt solutions : More reactive metals can displace less reactive metals from the aqueous solutions of their salts. ese reactions are known as metal displacement reactions.
Generally, Metal A + Salt solution of B → Salt solution of A + Metal B
Examples1 : Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
Examples2 : Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Reactivity series : It is the series in which metals are arranged in the order of their decreasing reactivity as shown :
Potassium (K) >Sodium (Na) >Calcium (Ca) >Magnesium (Mg) >Aluminium (Al) >Zinc (Zn) >Iron (Fe) >Lead (Pb) >Hydrogen (H) >Copper (Cu) >Mercury (Hg) >Silver (Ag) >Gold (Au)
Characteristics of the reactivity series
- Metals are arranged in this series on the basis of the ease with which atoms of these metals give up their electrons to form ions.
- Higher the metal in the series, greater is its tendency to form ions in solution.
- Metals are placed in a decreasing order of reactivity, i.e., the most reactive metals are placed at the top and as we move down, the reactivity of metals decreases.
- The series also shows which metal will displace the other in a solution. Metals placed above will displace the metals placed below in the series
Ionic compounds : A chemical bond formed between two atoms by complete transfer of electrons from one atom to another so as to complete their octets and hence, acquire the stable nearest noble gas conguration, is called ionic bond. e compounds thus formed are known as ionic compounds.
Formation of ionic compounds : During formation of ionic compounds, metal atom looses electrons and these electrons are accepted by non-metal atom.
Properties of ionic compounds
1. Physical state : Ionic compounds are generally solids and exist in the form of crystals as ions are bonded by strong attractive forces.
2. Melting and boiling points : their melting and boiling points are very high as they have strong forces of attraction.
3. Solubility : Ionic compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.
4. Electrical conductivity : Ionic compounds conduct electricity in the aqueous solution as well as in the molten state but not in the solid state.
Occurrence of metals
The major source of metals (whether in the free state or in the combined state) is the earth’s crust. Some metals are found in the sea water in the form of their soluble salts. Percentage of some metals in earth’s crust is as follows : Al(7%), Fe(4%), Ca(3%), Na(2.7%), K(2.5%), Mg(2%) and Ti(0.6%).
Minerals and Ores : The elementary state or the compounds, in the form of which the metals occur in nature are called minerals. the earthy, sandy and rocky impurities associated with the mineral are called gangue or matrix. Also, the mineral from which the metal can be extracted conveniently and economically is called an ore.
Extraction of metals : Getting a metal out of its ore is called extraction of the metal.
Metallurgy
Various steps involved in the extraction of a metal from its ore followed by rening of the metal is called ‘metallurgy’. the steps involved are as given below : There are three major steps involved in the extraction of a metal from its ore
- concentration or enrichment of ore
- conversion of concentrated ore into metal
- rening of impure metal.
1. Concentration or enrichment of ore : It is done by removing gangue the methods for removing gangue are gravity separation, froth oatation process, electromagnetic separation and chemical separation.
2. Conversion of concentrated ore into metal : Extraction of highly reactive metals : The highly reactive metals like Na, Mg, Ca, etc. are extracted by electrolytic reduction of their molten chlorides or oxides. Electrolytic reduction is brought about by passing electric current through the molten state. Metal gets deposited at the cathode.
At cathode : Na+ + e → Na
At anode : 2Cl– → Cl2 + 2e–
Extraction of metals of medium reactivity : The metals with moderate reactivity like zinc, iron, lead, copper, etc. are generally present as oxides, sulphides or carbonates. ese sulphides and carbonates rst need to get converted to oxides as it is easier to get metal from their oxides. is can be done by two processes
- Roasting : In this process, the sulphide ores are converted into oxides by heating strongly in presence of excess of air. 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g)
- Calcination : In this process, the carbonate ores are converted into oxides by heating strongly in the absence or limited supply of air. ZnCO3(s) → 2ZnO(s) + CO2(g)
The metal oxides are then reduced to corresponding metals by using reducing agents like carbon or by using displacement reactions with highly reactive metals such as aluminium, sodium, calcium, etc.
ZnO(s) + C (s) + Heat → Zn(s) + CO(g)
3MnO2(s) + 4Al(s) Heat → 3Mn(l) + 2Al2O3(s)
The reduction of metal oxides to metal using aluminium as the reducing agent is called aluminothermy. The reaction is highly exothermic. the heat evolved is so high that the metal is obtained in the molten state.
Fe2O3(s) + 2Al(s) Ignited → 2Fe(l) + Al2O3(s)
This reaction is known as thermite reaction and used for welding the broken parts of iron machinery, railway tracks, girders, etc.
3. Rening of impure metal : The process of purifying impure metals is called rening of metals. The most widely used method is electrolytic rening. In this process, the impure metal is made the anode and a thin strip of pure metal is made the cathode. A solution of the metal salt is used as an electrolyte. On passing the current through the electrolyte, the impure metal from the anode dissolves into the electrolyte and pure metal from the electrolyte is deposited on the cathode. the soluble impurities go into the solution, whereas, the insoluble impurities settle down at the bottom of the anode as such in the form of anode mud.
Corrosion : The process of slowly eating up of metals due to their conversion into oxides, carbonates, sulphides, sulphates, etc. by the action of atmospheric gases and moisture is called ‘corrosion’. In general, more reactive the metal, more easily it gets corrode. Metals like potassium, magnesium, aluminium, zinc, iron, etc. undergo corrosion easily while noble metals like gold and platinum do not get corroded easily. Corrosion of iron is known as rusting which causes a big loss to the economy of the country.
Prevention of corrosion
Rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys. – A thin layer of tin metal or chromium metal is deposited on iron objects by electroplating to prevent rusting. – Galvanisation is a method of protecting iron from rusting by coating them with a thin layer of zinc.
Alloy : An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal. e.g., stainless steel (Fe + Cr + Ni), brass (Cu + Zn), bronze (Cu + Sn), etc.