Physical properties of metals:
- All metals exist in the solid state at room temperature except mercury which is in the liquid state.
- All metals in their pure state have shining surface and such property if metals are called as metallic lustre.
- Metals are hard and hardness of metal changes from metal to metal.
- Metals possess property of malleability that means they can be beaten into thin sheets. For example, gold and silver are malleable metals.
- Also, metals have ability to be drawn into thin wires and such property is called as ductility. Gold is one of the most ductile metal.
- Metals have high melting points and hence they are good conductors of heat also. Silver and copper are the best conductors of heat while mercury and lead are poor conductors of heat.
- Gallium and caesium are the metals having very low melting point.
Non-metals:
- Carbon, sulphur, iodine, oxygen, hydrogen etc all are the non-metals. All the nonmetals are either solid or gases except bromine which is in liquid state.
- Also, iodine is the nonmetal but it is lustrous.
- Carbon is the nonmetal but it has allotropes. One of its allotropes is the diamond which is the hardest and having very high melting and boiling point also.
- While graphite is another allotrope of carbon but it is a good conductor of electricity.
Chemical properties of metals:
1.) Reaction of metals with oxygen:
- All metals combine with oxygen in air and forms the metal oxides.
- The general chemical reaction can be written as,
Metal + Oxygen —-> Metal oxide
For example:
- When copper is heated in air then it reacts with oxygen and forms a black oxide called as copper oxide and the reaction is as given below.
2Cu + O2 ——> 2CuO
- Also, aluminium reacts with oxygen and forms the aluminium oxide as given in the following chemical reaction.
4Al + 3O2 ——> 2Al2O3
- Metal oxides are basic in nature but some of the metal oxides like zinc oxide, aluminium oxide shows both acidic as well as basic nature.
- These oxides react with both acids and bases and forms the salt and water such oxides are called as amphoteric oxides.
- The reaction of aluminium oxide with acid and base is as given below.
Al2O3 + 6HCl ——> 2AlCl3 + 3H2O
Al2O3 + 2NaOH ——-> 2NaAlO2 + H2O
While oxides of sodium and potassium dissolve in water and forms the alkalis as given below.
Na2O(s) + H2O(l) ——> 2NaOH(aq)
K2O(s) + H2O(l) ——> 2KOH(aq)
- Metals like potassium and sodium are highly reactive and hence they cannot be kept open. If they kept in open space, they may catch the fires instantly. Hence, to prevent accidental fires and protect such metals they must be immersed in the kerosene oil.
- Also, metals like magnesium, zinc, lead, aluminium etc at room temperature undergoes oxidation and to prevent such further oxidation the surface of such metals is covered with the thin layer of oxides.
- Metals like silver and gold does not react with oxygen even at high temperatures also.
2.) Reaction of metals with water:
- All metals do not react with water. But some metals react with water and forms metal oxide and hydrogen gas. If the metal oxides formed further soluble in water, then it reacts with water again and forms the metal hydroxide.
- The general chemical reaction is given as below.
Metal + water ——-> metal oxide + hydrogen
Metal oxide + water ——> metal hydroxide
- The metals like sodium and potassium reacts violently with the cold water and it is exothermic reaction. As they react with cold water forms hydrogen gas which catches fire immediately.
- The reaction is as given below.
- 2K(s) + 2H2O(l) ——-> 2KOH(aq) + H2(g) + heat energy
- 2Na(s) + 2H2O(l) —–> 2NaOH(aq) + H2(g) + heat energy
- The reaction of calcium with water is not more reactive and hence the hydrogen gas produced does not catch the fire.
Ca(s) + 2H2O ——> Ca(OH)2(aq) + H2(g)
- Magnesium does not react with the cold water but it reacts with the hot water and forms the magnesium hydroxide and hydrogen.
- Metals like iron, zinc and aluminium does not reacts with hot or cold water. But they react with the steam to form metal oxide and hydrogen as given in the following chemical reaction.
2Al(s) + 3H2O(g) ——> Al2O3(s) + 3H2(g)
3Fe(s) + 4 H2O(g) ——-> Fe3O4(s) + 4H2(g)
But metals like lead, copper, silver and gold does not reacts with water under any circumstances.
3.) Reaction of metals with acids:
- Metals reacts with the acids and forms salt and hydrogen gas.
Metal + dilute acid —–> salt + hydrogen
- Metals like magnesium, aluminium, zinc and iron reacts with dilute HCl and evolves hydrogen gas.
- But when metals react with nitric acid then hydrogen gas is not evolved as nitric acid is the strong oxidising agent. It again oxidises the H2 produced to form water and self-get reduced to nitrogen oxides.
- But, metals like magnesium and manganese reacts with very dilute nitric acid and evolves the hydrogen gas.
4.) Reaction of metals with solution of other metal salts:
If metal A reacts with the salt solution of metal B then salt solution of metal A and metal B is formed which is shown in the following chemical reaction.
Metal A + salt solution of B ——-> salt solution of A + metal B
The reactivity series:
- The following is the order of reactivity of metals.
- The metals like potassium, sodium , calcium and magnesium are most reactive. The metals like aluminium, zinc, lead, iron is less reactive. While the metals like copper, mercury, silver and gold are least reactive.
- The decreasing reactivity order of metals is as given below.
K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au
5.) Reaction of metals and nonmetals:
- The atomic number of Na is 11.
- Sodium Na has electronic configuration as 2, 8, 1.
- So, Na loses one last electron and its octet become completed. So, Na forms Na+ ion by losing one electron.
Now, Cl has atomic number 17 and electronic configuration as 2, 8, 7. Cl requires only one electron to complete its octet. So, it takes one electron loosed by sodium and forms Cl- ion. The Na+ and Cl- ions formed are oppositely charged and attract each other with a strong electrostatic force of attraction and forms the NaCl molecule as shown in following chemical reaction.
- Similarly, Mg has electronic configuration as 2, 8, 2 and to complete its octet it loses last 2 electrons easily and forms Mg2+
- Two atoms of Cl having electronic configuration 2, 8, 7 takes these two electrons and complete their octet and forms the MgCl2 molecule as shown below
- The compounds which are formed by the transfer of electrons from metal to nonmetal are called as ionic compounds or electrovalent compounds.
Properties of ionic compounds:
1.) Physical nature:
- Ionic compounds are formed by the strong electrostatic force of attraction and hence they are somewhat hard. Some compounds are brittle on which if we applied some pressure they get broken into small pieces.
2.) Melting and boiling point:
- As the ionic compounds are formed due to strong inter-ionic attraction, their bond breaking is requiring more energy. And hence they are having high melting and boiling point.
3.) Solubility:
- Ionic compounds are mostly soluble in water but they are insoluble in solvents like petrol, kerosene etc.
4.) Conduction of electricity:
- The ionic compounds in water have oppositely charged ions which gets attracted towards opposite electrodes and current flows.
- Solid ionic compounds do not conduct electricity but ionic compounds in molten state conducts electricity.
Refining of metals:
Electrolytic refining:
In electrolytic refining process the impure metals form the anode and thin strip of pure metal forms the cathode. And here a solution of metal salt is used as electrolyte. When current is passed through this electrolyte the pure metal from the anode gets dissolved in the electrolyte. And the same amount of pure metal gets deposited on the cathode also. Soluble impurities go into the solution while insoluble impurities remain at the bottom of the anode which we called as anode mud.
Corrosion:
- When silver articles get in contact with air after sometime they become black and this is because silver reacts with sulphur in air and it forms the coating called as silver sulphide.
- Also, copper reacts with the moist CO2 in air and after that it loses its shiny brown surface and green coating is formed on it. This green coating is called as copper carbonate.
- Similarly, iron on contact with moist air for long time there also brown flaky substance coating is formed on it called as rust.
Prevention of corrosion:
- The iron can be protected from rusting by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys.
- When steel and iron are coated with thin layer of zinc they get protected from rusting and such process is called as galvanising.