Elements can be classified into the following two groups depending on their physical and chemical properties:
Metals
Non-metals
Physical properties of Metals:
Metalloids:
The elements which possess the properties of metals and non-metals are called metalloids.
For example: boron, silicon, germanium, tellurium, arsenic and antimony are metalloids.
Chemical properties of Metals and Non-metals:
Reaction with oxygen:
Reaction of metals with oxygen:
Metals react with oxygen under different conditions to form basic oxides. These basic oxides react with water to form bases which turn red litmus into blue.
Sodium and potassium react with oxygen vigorously at room temperature.
4Na + O2 ---> 2Na2 O
To prevent this oxidation, sodium and potassium are stored under kerosene.
agnesium reacted with oxygen only if ignited. It gives a bright dazzling flame and forms a white powder of magnesium oxide.
2Mg + O2 ----> 2MgO
Iron metal does not burn in dry air even on strong heating. In moist air, iron get oxidise to form iron oxide (rust)
4Fe + 3O2 ------> 2Fe2 O3
Fe2 O3 + nH2 O ------> Fe2 O3 nH2 O
Reaction of non-metals with oxygen:
Non-metals react with oxygen to form acidic or neutral oxides.
C + O2 ----> CO2
S + O2 -----> SO2
Other oxides like carbon monoxide (CO) and nitrous oxide (N2O) are neutral.
Reaction with water:
Reaction of metal with water:
etal react with water to form oxides or hydroxides along with hydrogen. Different metals react at different temperature.
Sodium, potassium and calcium react vigorously with cold water to form metal hydroxides.
2Na + 2H2O -----> 2NaOH + H2
etal from magnesium to iron react with steam (but not water) to form metal oxide and hydrogen gas.
2Mg + H2O -----> 2MgO + H2
Tin, lead, copper, silver and gold do not react with water or steam.
Reaction of non-metal with water:
Non-metals do not generally react with water.
Reaction with dilute acids:
Reaction of metals with dilute acids:
Metals react with dilute acids to form their salt and liberate hydrogen gas. The evolution of hydrogen gas can be tested by bringing a burning splinter near the mouth of the test tube. Hydrogen gas will put off the splinter with a pop sound.
2Na + 2HCl ------> 2NaCl + H2
Zn + H2SO4 ------> ZnSO4 + H2
etals below hydrogen (copper, silver, gold and platinum) do not react with dilute acids as they are less reactive than hydrogen. So they cannot displace hydrogen from dilute acids.
Reaction of non-metals with dilute acids:
Non-metals do not react with dilute acids.
Displacement reactions:
A more reactive metal displaces a less reactive metal from its compound in aqueous solution. Such a reaction is known as displacement reaction.
For example: When iron nail put in copper sulphate solution then colour of solution changes from blue to light green and a reddish brown coating of copper is seen on iron nail.
Fe + CuSO4 ---> FeSO4 + Cu
Iron copper sulphate iron suphate copper
(blue) (green)
Iron sulphate + copper no reaction
Because copper is less reactive than iron so cannot displace it.
Uses of metals and non-metals:
Uses of metals:
Copper and aluminium are used to make wires for carrying electric currents.
Zinc is used for galvanising iron to protect iron from rusting.
Silver, gold and platinum are used make jewellery.
Iron, copper and aluminium metals are used to make utensils for cooking and for manufacturing machines parts.
Mercury is used in thermometer.
Lead is mainly used for making electrodes for automobile batteries and for making alloys.
Uses of non-metals:
Hydrogen is used in manufacture of ammonia, industrial chemicals.
Liquid nitrogen is used in refrigerant, in storing human organs at low temperature.
Sulphur is used in manufacture of sulphuric acid, sulphur dioxide gas, sulphur drugs etc.
Sulphur is used for vulcanisation of rubber and making gunpowder.
Phosphorus is used in the manufacture of fertilisers.
Silicon is used for making semiconductors foe which microchips are made.
Chlorine is used for disinfecting drinking water.
Oxygen is used in breathing support system for patients.
The Reactivity Series
Metals along with hydrogen (a non-metal) are arranged in order to their activity in a series, called the activity series or The Reactivity Series
How do metals and non metals reacts
Chemical reactivity of elements is the tendency to attain a completely filled valence shell.
Noble elements has completely filled valence shell,So they show little chemical activity
Metals loose the electron to complete the valence shell and Non-metals gain the electron to complete the valence shell
Element which loose electron become positively charged and called cation
Element which gain electron become negatively charged and called anion
Example
1. Formation of Sodium Chloride
a. Sodium looses the electron to complete the shell and become Na+
b. Chloride gain the electron to complete the shell and become Cl-
Sodium and chloride ions, being oppositely charged, attract each other and are held by strong electrostatic forces of attraction to exist as sodium chloride (NaCl). It should be noted that sodium chloride does not exist as molecules but aggregates of oppositely charged ions
Ionic Compounds
The compounds which are found by transfer of electron from Metals to non metals like given above with Sodium chloride is called ionic compounds
Examples: NaCl, MgCl2 Properties
a. Physical nature: Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive
and negative ions. These compounds are generally brittle and break into pieces when pressure is applied
b. Melting and Boiling points:Ionic compounds have high melting and boiling points
c. Solubility: Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc
d. Conduction of Electricity: ionic compounds conduct electricity in the molten state but not in solid state
Occurence of Metals
Important terms Mineral: The elements or compounds in the form of which metal occur naturally in the earth's crust are called minerals. Ores: Those minerals from which metals can be profitably extracted are called ores .
Metallurgy: The Processes involved in the extraction of metals from ores and refining them to get pure metals are called Metallurgy
There are three steps involved in extraction of metals from Ores
(a)Encrichment of Ores
(b)Extraction of Metals
(c) Refining of Metals
Encrichment 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 methods depends on the differences between the physical or chemical properties of the gangue and the ore
Various Methods are
Extraction of Metals
It is also called the reduction of metal from ore. We use different method based on Activity series
(i) Extracting Metals Low in the Activity Series
Metals low in the activity series are very unreactive. The oxides of these metals can be reduced to metals by heating alone
For example
cinnabar (HgS) is an ore of mercury
When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating.
2HgS(s) + 3O (g) -> 2HgO(s) + 2SO (g)
2HgO(s) -> 2Hg(l) + O (g)
(ii) Extracting Metals in the Middle of the Activity Series
Here the metals are first converted into oxides using Roasting and Calcination and then metals are extraced using Reducing agent like Carbon
(a) Roasting: The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting
2ZnS(s) + 3O (g) -> 2ZnO(s) + 2SO (g)
(b)Calcination: The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination
ZnCO3 (s) -> ZnO(s) + CO (g)
(c) Reduction
when zinc oxide is heated with carbon, it is reduced to metallic zinc.
ZnO(s) + C(s) -> Zn(s) + CO(g)
Sometimes highly reactive metals such as sodium, calcium, aluminium, etc., are used as reducing agents because they can displace metals of lower reactivity from their
compounds.
(iii) Extracting Metals towards the Top of the Activity Series
The highly reactive metals are obtained by electrolytic reduction. For example, sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides. The metals are deposited at the cathode (the negatively charged electrode), whereas, chlorine is liberated at the anode (the positively charged electrode).
At cathode Na+ + e- -> Na
At anode 2Cl- -> Cl2 + 2e-
Refining of Metals
The metals after extraction is not pure and we have to refine it to obtain pure metal.We use Electrolytic Refining for this purpose
Example of metals which are refined using this method are copper, zinc, tin, nickel, silver, gold, etc.
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 pure metal from the anode dissolves into the electrolyte. An equivalent amount of 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 and are known as anode mud.
Corrosion
Corrosion is the process of eating up of metal surface by air, moisture or a chemical.
Example
(a)Silver articles become black after some time when exposed to air. This is because it reacts with sulphur in the air to form a coating
of silver sulphide.
(b) Copper reacts with moist carbon dioxide in the air and slowly loses its shiny brown surface and gains a green coat. This green
substance is copper carbonate.
(c)Iron when exposed to moist air for a long time acquires a coating of a brown flaky substance called rust
Prevention of Corrosion Fill in the blanks:
Metal react with oxygen to produce ................oxides and non-metal react with oxygen to produce................oxides.
The presence of .............. and ..................are necessary for iron to rust.
...................is used for making X-ray shields.
.....................non-metals is used in fluorescent bulbs to display advertisements.
....................element is used for making pencil lead.
.....................is the only non-metals that exist as liquid at room temperature.
The property of metals by which it can be beaten into sheets is called.................
.....................metal can be cut with knife.
......................non-metal is used for vulcanisation of rubber.
.......................metal is used in processed food packaging.
Process of coating metals with zinc is called.......................
Elements that possess properties of both metals and non-metals are called.............
....................is a pure chemical substance consisting of only one type of atoms.
Metal react with dilute acids to form...................... and.......................
Answer:
Basic, acidic
Air, water
Lead
Neon
Graphite
Graphite, iodine
Bromine
Malleability
Sodium
Sulphur
Nitrogen
Galvanization
Metalloid
Element
Salt, hydrogen gas
Short answers:
Why is gold used for making jewellery?
Gold does not easily react with other substances. It is an unreactive metal and once polishes, it retains their shine for a long time, therefore, it is used for making jewellery.
What do you mean by corrosion?
Corrosion is used to describe the process by which minerals such as metals are slowly eaten away when exposed to air and moisture.
No gas is released when sulphur is added to dilute HCl?
No gas is releases when sulphur is added to dilute HCl because non-metals do not react with dilute HCl and sulphur is a non-metal.
Why are electrical cables made from copper?
Since copper is a good conductor of electricity, it is used in electrical cables.
Why do copper vessels develop a greenish layer when exposed to moist air?
Copper vessel gets corroded in the presence of moist air that is carbon dioxide and water to form green coating of a substance called basic copper carbonate.
Which non-metal is considered to be backbone of the electronics industry?
Silicon is considered to be the backbone of electronics industry.
Why is sodium metal stored under kerosene?
Sodium metal which react vigorously with the oxygen present in air at room temperature to form sodium oxide. Hence, sodium is stored under kerosene to prevent its reaction with oxygen and moisture present in air.
Write the difference between metal oxides and non-metal oxides?
Metal oxides formed are basic in nature, when dissolved in water they form bases which turn red litmus into blue whereas non-metal oxides are acidic in nature, when dissolve in water they form acids which turn blue litmus into red.
Silver is more likely to tarnish near a petroleum refinery than in a place far away? Explain why?
Silver does not get easily corroded in unpolluted air, however, if the air is polluted with sulphur compounds such as hydrogen sulphide then silver reacts with it to form a black coating of silver sulphide.
What are noble metals?
Silver and gold are present at the bottom of the reactivity series of metals. They are unreactive metals and do not react with water, acids and alkalis. They therefore, occur n free state in nature. So they are noble metals.
