28 August 2015

Chapter 3 Metals and Non-metals

CBSE NCERT Class X (10th) | Science

Chapter 3 Metals and Non-metals

Metals and Non-metals

In general metals can be defined as the elements which have a tendency to lose electrons and form positively charged ions or cations. 

Example: sodium has an electronic configuration of 2,8,1. During a chemical reaction, sodium can lose an electron to a non-metal like chlorine to form a sodium ion that has an electronic configuration of 2,8.

Physical properties of metals:

Physical state:
        •  All metals are solids at room temperature, for example, iron and copper. The one exception is mercury, which is a liquid.

Lustrous nature:
        •  All metals are lustrous. Metal surfaces shine when they are freshly cut. 
Example: Gold and silver are popularly used for making jewellery because of their lustrous nature.

        •  Metals have high densities and, therefore, tend to sink in water. 
Example: Tin and lead sink in water. 
Exceptions to this rule are lithium, sodium and potassium. The density of these elements is lower than that of water and hence they do not sink

        •  Metals are highly malleable, and can be beaten into thin sheets. 
Example: Aluminium and zinc can be rolled into thin sheets. This property makes them suitable for use in various industries like construction and manufacturing.

        •  Metals are highly ductile and can be drawn into wires. For example, copper and silver can be drawn into thin wires.

        •  Metals are good conductors of heat and electricity. Copper wires are commonly used in electric cables because of this property.

Melting point:
        •  Metals have high melting points. 

Example: Tungsten has a high melting point, due to which it is used in bulb filaments. 
Mercury is an exception to this property, since it has a low melting point.

Chemical properties of Metals:Metals react with non-metals to form ionic compounds. 
Example: Sodium reacts with chlorine to form sodium chloride.
            2Na + Cl2  → 2NaCl

Reaction of metals with oxygen:Most of the metals combine with Oxygen to form basic metal oxides. 
Example: When magnesium burns in oxygen it forms magnesium oxide.
             2Mg + O2 → 2MgO

Metal oxides of alkali metals soluble in water to form hydroxide solutions, called alkalies. 
Example: Sodiumoxide soluble in water to form sodium hydroxide.
             2Na2O + H2O →2 NaOH

Reaction of metals with water:Sodium, potassium reacts vigorously even with cold water.
             2Na + 2H2O → 2NaOH + H2
             2K + 2H2→ 2KOH + H2

Calcium reacts slowly with cold water. And can react vigorously with hot water.
             Ca + 2H2 Ca(OH)2 + H2

Magnesium does not reacts with cold water. It reacts very slowly with hot water but reacts vigorously with steam.
             Mg + 2H2O → Mg(OH)2 + H2

Iron and zinc do not react either with cold or hot water but react with steam.
             Zn + H2→ ZnO + H2
             Fe + H2 FeO + Fe2O3 + H2

Aluminum do not reacts either with cold water, hot water and even steam because of its protective oxide layer.
Metals like Lead, Copper, Gold and Silver do not show any reaction with water.

Non-metals:Non-metals are elements that have a tendency to accept electrons to form negatively charged ions or anions. 
Example: Chlorine has an electronic configuration of 2,8,7. During a chemical reaction, chlorine can accept an electron from a metal like sodium to form a chloride ion. A chloride ion has an electronic configuration of 2,8,8.

Physical properties of non-metals: Physical state:
Non-metals exist as solids, liquids and gases.

Example: Silicon and carbon are solids; bromine is a liquid; chlorine, fluorine and oxygen are gases.

Lustrous nature:
Non-metals are non-lustrous and have a dull appearance 
in nature.

Most of the non-metals have very low density. 

Example: Oxygen and nitrogen are lighter than air. 
Exception is diamond, a form of carbon. Diamond is one of the strongest known substances.

Non-metals are not malleable. 
Non-metals are bad conductors of heat and electricity. 
Exception is graphite, a form of carbon which is a good conductor of electricity.
Non-metals have low melting and boiling points. 

Example: Sulphur and Phosphorus have low melting and boiling points.

Chemical properties of non-metals:Formation of covalent compounds:
Reaction between non-metals produces covalent compounds.

Example: Hydrogen and chlorine reacts with each other form hydrogen chloride       
         H2 + Cl2 → 2HCl

Reaction of non-metals with oxygen:
Non-metals reacts with oxygen to form oxides which are either acidic or neutral in nature.
Sulphur reacts with oxygen to form sulphur dioxide which is acidic in nature
     S + O2 → SO2
Nitrogen reacts with limited supply oxygen to form nitric oxide which is a neutral oxide in nature.
    N2 + O2 → 2NO

Non-metal oxides dissolves in water to form acidic solutions.
Sulphur dioxide dissolves in water to form sulphurous acid.
     SO2 + H2O → H2SO3

Non-metals are good oxidizing agents.
Example: Sulphur in hydrogen sulphide undergoes oxidation when hydrogen sulphide reacts with chlorine. 
     H2S + Cl2 → 2HCl + S

Metals and non-metals are separated through electrolysis

Activity Series

The arrangement of metals in the decreasing order of their reactivity is known as activity series. In the activity series highly reactive metals placed at the top and least reactive metals placed at the bottom.

Gold placed at bottom of the series is the least reactive among the metals and potassium placed at the top is the highly reactive metal.  Hydrogen is the non-metal included in order to compare the reactivity of metals.

The metal placed higher in the series can displace the other metal from its salt solution. Thus potassium can displace all other metals from their salt solutions.

Example: Potassium can displace hydrogen from the acids.

        2K + 2HCl →2KCl + H2

CBSE NCERT Class X (10th) | Science, Chapter 3 Metals and Non-metals, NCERT CBSE Solved Question Answers, KEY NOTES, NCERT Revision Notes, Free NCERT Solutions Online

Metals of low reactivity cannot displace high reactive metals from their salts. For this reason oxides of highly reactive metals like magnesium and aluminium are not reduced easily either by hydrogen, carbon or carbon monoxide. 
Metals that are placed below copper do not rust easily because of their low reactivity. 

Reactivity towards oxygen:On moving down in the reactivity series the reactivity with oxygen decreases.
Metals like potassium, sodium, calcium, magnesium and aluminium can react with oxygen at room temperatures.

Potassium can react with oxygen to form its super oxide in addition to oxide.
K + O2 → KO2
4K + O2 →  2K2O

Sodium on reaction with oxygen forms metal oxide as well as metal peroxide.
4Na + O2 → 2Na2O
2Na + O2 →  Na2O2

Calcium, magnesium and aluminum on reaction with oxygen forms their metal oxides.
2Ca + O2 → 2CaO
2Mg + O2 
→ 2MgO
4Al + 3O2 → 2Al2O3

Reactivity towards water:While moving down in the activity series the reactivity towards water decreases.
Potassium, sodium and calcium can reacts vigorously even with cold water with the liberation of hydrogen gas.
K + H2O → KOH + H2
Na + H2O → NaOH + H2
Ca + H2O → Ca(OH)2 + H2

Magnesium reacts very slowly with cold water but can reacts vigorously with hot water to produce hydrogen gas

Mg + H2→ MgO + H2

Metals like aluminium, zinc and iron does not reacts with cold water or warm water but can reacts with hot steam.
2Al + H2
→ Al2O3 + H2
Zn + H2→ ZnO + H2
3Fe + H2→ Fe3O4 + H2

Reactivity towards mineral acids:

The metals which are present above hydrogen in the reactivity series can reduce hydrogen ions from the acids like HCl and H2SO4. Reactivity decreases on moving down the group in the series.
Potassium, sodium reacts vigorously with dilute acids to liberate hydrogen gas.
K + 2HCl → 2KCl + H2
Na + 2HCl → 2NaCl + H2

Calcium, magnesium also reacts vigorously but slowly with acids libearating hydrogen gas.
Ca + 2HCl → CaCl2 + H2
Mg + 2HCl → MgCl2 + H2

Metals below to hydrogen in the series does not liberate hydrogen on reaction with concentrated or diluted acids.

Metals are available in the form of their ores. 
Ore is a mineral which contains high percentage of metal from which a metal can be extracted most economically.

Methods of extraction of metals from ore  are based on the reactivity of metals.

Methods of extraction:

        •  Reduction
        •  Electrolysis

Reduction is the process of removal of oxygen for extraction of metals from their oxide ores. The common reducing agents used for reduction of metal oxides are:
        •  Carbon monoxide
        •  Carbon
        • Hydrogen

During the extraction of iron from its oxide:
Iron oxide is reduced to iron by carbon monoxide.
      FeO + CO → Fe + CO2

Iron oxide is reduced to iron using carbon as the reducing agent.
      FeO + C → Fe + CO

During the extraction of copper from its oxide:
Copper oxide is reduced to copper using carbon as the reducing agent.

      CuO + C → Cu + CO

Copper oxide is reduced to copper using hydrogen as the reducing agent.
      CuO + H2 → Cu + H2O

But oxides of potassium, sodium, lithium, barium,calcium, magnesium and aluminum cannot be reduced by using carbon, carbon monoxide and hydrogen because of their high affinity for oxygen.

Important ores of Aluminium:

        •  Bauxite: Chemial formula is:  Al2O3.2H20
        •  Bauxite is the principal ore of aluminium.
        •  Corundum: Chemial formula is: Al2O3 
        •  Cryolite: Chemial formula is: Na3AlF6.

The extraction of aluminium from bauxite involves three steps:
        •  The purification of bauxite using Bayer’s process.
        •  The electrolytic reduction of anhydrous Al2O3 by Hall and Herault’s process.
        •  The last step is the purification of impure aluminium by Hoope’s process  

Aluminium is used in:
        •  Manufacture of automobile components
        •  Construction process
        •  Manufacture of electric wires
        •  Packing medicines and pharmaceutical products
        •  Manufacture of soft drink cans and espresso coffee makers
        •  Manufacture of utensils

An alloy is a homogeneous mixture of solid solution of two or more metals or metals with non-metals.

Duralumin is a light and tensile alloy of aluminium. Duralumin is used in the making of air craft frames, pressure cookers. 
Magnalium is an alloy of aluminium and magnesium. Magnalium is used in the making of balances because of its high structural strength and resistance to corrosion. It is also used in the making of optical instruments like cameras and microscopes due to its light weight and resistant to corrosion

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