Friday, September 9, 2011

CBSE Extra score Notes for: Metals and Nonmetals for VII Science

Metals : The elements that lose electrons and form positive ions are called metals. They are also called electropositive elements. E.g. sodium, potassium, calcium, magnesium, gold, silver, copper, etc.
Hydrogen is a nonmetal but it is placed in the in the group of metals because like metals it also loses electron and forms positive ion.
Physical properties of metals:
Metals are malleable, ductile, hard, good conductors of heat and electricity, and sonorous. They are generally solids and have high melting and boiling points.
Lusture :  The property of an element due to which it has a shiny appearance is called metallic lusture.
Malleability  The property of metals to be beaten into thin sheets is called malleability. Gold and silver are most malleable metals.
Ductility  The property of metals to be drawn into thin wires is called ductility. Gold is most ductile metal.
Followings are exceptional Metal which –
a) Is liquid at room temperature – mercury
b) Are most malleable – gold and silver
c) Are poor conductors of heat -lead and mercury
d) Can be cut with knife – sodium, potassium,lithium
e) Is not malleable and ductile – zinc
f) Have very low melting point – gallium and caesium
g) Is most abundant in earth crust – aluminium
h) React with dil HNO3- Mg and Mn
i) Do not react with water at all – gold, silver,platinum, lead and copper
j) React with steam only aluminum, iron and zinc
k)Do not react with oxygen even at high temperature – gold, platinum, silver
Chemical properties of metals.
a) Metals on burning in air forms basic oxides.
b) Metals displace hydrogen from water and steam.
c) Metals displace hydrogen from dilute acids.
d) Metals form ionic chlorides with chlorine.
e) Metals do not react with hydrogen. ( only few reactive metals react with hydrogen to form hydrides )
Hydrogen gas does not evolve when a metal reacts with nitric acid 
because nitric acid is strong oxidising agent. It oxidises the hydrogen gas produced to water and itself gets reduced to any of nitrogen oxides i.e. N2 O, NO or NO2 .Nonmetals : The elements that gain electrons and form negative ions are called nonmetals. They are also called electronegative elements. E.g. chlorine, sulphur, oxygen, bromine, phosphorus, nitrogen, etc.
Physical and Chemical Properties  
a) Nonmetals are not malleable and ductile but they are brittle.
b) Nonmetals are solid, liquid and gas at room temperature.
c) Nonmetals are not good conductors of heat and electricity.
d) Nonmetals have low melting and boiling points.
e) Nonmetals are soft.
f) Nonmetals form acidic or neutral oxides when react with air
g) Nonmetals do not react with water and steam.
h) Nonmetals do not displace hydrogen with dilute acids.
i) Nonmetals form covalent chlorides with chlorine.
j) Nonmetals react with hydrogen to form stable hydrides.
Followings are exceptional  Nonmetals which 
a) Is liquid at room temperature – bromine
b) Are lustrous – iodine and graphite
c) Is hardest – diamond
d) Are good conductors of electricity – carbon and gas carbon
e) Is most abundant in earth crust – oxygen
f) Show allotropy – carbon, sulphur and phosphorus
g) They do not conduct electricity because they do not contain ions in molten state.
Amphoteric oxides
The metal oxides which show the properties of both acidic oxides as well as basic oxides are called amphoteric oxides. They react with both acids and bases to produce salt and water.
E.g. aluminium oxide and zinc oxide
Al2 O3 + 6HCl -----> 2AlCl3 + 3H2 O ;
Al2 O3 + 2NaOH ---> 2NaAlO2 + H2 O (Sodium aluminate)
ZnO + 2HCl ----> ZnCl2 + H2 O ;
ZnO + 2NaOH ------> Na2 ZnO2 + H2 O (Sodium zincate)
Alloy : The homogeneous mixture of a metal with other metal or nonmetal in molten state is called an alloy.
a) Stainless steel is an alloy of iron, nickel and chromium.
b) Brass is an alloy of copper and zinc.
c) Bronze is an alloy of copper and tin.
d) Solder is an alloy of lead and tin. It has low melting point and is used for welding electrical wires together.
Properties of Alloy:
a) Increase hardness ,                              b) Make resistant to corrosion,     
c) Decrease melting point,                      d) Change chemical reactivity    
e) Decrease electrical conductivity        f) Increase colour and tensile strength
Allotropy and allotropes
The phenomenon in which an element can exist in two or more different physical forms is called allotropy and the different physical forms of an element are called allotropes.Eg.  Allotropes of carbon are graphite, diamond and Buckminster fullerene.
Aqua regia. Aqua regia is the mixture of concentrated hydrochloric acid and nitric acid in the ratio 3:1. It is called ‘Royal water’ because it can dissolve gold and platinum.
Reactivity series :
The series of metals in which they are arranged in order of their decreasing reactivity is called reactivity of activity series.
Reactivity  : The tendency of an element to attain a completely filled outermost shell by losing or gaining electrons is called reactivity.
Ionic compounds  : The compounds formed by losing or gaining electrons or by the transfer of electrons from metal to nonmetal are called ionic compounds or electrovalent compounds. Ionic bonds are formed between metals and nonmetals.E.g. NaCl, MgO, CaCl2, NaOH, Al2O3, etc.
Properties of ionic compounds
a) Ionic compounds are solids and hard because of strong force of attraction between positive and negative ions. They are brittle.
b) Melting and boiling points of ionic compounds are high because a large amount of energy is required to break the inter-ionic attraction.
c) Solution of ionic compound in water contains ions which move towards oppositely charged electrodes when electricity is passed. This is why ionic compounds are very good conductors of electricity.
f) Ionic compounds in a solid state do not conduct electricity because movement of ions in solid state is not possible due to rigid structure. So they conduct electricity only in molten state.
g) The covalent compounds are usually liquids due to the weak forces of attraction between their molecules.
h) They usually have low melting and boiling points because the force of attraction between molecules is very weak and a small amount of energy is required to break these forces.
Minerals :

The elements and compounds which are found naturally in the earth crust are called minerals.Ores  The minerals from which metals can be extracted easily and profitably are called ores. An ore contains good percentage of metals and less impurities.
Rusting:. The process of depositing a brown flaky substance on the surface of iron due to air and moisture is called rusting. The brown substance is called rust. It is chemically Fe2O3.xH2O.
The process of depositing a thick layer of zinc metal on iron objects is called galvanization.
Chrome plating. 
The process of depositing a layer of chromium (Cr) on iron objects is called chrome plating.
The process of making homogeneous mixture of a metal with other metal or nonmetal in molten state is called alloying.

 All ores are minerals but all minerals are not ores because there may be some minerals from which metals cannot be extracted easily and profitably.
Gangue :  The unwanted materials or the impurities like soil and sand present in an ore are called gangue.
Corrosion. : The process of slowly eating away of metals due to their conversion into oxides, carbonates, sulphides, sulphates, etc by the action of moisture and gases is called corrosion
Conditions for rusting are – presence of moisture and presence of air.
Prevention of rusting : Rusting of iron can be prevented
a) by painting, applying grease or oil,
b) galvanization,
c) chrome plating,
d) anodizing,
e) making alloys.
Galvanization:The process of forming a thick layer of zin over other metal is called  Galvanization .
Self protecting metals  : The metals that react with air to form a thin layer of their oxide over them to protect from further corrosion of oxidation are called self protecting metals. E.g. aluminium, zinc, magnesium, lead, etc.
Anodizing : The process of forming a thick layer of aluminium oxide over aluminium metal is called anodizing.
During anodizing process : A clean aluminum article is made anode and is electrolyzed with dil H2 SO4  . The oxygen gas produced at anode reacts with aluminium to make a thicker protective layer of its oxide.

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