NOTES PREPARED BY
ASHAQ HUSSAIN BHAT
TEACHER SCHOOL
EDUCATION DEPARTMENT
JAMMU AND KASHMIR
METALS AND NON METALS
2nd BLOG
Cause of chemical combination?
"OR"
Why do metals and non metals react?
Two theories or concepts are used to explain the cause of chemical combination these are:-
(i)Tendency of the atoms to acquire the stable nearest noble gas electronic configuration (Electronic theory or octet rule). This theory was given by Kossel and Lewis. The noble gases have eight electrons (octet) in their valence shells except helium which has two electrons (duplet) and are chemically less reactive. This configuration was regarded as extra stable electronic configuration.
The à toms of all other elements have less than eight electrons in their valence shells and are reactive in nature. The atoms of these elements combine with each other with the re distribution of electrons in the valence shells so that they acquire the stable nearest noble gas configuration (duplet or octet).
(ii) Tendency to acquire a state of minimum energy (modern concept), According to modern concept, the atoms of various elements combine with each other only if the chemical combination leads to the decrease in the energy of the system if on Chemical combination the energy of the system increases, no bond is said to be formed between them.
What are the different modes of chemical combination? OR How do atoms combine?
Ans. To acquire stability, all atoms tend to complete their octets (i.e. outer most shell with eight electrons) or duplet (ie, other most shell with two electrons) if K-shell is the outer most shell. As a result, they acquire the nearest noble gas configuration and ,hence become stable. When the atoms combine, they complete their octet or duplet by any one of the following methods.
1. By transfer of one or more electrons from valance shell of one atom to the other forming an electrovalent (or ionie) bond.
2.By mutual sharing of one, two or three pairs of electrons between two atoms forming covalent bond.
3. By sharing one electron pair in which the shared electron pair is contributed by only one of the combining atoms resulting in the formation of a co-ordinate or dative bond.
What is electron dot structure? Give electron dot structure of some elements.
Ans. In the formation of a chemical bond between two atoms, only the electrons of outer most shell are involved. These electrons present in the outer most shell are called valence electrons.
G.N. Lewis introduced a simple method of representing the valence electrons by dots or small crosses around the symbol of the atom. These symbols are known as electron dot symbols or Lewis symbols. A' few examples of given below:
What is ionic or Electrovalent bond?
It is the chemical bond formed between the two atoms by the transfer of one or more electrons from the valence shell of one atom to the other. This bond is formed between metal atoms and non-metal atoms. One of the combining atoms (metal atom) loses one or more electrons and becomes cation. The other atom (non-metallic atom) gains one or more electrons and becomes an anion. The cation and anion attract each other and are held together by strong electrostatic forces of attraction called ionic bond or electrovalent bond.
What are electrovalent (or ionic) compounds? Explain in light of formation of some ionic compounds.
The compounds formed as a result of the transfer of electrons from one atom of an element to one atom of another element are called ionic or electrovalent compounds e.g. NaCl, MgCl2 KCl etc. To illustrate the formation of ionic compounds, a few examples are given below:-
II Formation of sodium chloride (NaCl).
Atomic member of sodium, Na = 11 its electronic configuration, = 2, 8, 1
Atomic number of chlorine, Cl = 17 its electronic configuration = 2, 8, 7.
During the formation of sodium chloride, one electron is transferred from valence shell of sodium to valence shell of chlorine atom. The transfer of electron from sodium to chlorine may be represented as follows:-
Na +Cl or Naci---------->Na+CI-
This can be represented by writing complete structure of the atoms involved in the bond formation as under
Sodium Atom (Na) Chlorine Atom (CI) Sodium Chloride (NaCl) (Molecule)
(ii) Formation of potassium chloride (KCI)
Atomic number of potassium, K=19 electronic configuration of K=2, 8, 8, 1. it loses the valance electron to form K+ ion and attains the nearest noble gas configuration as that of argon (2, 8, 8)
Atomic number of chlorine =17 electronic configuration of CI = 2,8.7 it gains one electron in valence shell to form Cl- and attains nearest noble gas configuration of argon thus, formation of Kcl, by transfer of electron from K to Cl may be represented as follows:-
K + Cl------------------>K+ Cl-
Potassium atom Chlorine atom Potassium Chloride
Formation of magnesium chloride (MgCl2).
Atomic number of magnesium (Mg) =12 its electronic configuration = 2.8.2. it loses
two electrons from the valence shell to acquire the nearest noble gas configuration. Of neon (2.8) and form Mg2+ion. Atomic no of Chlorine (CI) = 17. it needs only one electron in the valence shell to acquire the nearest noble gas configuration of argon (2,8,8) and form chloride ion (CI-) therefore, the transference of two electrons from one magnesium to two chlorine atoms takes place this can be represented as follows:-
Cl Cl-
Mg + ----------------> Mg²+
Cl Cl-
Magnesium atom chlorine atom Potassium Chloride
Formation of Magnesium oxide (MgO):-
Atomic number of magnesium (Mg) = 12 its electronic configuration = 2,8, 2. It loses two electrons to acquire stable configuration of neon (2,8) and form Mg2+ ion. Atomic No. of oxygen (O) = 8 Its electronic configuration = 2, 6. it gains two electrons in the valence shell to acquire the stable configuration of neon (2,8) and form 0²-ion. Thus, in the formation of magnesium oxide, two electrons are transferred from magnesium atom to oxygen atom as represented below:-
Mg + 0------------------> Mg 2+O²- Or MgO
Magnesium "Oxygen Magnesium oxide.
Give some important properties of ionic compounds.
Some of the important properties of ionic compounds are as follows:-
1) Physical state:- Most of the ionic compounds are crystalline solids. They are relatively hard because of strong electrostatic forces of attraction between the oppositely charged'ions. They are britle and break into pieces on applying force.
2)Solubility:- They are soluble in water but insoluble in organic solvents such as alcohol, petrol, kerosene oil etc.
3) Melting points and boiling points:- They have high melting and boiling points.
4) Most of the ionic Salts:- When brought into the flame, ionic compounds impart characteristic colours to the flame. e.g. sodium chloride imparts golden yellow colour, potassium salts impart. Violet colour and barium salts impart green colour to the flame.
5) Electrical conductivity:- upon dissolving in water ionic compounds dissociate in to free ions. As these ions can conduct electricity, therefore ionic compounds conduct electricity in the aqueous solution.
How do metals Occur in nature?
Metals are found to occur in the nature either in free state (also called native state) or in the combined state i.e. in the form of their compounds. This is because of the fact that different metals possess different chemical re-activities.
1. Free or Native State:- The metals at the bottom of the activity series are least reactive therefore, these are not attacked by moisture, oxygen and carbon dioxide in the air. Thus they occur in the native state. e.g. Gold and platinum.
2. Combined state:- The metals at the top of the activity series (K, Na, Ca, Mg etc.) are highly reactive. Therefore, these are easily attacked by moisture, oxygen and carbon dioxide of the air. They occur in the combined state in the form of their compounds called minerals.
The metals in the middle of the activity series (AI, Zn, Fe, Pb, etc.) are found in the earth's crust mainly as oxides, sulphides or carbonates.
Where from the metals are obtained in nature? Give their relative abundance in nature?
Ans. The major source of metals (whether in free state or combined state) is the earth's crust. Some metals (Na, K etc) which form soluble salts (like NaCl, Mgcl.) are also found to occur in the sea water in the form of their soluble salts. The most abundant metal on the earth's crust is aluminum (about 7%) followed by iron (about 4%)calcium (3%) sodium (27%) potassium (2.5%) magnesium (2%) and titanium (about 0.6%). The remaining metals are present on the earth's crust in very small amounts.
Write note on:-
1.Mineral
2 .Ore
1.Mineral:- The elementary state or the compounds in the form of which the metals occur in nature are called minerals. When these minerals are mined from the earth's crust, they are always contaminated with earthy, sandy and rocky impurities. These earthy, sandy and rocky impurities associated with the mineral are called gangue or matrix.
2. Ore:- The mineral from which the metal can be extracted conveniently and economically is called ore. All minerals are not ores. The ores of some common metals are given below:-
The ores of some common metals are given below:-
Metal./ Name of ore / Name of compound /Formula of the ore
present in the ore
. 1Sodium (Na) / Rock Salt /Sodium Chloride / NaCl
2. Calcium (Ca) / Dolomite /Calcium Magnesium / CaCO3 , MgCO3
carbonate
3. Aluminium (AI) /Bauxite /Aluminium Oxide / A1203.2H20
4. Copper (Cu) /i. Cuprite /Copper (i) Oxide /Cu2o
/ii. Copper glance /Copper (i) sulphide / Cu2S
/iii. Copper Pyrite /Copper Iron sulphide /Cu Fe S
5. Iron (Fe)i /. Iron Pyrite / Iron sulphide / FeS₂
/ ii. Hematite / Iron (iii) oxide / Fe₂O₃
6. Zinc (Zn) /i. Zinc Blend /Zinc Sulphide / ZnS
ii. Calamine /Zinc Carbonte ZnCO;
7. Mercury (Hg) /Cinabar /Mercury (ii) Sulphide /Hgs
8. Silver (Ag) /Argentite /Silver sulphide / Ag₂Sa
9. Lead (Pb) /Galena /LeadSulphide / PbS
What is metallurgy? Describe in detail the various process involved in
The various steps involved in the extraction of the metal from its ores followed by refining of the metal is called metallurgy. The actual process employed for the extraction of a particular metal from its ore depends upon a number of factors e.g.
(i) Nature of the ore. Nature of the impurities present.
(ii) Nature of the metal to be extracted.
The three main steps involved in the extraction of any metal are:-
1. Enrichment of the ore or Concentration of the ore
2. Extraction of the metal from the concentrated ore.
3. Refining of the impure metal.
1:- concentration of the ore or enrichment of the ore:- The process of removal of gangue from the powdered ore is called concentration of the ore or enrichment of the ore or ore dressing. The method used for the concentration of the ore depends upon the nature of ore and nature of impurities present in the ore.
The two main methods employed are:
i. Physical method
ii. Chemical method
1. Physical method :- Physical method of concentration of ore is of following types
Gravity separation or hydraulig washing:- This method is used for the concentration of oxide ores of heavy metals such as lead, tin, iron ete, the method is based upon the difference in the densities of the ore and the gangue, The powdered ore is spread on special type of table having grooves on the top. A stream of water is thrown from one side of the table. The gangue particles being lighter are washed away with the stream of water leaving behind heavy ore particles on the table,
Froth floatation process:- This method is base upon the principle that the ore particles are preferentially wetted by oil where as gangue. Particles are preferentially wetted by water. This method is used for concentration of sulphide ores of copper, Zine and lead The powdered ore is mixed with water in a large tank, then some pine oil or ethyl xanthate is added to it. The mixture is agitated with air. The lighter ore particles are wetted by the oil and form a froth. The froth being lighter floats on the surface. Then the froth formed is transferred to another tank. However, the gangue particles being heavier settle at the bottom of the tank..
Magnetic separation:- This method is based upon the principle that the magnetic particles are attracted by a magnet where as non-magnetic particles are not attracted by a magnet and get separated. The powdered ore is placed on a leather belt which passes over two rollers, one of which is magnetic and other is non magnetic. when the magnetic particles
2:-Chemical separation or by leaching - it is based upon the principle that sangue and ore have different properties and behave differently towards a chemical reagent, In this case, the powdered ore is treated with a suitable reagent (like acid, base etc.) which dissolves the ore particles where as gangue is ten behind and are removed by filtration. This process is called leaching, For example, bauxite ore (AI, O, 211,0) can be concentrated by this method. The powdered bauxite ore is heated with concentrated (45%) sodium hydroxide. As a resalt, aluminium oxide present in the ore reacts with NaOH solution to form water soluble sodium,aluminate.
Al ²O³ + 2NaOH--------------->2Na AlO2 + H2O
Silica present in the ore also reacts with NaOH to form water soluble sodium silicate
SiO2 + 2Na OH------------>Na2 SiO3+H2O
Iron oxide present in the ore does not dissolve in NaOH and thus remains as insoluble. It is separated out by filtration. The filtrate containing sodium aluminate and sodium silicate is diluted with water and stirred.
Sodium aluminate reacts with water to form a precipitate of aluminium hydroxide where as sodium silicate does not react and remains in the solution.
Na AlO2 + 2H2O--------------->Al(OH)3 + NaOH
The PPT is washed, dried and then heated strongly. It decomposes to give pure alumina.
Strong
2Al(OH)3--------------->-Al2O3 + 3 H2O
Heating
2.Extraction of the metal from the concentrated ore:- The method used for the extraction of the metal from the concentrated ore depends upon the nature of the metal. Based on their reactivity, the metals have been grouped into the following three categories.
a. Metals of low reactivity (low in the activity series)
b. Metals of medium reactivity in the middle of the activity series)
c. Metals of high reactivity (At top of the activity series)
c. Metals of high reactivity (At top of the activity series)
(a)Extraction of metals low in the activity series (Cu, Hg, Ag, Au, Pt)
Among these metals gold and platinum are found in their native states taking examples of Cu and Hg, the basic principles of their extraction from the concentrated ore are explained below:-
As their most common ore are sulphides therefore, the step required for extraction is roasting. As a result metal sulphides are converted into metal oxides, the oxides formed on further heating are reduced to metals. For example:-
2HgS + 302--------2HgO +2S02
(Cinnabar ore of Hg)
Heat
2Hgo-------------2Hg + O2
Similarly,
2 Cu2S + 302---------------->2Cu20 + 2S02
2 Cu2O + Cu2 S--------------->6Cu + SO2
b. Extraction of metals in the middle of the activity series (Fe, Zn, Pb etc.)
These metals are found in nature in the form of their oxides, sulphides and carbonate ores. Further, as it is easier to reduce oxides than sulphides and carbonates, therefore, the sulphide and carbonate ores are first converted into the corresponding metal oxides. The different steps involved are as follows:
(i) Calcination ( For carbonate ores):- It is the process of heating the carbonate ore
strongly in the absence of airt so as to form metal oxide e.g.
Zn GO3------Heating--------------->ZnO + CO2
(Calamine ore
of Zinc)
(ii) Roasting (for sulphide ores):- It is the process of heating the sulphide ore strongly in presence of air.
2Zn S -302-----Heating------->2ZnO + 2S02
Presence of air
The metal oxides obtained above can not be reduced alone into their corresponding metals. Therefore, a suitable reducing agent such as carbon (Coke) is used. e.g.
Fe2O3 + 3C-----∆-------2Fe + 3CO
Zn 0 + C----------------------> Zn + CO
The reduction of metal oxides by heating with coke is called smelting.
However, the oxides of metals like chlorine and manganese can not be reduced by using çoke. Therefore, such metal oxides are reduced by strongly heating the mixture with aluminium e.g.
CrO3 + 2Al--------------> 2Cr+ Al2O3
3 MnO2 + 4 Al------------> Mn+ 2Al2O3
The reduction of metals oxides to metal'using aluminium as reducing agent is called as aluminothermy.
b. Extraction of metals High up in the activity series (K, Ca, Mg, and Al)
( Electrometallurgy):- The process of extraction of the metal from the concentrated ore using electric current or by electrolysis is called electro metallurgy. The highly electro positive metals such as Li, Na, K, Ca, Mg etc are extracted by this method. These metals are extracted by the electrolysis of their molten halide or oxides. The metal is produced at cathode. e.g. sodium is obtained by the electrolysis of molten Na Cl.
2NaCl------------------->2Na+ + 2Cl-
At cathode
2 Na + 2e----------------->2 Na
At Anode
2C1- + 2e---------------------->2C1
2CI--------------------------------->Cl2
The active metals can't be obtained by reduction of their oxides with coke because these metal oxides are very stable. Similarly electrolysis of AlO; can be represented as follows:
At Cathode.
ΑΙ³+ + 3e- ---------->Al
At anode
O2- + 2e------------->O
O + O ----------------------->02
3.Refining of impure metals:- The process of purifying the impure (crude) metal is called refining of the metal. The most commonly employed method for the purification of metals is electrolytic refining. A large number of metals such as copper, silver, gold, nickel, chromium, zinc, aluminium, tin, lead etc are purified by this method. To understand the process. let us take the example of electrolytic refining of copper.
To follow up the procedure, a container called electrolytic tank is taken. In this tank a solution of copper sulphate is taken as an electrolyte. The impure copper is taken as anode. A thin plate of pure copper acts as cathode. On passing electric current. pure copper from the anode passes into the solution as Cu ions. An equivalent amount of
Cu²+ ions from the solution are deposited on the cathode as pure copper. The reactions that take place at cathode and anode are shown as follows:-
At Anode
Cu------------------------>Cu²+ + 2e
Copper atom Copper ions
At Cathode
Cu²+ +2e- -------------->Cu
What is activity series?
The arrangement of metals in order of their decreasing reactivity with respect to each other is called activity series of metals. A part of this series is as shown below
What is corrosion? Understand by suitable examples.
Ans. The process of slow eating up (decay) of metals due to their conversion into oxides. carbonates, sulphides, sulphates etc. by the action of atmospheric gases and moisture is called corrosion. A few examples of corrosion are given below:
i.)When iron is exposed to moist air for a long time, its surface gets covered with a coating of a brown, flaky (or non-sticky) substance called rust. This is due to the reaction of oxygen and moisture (present in the air) on the surface of iron. Rust is mainly hydrated ferric oxide.
2Fe + 3/2 02 + X H2O------------->Fez O3, X HO
Iron air moisture (Rust)
(Ii) Similarly copper objects when remain exposed to air, their surface reacts with CO, and moisture present in the air forming a green carting of basic copper carbonate.
2Cu + CO2 + O2 + H2O--------->CuCO,+Cu(OH)2
Copper From moist air (Basic copper green).
(iii) The surface of silver metal gets furnished on exposure to air. This is due to the formation of a coating of black silver sulphide (Ag2S) on its surface by the action H2S gas present in air.
2Ag + H²S------------------->Ag₂S + H2
Silver silver Sulphide(Black)
What is Rusting? State the conditions necessary for rusting.
Ans. Corrosion of iron is called rusting i.e. when iron is exposed to moist air for a long time, its surface acquires a coating of a red brown flaky substance called rust. Rust is mainly hydrated iron oxide. (Fe203 X H2O)
During rusting of iron, iron metal combines with oxygen of air in presence of moisture to form hydrated iron oxide. The number of molecules of water varies in it. but is not fixed. Rust can be commonly observed in the form of red brown flaky substance on screwe, nails, pipes and railings. It is not only the iron which rusts, even the steel rusts on being exposed to damp air or on being kept in water but steel rusts less readily than iron.
The conditions necessary for rusting are:-
a.Presence of air
b. Presence of moisture.
What are Alloys ? How alloys are prepared? Discuss various types of alloys with suitable examples.
"An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal e.g. brass, bronze. Alnico etc.
An alloy is usually prepared by first melting the main metal and then dissolving the other elements in it in definite proportions. It is then cooled to room temperature,Alloys have been divided in to following three types.:-
1.Ferrous Alloys:- An alloy in which iron is present as one of the constituents is called as ferrous alloy.e.g. manganese steel (Fe = 86%, Mn = 13%C= 1%) and nickel steel (iron = 96 - 98% Ni = 4-2 %)
2.Non-Ferrous alloys:- An alloy which does not contain iron as a one of the constituents is called non-ferrous alloy, e.g. Brass (Cu = 80% 2n = 20 %) Bronze ( Cu = 90% Sn = 10%)
3.Amalgams:- An alloy containing mercury as one of the constituent metals is known as amalgam eg. sodiun amalgam ,zinc amalgam etc
Objectives, advantages, merits of alloy making?
Ans. Alloys are prepared to develop certain specific properties not possessed by constitment elements. The main objectives of alloy making are:-
1. To increase hardness, e.g, when carbon is added to iron, its hardness increases. This hardened iron is called steel.
2.To increase tensile strength. Chrome steel prepared by mixing iron and chromium has high tensile strength,
3. To increase resistance to corrosion stain less steel which is an alloy of iron chromium
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