ICSE Class 10 Chemistry Chapter 07 Metallurgy

Chapter 7: Metallurgy

Important Points To Remember

The elements which are having 1, 2 or 3 valence electrons, can be drawn into wires, beaten into sheets, are lustrous and good conductors of heat and electricity are called as metals. Metals are electron donors and can form positively charged particles called cations. For example: Metals lose valence electrons to achieve stable configuration and thus they form positively charged particle known as cations.

Na - e- gives Na+ with electron configuration 2, 8 from 2, 8, 1

K - e- gives K+ with electron configuration 2, 8, 8 from 2, 8, 8, 1

Mg - 2e- gives Mg2+ with electron configuration 2, 8 from 2, 8, 2

Ca - 2e- gives Ca2+ with electron configuration 2, 8, 8 from 2, 8, 8, 2

Al - 3e- gives Al3+ with electron configuration 2, 8 from 2, 8, 3

Metals like Gold, Copper, Platinum, etc., occur in free state or native state as they are unreactive in nature.

The elements which are having 5, 6 or 7 valence electrons and cannot be drawn into wires or beaten into sheets, are non-lustrous and poor conductors of heat and electricity are called as non-metals. Non-metals are electron acceptors and can form negatively charged particles called anions. For example: Non-metals gain electrons to complete their octet and get converted to negatively charged particle known as anions.

F + e- gives F-1 with electron configuration 2, 8 from 2, 7

O + 2e- gives O-2 with electron configuration 2, 8 from 2, 6

N + 3e- gives N-3 with electron configuration 2, 8 from 2, 5

Cl + e- gives Cl- with electron configuration 2, 8, 8 from 2, 8, 7

S + 2e- gives S-2 with electron configuration 2, 8, 8 from 2, 8, 6

In the periodic table the metals are present in groups 1 and 2 (highly electropositive elements). Transition elements in the middle of the periodic table are metals. The metallic character (tendency to lose electrons) increases as we move down the group therefore metals are also present at the bottom of every group in the periodic table.

Elements of group IA are called as alkali metal. The members of this group are Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs) and Francium (Fr).

Reaction Of Alkali Metals With Air

Lithium, sodium and potassium react with oxygen at normal temperature to form their respective oxides.

4Li + O2 gives 2Li2O

4Na + O2 gives 2Na2O

4K + O2 gives 2K2O

Lithium reacts with nitrogen to form lithium nitride.

6Li + N2 gives 2Li3N

Reaction Of Alkali Metals With Water

These metals on reaction with cold water form soluble bases called as alkali.

2M + 2H2O gives 2MOH + H2 (general equation)

where M can be Li, Na, K etc.

2Li + 2H2O gives 2LiOH + H2

2Na + 2H2O gives 2NaOH + H2

2K + 2H2O gives 2KOH + H2

2Rb + 2H2O gives 2RbOH + H2

Reaction Of Alkali Metals With Acids

Sodium and potassium reacts with dil. HCl explosively to liberate Hydrogen gas.

2Na + 2HCl(dil.) gives 2NaCl + H2 with arrow pointing up

2K + 2HCl(dil.) gives 2KCl + H2 with arrow pointing up

All elements of this group have one electron in their valence shell hence, their valency is +1.

General Characteristics Of Alkali Metals

They are highly reactive elements and does not occur in free state.

They have one electron in their valence shell. Thus, they loose electrons and get converted to unpositive ions cation. These elements have lowest ionization energy in their respective periods thus, they easily loose electrons and get converted to cation.

M - e- gives M+ (general equation)

Li - e- gives Li+ with electron configuration (2, 1)

Na - e- gives Na+ with electron configuration (2, 8, 1)

K - e- gives K+ with electron configuration (2, 8, 8, 1)

They are stored under kerosene because they easily react with oxygen and water vapour to form their oxides and hydroxides. The reactivity increases on moving down the group.

Alkali metals have low melting point and boiling point.

They can be easily cut with the help of knife. Freshly cut metal imparts a silvery appearance, but after sometime the metal gets tarnished due to the formation of oxide layer.

Alkali metals being highly electropositive elements undergo ionic bond formation with non-metals.

For example: Formation of sodium chloride is by the ionic bond.

Na with electron configuration 2, 8, 1 loses one electron to Cl with electron configuration 2, 8, 7

Na - e- gives Na+ and Cl- + e- gives Cl-

This forms Na+ and Cl- with dotted line between them representing ionic bond

Alkali metals are strong reducing agents.

Alkali metals react with cold water to form their respective hydroxides with the liberation of hydrogen. The reaction of alkali metals with cold water is highly vigorous, exothermic and proceeds with explosion.

Alkali metals displace hydrogen on reaction with dilute acids. However, this reaction is highly vigorous and exothermic.

Alkali metals are obtained by the electrolysis of their fused or molten chlorides.

NaCl gives Na+ + Cl-

At Cathode: Na + e- gives Na+

At Anode: Cl- + e- gives Cl-1

Alkali metals are obtained at cathode during electrolysis.

Elements Of Group IIA

Elements of group IIA are called as alkaline earth metals. The members of this group are Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium (Ra).

Teacher's Note

Alkali metals are so reactive that they must be stored in special conditions - this is why your chemistry lab has strict storage procedures, just like how food in your kitchen needs proper storage to stay fresh.

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