ICSE Class 10 Chemistry Chapter 07 Metallurgy

7 Metallurgy

Syllabus

(i) Definition of Metals and Non-metals. Self-explanatory.

(ii) Position of the metals (Alkali metals and alkaline earth metals) in the Periodic Table and general characteristics applied to these elements with reference to the following - occurrence, nature, bonding, action of air, action of water, action of acids. Self-explanatory.

(iii) Comparison of Metals and Non-metals. General properties with special reference to physical properties: state, lustre, melting point, density, ductility, malleability, brittleness, conduction of electricity (exceptions to be specifically noted - e.g. graphite, mercury); chemical properties: a metal forms at least one basic oxide; non-metal, an acidic or neutral oxide; discharge of metallic ions at the cathode from fused metallic chlorides (link with bonding and ion formation); many metals liberate hydrogen from dilute HCl and H2SO4.

In the physical properties of metals and non-metals, atomicity and valence electrons should also be included; suitable examples must be given for basic, acidic and neutral oxides; formation and discharge of ions at the cathode (metallic) and anode (non-metallic) should be explained with examples.

(iv) Reduction of metallic oxides; some can be reduced by hydrogen, carbon and carbon monoxide (e.g. copper oxide, lead oxide, iron (II) oxide and some cannot (e.g. Al, MgO - refer to activity series). Equations with conditions and observations should be given.

(v) Extraction of metals based on the activity series. Extraction of metals: Principle of extraction of metal from its compounds by reduction - carbon reduction, electrolytic reduction. Active metals by electrolysis e.g. sodium, aluminium (reference only).

(iv) Corrosion of iron and its prevention Experiment to illustrate that moisture and oxygen in air are responsible for the corrosion : Reaction of corrosion, Prevention by painting and galvanization.

(vii) Metals and their alloys : common ores of iron, aluminium and zinc. Extraction of Aluminium; Metals and their alloys : Occurrence of metals in nature - mineral and ore. Common ores of iron, aluminium and zinc. Dressing of the ore - hydrolic method, magnetic separation, froth flotation method, chemical method by using chemical - NaOH for purifying bauxite - Baeyer's process.

Extraction of Aluminium : the constituents in the charge, method of electrolytic extraction (flow chart to be used); structure of electrolytic cell and reason for using cryolite, electrolyte, electrodes, electrode reaction.

Description of the changes occurring, purpose of the substances used and the main reactions with their equations.

(a) Uses of iron, aluminium and zinc and their alloys. Uses of iron, aluminium and zinc and their alloys. Composition of their alloys - steel, duralamin, brass.

(b) Other important alloys - bronze, fuse metal and solder. Uses only

7A. Metals And Non-Metals

7.1 Introduction

There are 118 different elements known to us today. These elements are widely distributed in earths crust in free state as well as in the combined form.

Approximate relative abundance of some elements in the earth crust are:

These elements have been classified into metals and non-metals based on their properties. Of these known elements, only 22 are non-metals.

All the metallic elements (except mercury) are solids whereas 11 non-metals are gases, one is a liquid (bromine) and the remaining non-metals are solids.

7.2 Metals

The knowledge of metals is very old. Copper was the first metal to be used by man for making utensils, weapons and for other purposes.

Gold, silver, copper, lead, iron, tin, antimony and mercury (earlier named quick silver) have been known to mankind from the ancient times.

Metals are widely used in our daily life for a large number of purposes. Some of the metals are used in making jewellery and coins; some are employed in making utensils and furniture, and some in the construction of heavy machinery, tools, transport vehicles and many in the manufacturing of other equipments. Metals often find applications as catalysts in various industrial processes such as hydrogenation of vegetable oils, manufacture of ammonia, sulphuric acid, nitric acid, dyes, drugs, etc. Metals, though in small quantities, have also been recognized as essentials for various biological processes. For example, iron is a constituent of blood pigment and magnesium of plant pigment.

Metals are defined as the elements which form positive ions by the loss of electrons. For example: Sodium, magnesium and aluminium are metals because they form positive ions by the loss of 1, 2 and 3 electrons respectively.

Na - e- \(\rightarrow\) Na+

Ca - 2e- \(\rightarrow\) Ca2+

Al - 3e- \(\rightarrow\) Al3+

Note : Hydrogen is a non metal, which forms positive ion.

H - e- \(\rightarrow\) H+

Non-metals are the elements which form negative ions by the gain of electrons. For example : Chlorine, oxygen and nitrogen are non-metals because they form negative ions by gain of 1, 2 and 3 electrons respectively.

Cl + e- \(\rightarrow\) Cl-

O + 2e- \(\rightarrow\) O2-

N + 3e- \(\rightarrow\) N3-

The number of electrons lost or gained by an element is equal to its valency.

Metals constitute the mineral wealth of a country. The major metals in the earth's crust in the decreasing order of their abundance are aluminium, iron, calcium, sodium, potassium and magnesium. The major non-metals in the earth's crust in the decreasing order of their abundance are oxygen, silicon, phosphorus and sulphur.

7.3 Non-Metals

Non-metals though small in numbers play a very vital role in our daily life.

Hydrogen, the lightest element known, is used in the hydrogenation of vegetable oils to make ghee, as a fuel and in the manufacture of compounds. It is also the essential part of organic compounds. Proteins, fats, carbohydrates, enzymes, vitamins, etc., are all compounds of carbon, and are essential for the growth and development of living organisms. The presence of oxygen gas in air is essential for respiration, and for combustion. Nitrogen is the most abundant element present in the atmosphere. Its presence in air reduces the rate of combustion. Due to its inertness, it is also used to preserve food. Life would not have been possible in the absence of non-metals like carbon, oxygen, nitrogen and hydrogen.

7.4 Categorisation Of Metals

The metals have been categorised on the basis of their characteristics as given below.

7.4.1 Alkali Metals

The elements such as lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr) have one electron in their outermost orbit and show one valency. So they are placed in IA group (the first column on the left) of the Periodic Table. They are known as alkali metals, as they react with water to form their hydroxides which are strong alkalies.

2M + 2H2O \(\rightarrow\) 2MOH + H2 (Alkali)

Where M is any metal of IA group.

Hydrogen is placed in this group as it has one electron, but it is not an alkali metal.

Characteristics

1. Occurrence : All of them are very reactive and do not occur in free state.

2. Nature : They are soft (can be cut with a knife) and have low melting and boiling points.

3. Bonding : All alkali metal salts (except some salts of lithium) are ionic in nature.

4. Action of air : They react rapidly with oxygen and water vapour in the air. Reactivity of these metals increases down the group.

5. Action of water : They react violently with water and produce hydrogen.

2M + 2H2O \(\rightarrow\) 2MOH + H2

(Any Alkali metal)

6. Action of acids : They react violently with dil HCl and dil. H2SO4, to produce hydrogen

2M + 2HCl \(\rightarrow\) 2MCl + H2

(Any Alkali metal)

7. They have low ionisation energy and form unipositives ion easily.

M(g) - e- \(\rightarrow\) M1+(g)

They are strong reducing agents.

8. When freshly cut, they show typical silvery white metallic lustre but soon they turn dull (tarnish) because of their reaction with air.

9. All alkali metal salts impart colour to the flame, e.g., lithium (crimson red), sodium (golden yellow), potassium (pale violet).

10. Alkali metals are obtained by electrolysis of their molten salts.

7.4.2 Alkaline Earth Metals

The elements such as beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra) are known as alkaline earth metals, because their oxides occur in the earth's crust and their hydroxides are alkalies.

All the elements of this group have two electrons in their outermost orbit and show the valency two, so they are placed in IIA group of the Periodic Table.

Characteristics

1. Occurrence : They are reactive metals (less reactive than alkali metals); hence they do not occur in free state in nature.

2. Nature : They are greyish white in colour and harder than the alkali metals.

3. Bonding : All the alkaline earth metal salts except beryllium are ionic compounds.

4. Action of air : They are less reactive than alkali metals.

Their reactivity increases on moving down the group.

5. Action of water : They react with water to produce hydrogen.

M + 2H2O \(\rightarrow\) M(OH)2 + H2

(Any alkaline metal) (Alkali)

6. Action of acids : They react with dil HCl and dil H2SO4 to produce hydrogen.

M + 2HCl \(\rightarrow\) MCl2 + H2

M + H2SO4 \(\rightarrow\) MSO4 + H2

7. They have low ionisation energy (higher than alkali metals) and form dipositive ion.

M - 2e- \(\rightarrow\) M2+

They are also strong reducing agents.

8. Melting points and boiling points are comparatively low but these are higher than the alkali metals.

9. Except beryllium and magnesium, all other alkaline earth metals impart colour to the flame like calcium-brick red, strontium-crimson, barium-apple green and radium-crimson.

10. They are obtained by electrolysis of their molten salts.

7.4.3 Transition metals

They are placed in the middle of the Periodic Table (group 3 to group 12). Their two outermost

- Not in syllabus

Teacher's Note

The periodic table helps us understand why sodium reacts more vigorously with water than magnesium - a key observation when cleaning laboratory equipment or handling industrial chemicals safely.

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