Metals And Non-Metals

Metals and non-metals differ mainly in the way they gain or lose electrons.

Metals are elements that lose electrons and form positive ions. They are also called electropositive elements.

Atoms of metals usually have 1 to 3 electrons in their outermost shell.

Examples:

• Sodium: 11Na = 2, 8, 1
• Magnesium: 12Mg = 2, 8, 2
• Aluminium: 13Al = 2, 8, 3

Sodium loses one electron to form sodium ion:

Na → Na⁺ + e⁻

Magnesium loses two electrons to form magnesium ion:

Mg → Mg²⁺ + 2e⁻

Hydrogen and helium are important exceptions. Hydrogen has one electron and helium has two electrons in the outermost shell, but both are non-metals.

Physical Properties Of Metals

Metals show some common physical properties.

Lustre

Metals are lustrous and can be polished.

Iron, copper and aluminium show shiny surfaces when rubbed.

Gold, silver and copper show metallic lustre.

Examples:

• Aluminium – white
• Copper – reddish
• Gold – yellow
• Magnesium – white

Exception:

• Iodine is a non-metal but shows lustre.

Physical State

Metals are generally solids at room temperature.

Exceptions:

• Mercury
• Gallium

Malleability

Most metals can be beaten into thin sheets.

This property is called malleability.

Exception:

• Zinc is not malleable like common metals.

Gold and silver are among the most malleable metals.

Ductility

Metals can be drawn into thin wires.

This property is called ductility.

Melting And Boiling Points

Metals generally have high melting and boiling points.

Exceptions:

• Caesium
• Gallium

Density

Metals generally have high density.

Exception:

• Alkali metals have low density.

Important facts:

• Osmium has the highest density.
• Lithium has the lowest density.

Conductivity

Metals are good conductors of heat and electricity due to the presence of free electrons.

Important facts:

• Silver and copper are the best conductors.
• Lead, bismuth and mercury are poor conductors.

Hardness

Most metals are hard.

Exceptions:

• Sodium
• Potassium
• Lithium

Sonorous Nature

Metals produce sound when struck.

This property is called sonorous nature.

Alloy Formation

Metals form alloys.

An alloy is a homogeneous mixture of metals or a metal and a non-metal.

Chemical Properties Of Metals

Metals react with oxygen, water, acids, chlorine, hydrogen and salt solutions.

Reaction Of Metals With Oxygen

Metals generally react with oxygen to form metal oxides.

Metal + Oxygen → Metal oxide

Most metal oxides are basic in nature.

Some metal oxides are amphoteric.

Example:

• Aluminium oxide is amphoteric.

Reaction Of Metals With Water

Different metals react with water at different rates.

Sodium And Potassium

Sodium and potassium react vigorously with cold water.

They form metal hydroxide and hydrogen gas.

Calcium

Calcium reacts with water less violently.

Bubbles of hydrogen gas stick to the surface of calcium.

Magnesium

Magnesium does not react with cold water.

It reacts with hot water or steam.

Iron

Iron does not react with cold or hot water.

It reacts with steam to form iron oxide and hydrogen gas.

3Fe + 4H₂O → Fe₃O₄ + 4H₂

Reaction Of Metals With Acids

Metals generally react with dilute acids to form salt and hydrogen gas.

Metal + Acid → Salt + Hydrogen gas

Example:

Zn + 2HCl → ZnCl₂ + H₂

Copper does not react with dilute hydrochloric acid or dilute sulphuric acid.

Cu + dil. HCl → No reaction

Cu + dil. H₂SO₄ → No reaction

Metals generally do not react with nitric acid, except magnesium and manganese.

Nitric acid is a strong oxidising agent. It oxidises hydrogen into water instead of releasing hydrogen gas.

Aqua Regia

Aqua regia is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3:1.

Gold dissolves in aqua regia.

Reaction Of Metals With Chlorine

Metals react with chlorine to form metal chlorides.

Metal + Chlorine → Metal chloride

Examples:

2Na + Cl₂ → 2NaCl

Cu + Cl₂ → CuCl₂

Reaction Of Metals With Hydrogen

Metals react with hydrogen to form metal hydrides.

Metal + Hydrogen → Metal hydride

Examples:

Ca + H₂ → CaH₂

Calcium hydride is also called hydrolith.

Mg + H₂ → MgH₂

Reaction Of Metals With Salt Solutions

A more reactive metal can displace a less reactive metal from its salt solution.

General form:

Metal A + Salt solution of B → Salt solution of A + Metal B

Example:

CuSO₄ + Zn → ZnSO₄ + Cu

Here, zinc is more reactive than copper, so it displaces copper from copper sulphate solution.

But copper cannot displace zinc from zinc sulphate solution.

ZnSO₄ + Cu → No reaction

Non-Metals

Non-metals are elements that accept electrons to complete their octet.

They form negatively charged ions and are called electronegative elements.

Non-metals usually contain 4, 5, 6, 7 or 8 electrons in their outermost shell.

Example:

Nitrogen: Z = 7 = 2, 5

Nitrogen accepts three electrons to form nitride ion:

N + 3e⁻ → N³⁻

Physical Properties Of Non-Metals

Non-metals generally show properties opposite to metals.

• They are usually not lustrous.
• They are generally poor conductors of heat and electricity.
• They are not malleable.
• They are not ductile.
• They are usually brittle in solid state.

Important exceptions:

• Iodine is a non-metal but has lustre.
• Graphite is a non-metal but conducts electricity.
• Bromine is a non-metal and exists as a liquid.
• Sulphur and phosphorus are brittle non-metals.

Chemical Properties Of Non-Metals

Reaction Of Non-Metals With Oxygen

Non-metals such as carbon, sulphur and phosphorus react with oxygen to form non-metallic oxides.

These oxides are generally acidic in nature and turn blue litmus red.

Some oxides may be neutral.

Examples:

C + O₂ → CO₂

Carbon dioxide is acidic.

2C + O₂ → 2CO

Carbon monoxide is neutral.

S + O₂ → SO₂

Sulphur dioxide is acidic.

Reaction Of Non-Metals With Water

Non-metals do not react with water or steam to produce hydrogen gas.

Reaction Of Non-Metals With Acids

Hydrogen gas is not liberated when non-metals react with dilute acids.

Reaction Of Non-Metals With Hydrogen

Non-metals react with hydrogen to form compounds.

Examples:

2H₂ + O₂ → 2H₂O

H₂ + Cl₂ → 2HCl

N₂ + 3H₂ → 2NH₃

Reaction Of Non-Metals With Chlorine

Examples:

H₂ + Cl₂ → 2HCl

P₄ + 6Cl₂ → 4PCl₃

Reaction Of Non-Metals With Salt Solutions

A more reactive non-metal can displace a less reactive non-metal from its salt solution.

Example:

2NaBr + Cl₂ → 2NaCl + Br₂

Chlorine is more reactive than bromine.

But bromine cannot displace chlorine from sodium chloride.

2NaCl + Br₂ → No reaction

Ionic Or Electrovalent Compounds

When metals lose electrons and non-metals gain electrons, ions are formed.

The electrostatic attraction between oppositely charged ions forms an ionic compound or electrovalent compound.

Examples:

• NaCl
• KCl

Ionic compounds are generally:

• Solid
• High melting point compounds
• Soluble in water
• Insoluble in solvents such as kerosene and petrol
• Conductors of electricity in molten or aqueous solution state

They do not conduct electricity in solid state because ions are not free to move.

They conduct in molten or aqueous state because ions become free.

Reactivity Series Of Metals

The reactivity series is the arrangement of metals in decreasing order of reactivity.

Metals placed at the top of the series are most reactive.

A more reactive metal displaces a less reactive metal from its salt solution.

Example:

The order Mg > Zn > Cu > Ag shows that magnesium is most reactive and silver is least reactive among these.

Iron can displace copper from copper sulphate solution.

Metallurgy

Metallurgy is the process of extracting pure metals from their ores and refining them for use.

Occurrence Of Metals

Metals occur in the Earth’s crust in two main forms:

• Native state
• Combined state

Minerals

Minerals are elements or compounds that occur naturally in the Earth’s crust.

Native State

When metals are present in free or uncombined form, it is called native state.

Examples:

• Silver
• Copper
• Gold

Noble metals such as gold and silver occur in native state because they are not easily attacked by moisture, oxygen and carbon dioxide.

Combined State

When metals exist in the form of compounds, it is called combined state.

Ores

Ores are minerals that contain a high percentage of metal and from which the metal can be profitably extracted.

Important point:

• All ores are minerals, but all minerals are not ores.

Types Of Ores

Ores are mainly:

• Oxides
• Sulphides
• Carbonates
• Sulphates
• Halides

Important Ores

Ore	Formula	Metal
Bauxite	Al₂O₃·2H₂O	Al
Zincite	ZnO	Zn
Copper iron pyrites	CuFeS₂	Cu
Rock salt	NaCl	Na
Zinc blende	ZnS	Zn
Cinnabar	HgS	Hg
Magnesite	MgCO₃	Mg
Magnetite	Fe₃O₄	Fe
Epsom salt	MgSO₄·7H₂O	Mg
Galena	PbS	Pb
Horn silver	AgCl	Ag
Gypsum	CaSO₄·2H₂O	Ca
Pyrolusite	MnO₂	Mn
Limestone	CaCO₃	Ca
Haematite	Fe₂O₃	Fe
Carnallite	KCl·MgCl₂·6H₂O	Mg

Extraction Of Metals From Ores

The extraction of metals involves several steps.

Ores contain impurities such as:

• Sand
• Stone
• Clay
• Limestone
• Mica

These impurities are called gangue or matrix.

Steps In Metallurgical Process

The main steps are:

• Crushing and grinding of ore
• Enrichment or concentration of ore
• Extraction of metal
• Refining or purification of metal

Crushing And Grinding Of Ore

The ore is first broken into small pieces using crushers.

It is then converted into powder using:

• Ball mill
• Stamp mill

Enrichment Or Concentration Of Ore

Ore enrichment means removal of unwanted impurities or gangue from the ore.

Different methods are used for separating ore and gangue particles:

• Froth flotation process
• Hydraulic washing
• Magnetic separation
• Chemical methods

Extraction Of Metal

Before reduction, metal ores are often converted into their oxides.

This is because metal oxides are easier to reduce than metal sulphides and metal carbonates.

Roasting

Roasting is the process in which sulphide ores are converted into oxides by heating strongly in the presence of excess air.

Example:

2ZnS + 3O₂ → 2ZnO + 2SO₂

Calcination

Calcination is the process in which carbonate ores are converted into oxides by heating strongly in limited air.

Example:

ZnCO₃ → ZnO + CO₂

Reduction

Reduction is the process in which metal oxides are reduced to corresponding metals using a reducing agent such as carbon.

Refining Of Metals

Refining means purification of impure metal.

Electrolytic refining is used for refining impure metals.

Electrolytic Refining Of Copper

In electrolytic refining of copper:

• Crude copper is made the anode.
• A thin sheet of pure copper is made the cathode.
• Copper sulphate solution containing a small amount of dilute sulphuric acid is used as electrolyte.

On passing electric current, copper dissolves from the anode into the electrolyte.

Cu → Cu²⁺ + 2e⁻

This is oxidation.

An equal amount of pure copper from the electrolyte is deposited at the cathode.

Cu²⁺ + 2e⁻ → Cu

This is reduction.

Insoluble impurities settle at the bottom of the anode and are called anode mud.

Corrosion

Corrosion is the deterioration of the surface of metals.

It occurs when metals are exposed to moist air for a long time.

Rusting Of Iron

When iron is exposed to moisture for a long time, its surface deteriorates and forms a brown flaky substance called rust.

Reaction:

2Fe + xH₂O + O₂ → Fe₂O₃·xH₂O

Rust is hydrated ferric oxide.

Corrosion Of Copper

Copper reacts with moist carbon dioxide in air and forms a green coating of basic copper carbonate.

Reaction:

2Cu + CO₂ + H₂O → 2Cu(OH)CO₃

Tarnishing Of Silver

Silver becomes black when exposed to air because of formation of silver sulphide.

Reaction:

2Ag + S → Ag₂S

Prevention Of Corrosion

Corrosion can be prevented by:

• Coating the metal surface with paint, varnish or grease.
• Galvanisation.
• Alloying.

Galvanisation

Galvanisation is the process of protecting iron and steel by coating them with a thin layer of zinc.

It prevents rusting of iron.

Alloy

An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.

Steel

Steel is an alloy of iron and carbon.

The chapter mentions carbon content around 0.1-0.5% for steel.

Steel is:

• Hard
• Tough
• Strong

Uses:

• Rails
• Screws
• Girders
• Bridges
• Railway lines

Types Of Iron Based On Carbon Content

Type	Carbon Content
Steel	0.1-1.5% carbon
Wrought iron	Up to 0.5% carbon
Cast iron / Pig iron	2.0-4.5% carbon

Important points:

• Wrought iron is the purest form of iron.
• Pig iron is the least pure form of iron.

Alloy Steels

Alloy steels are formed by adding elements such as:

• Chromium
• Vanadium
• Titanium
• Molybdenum
• Manganese
• Cobalt
• Nickel

Important examples:

• Stainless steel – alloy of iron, chromium and nickel
• Manganese steel – about 86% Fe, 13% Mn and carbon; very hard and wear resistant
• Nickel steel – about 96-98% Fe and 2-4% Ni
• Chrome steel – mainly iron and chromium

Thermite Reaction

The chapter solution section gives the thermite reaction:

2Al + Fe₂O₃ → Al₂O₃ + 2Fe

The molten iron produced in this process is used to weld broken parts of heavy machinery.

This is called thermite welding.

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