Metals and Non-metals. Comparison of physical properties of metals and non metals

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Sheeba Musthafa Page 1

Metals and Non-metals

Comparison of physical properties of metals and non metals

PHYSICAL PROPERTY METALS NON-METALS

Physical State Mostly solids

(Liquid -mercury)

Mostly solids or gases (Liquid -bromine) Metallic lustre

(having a shining surface)

Lustrous Dull

(Iodine -lustrous)

Density High Low

Melting Point &boiling point High

(Gallium, Caesium, Li, Na, K–

low)

Low

(Carbon: diamond – high)

Hardness Hard

(Alkali metals- Li, Na, K- soft)

Soft

(Diamond- hardest) Malleability (ability to be beaten into

thin sheets)

Malleable

Best- gold & silver

Non-malleable

Ductility (ability to be drawn into thin wires)

Ductile Best- Gold

Non-ductile

Sonority (ability to produce a ringing sound on striking a hard surface)

Sonorous Non-sonorous

Heat Conductivity Very good conductors of heat Best- silver & copper

Poor conductors of heat

Electrical Conductivity Very good conductors of electricity

Poor conductors of electricity (Graphite- good conductor)

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Sheeba Musthafa Page 2 COMPARISON OF CHEMICAL PROPERTIES OF METALS AND NON METALS

Chemical properties of Metals

1. Reactive Metal + Oxygen → Metal Oxides (Basic)

↓

Bases / Alkalis

(Turns Red litmus Blue) 2. Reaction of metals with Water

Metal + Water → Metal Oxides + Hydrogen

(Bases)

3. Reactive metals + dilute acids → salt of the metal + Hydrogen 4. Reactive metal A + Salt solution of B → Salt solution of A + Metal B

(Metal A is more reactive than metal B) Important !!!

 The thin protective oxide coating on the surface of Mg, Al, Zn, Pb prevent the metal from further oxidation.



 Anodising is a process of forming a thick oxide layer of Aluminium. During anodizing, a clean Al article is made the anode and is electrolyzed using dilute H2SO4. Oxygen gas produced at the anode reacts with Al and forms protective thick oxide layer. It helps to resist corrosion and gives the Al articles an attractive finish.

 Amphoteric oxides are metal oxides that react with both acids and bases to produce salt and water. Eg: Aluminium oxide, Zinc oxide

PROPERTY METALS NON-METALS

Chemical nature Electropositive

(tendency to lose electrons)

Electronegative

(tendency to gain electrons) Action with Oxygen Forms basic metallic oxides Forms acidic non-metallic oxides

Action with acids Reactive metals liberate H2 gas Does not liberate Hydrogen gas

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Sheeba Musthafa Page 3 Eg: Al2O3 + 6 HCl → 2 AlCl3 + 3 H2O

Al2O3 + 2 NaOH → 2 NaAlO2 + H2O

 Iron does not burn on heating, but iron filings burn vigorously when sprinkled in the flame of the burner.

 Copper does not burn on heating, but gets covered with a black coloured layer of CuO.

 Reaction of K & Na with water is exothermic that the evolved H2 immediately catches fire.

 Ca & Mg floats on the surface of water due to the bubbles of Hydrogen sticking to its surface.

 Nitric acid being a strong oxidizing agent, does not give hydrogen gas with metals. It oxidises H2 to H2O and gets reduced to any of the nitrogen oxides (N2O, NO, NO2).

Reactivity / activity series

The series showing the arrangement of metal in the decreasing order of their activity. Any metal in the series is less reactive than its preceding metals

.

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• Stability of elements

• Noble gases have a completely filled valence shell and are hence stable.

• Octet electronic configuration similar to noble gases is found to be stable.

• The elements differ in their reactivity due to their tendency to attain a completely filled valence shell.

 How do metals and non-metals react?

Metals Non-metals

 Metals have 1, 2 or 3 valence electrons

 Metals show a tendency to lose electrons from their valence shell.

 Metals are electropositive

 Non-metals have 5, 6 or 7 valence electrons

 Non-metals show a tendency to gain electrons to their valence shell.

 Non-metals are electronegative

Eg: Formation of Sodium chloride

Ionic or electrovalent bond.

 The chemical bond formed by the transfer of electrons from the valence shell of a metal to the valence shell of a non-metal, thereby both elements acquiring nearest noble gas configuration is called ionic or electrovalent bond.

 An ionic bond is formed between metals and non-metals.

 The compounds formed through ionic bonding are called ionic compounds or electrovalent compounds. eg NaCl , CaO, MgO, MgCl2, ZnCl2 etc

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 Properties of ionic compounds

1. Ionic compounds are generally hard, brittle crystalline solids (due to strong electrostatic force of attraction).

2. Ionic compounds have high melting and boiling points (due to strong inter-ionic attraction).

3. Ionic compounds are soluble in polar solvents like water and insoluble in non- polar solvents like kerosene and petrol.

4. Ionic compounds in the solid state do not conduct electricity. They conduct electricity only in the molten state or in aqueous solutions due to the availability of mobile charged ions.

 Occurrence of metals

 The metals at the bottom of the reactivity series are least reactive and are found in the elemental form. Example:- Au, Ag, Pt, Cu.

 Most metals are found in the form of compounds as oxides, sulphides, carbonates etc.

1. Minerals: Elements or compounds found naturally in the earth’s crust.

2. Ores: The minerals from which metals can be extracted profitably.

3. Gangue: The earthly impurities present in the ore particles.

4. Flux: The substance used to remove the gangue.

5. Slag: The molten fusible substance formed when flux reacts with gangue.

6. Metallurgy: Several steps involved in the extraction of pure metal from its ores.

 Steps involved in extraction of metals:

1. Enrichment of ore

2. Extraction of metal from the enriched ore 3. Refining of metals

 1. Enrichment / Concentration of the ore

o The process of removing gangue from the ores.

o Physical or chemical properties of the gangue and the ore decide the method employed for concentration of the ore. Eg: hydraulic washing, froth floatation process, magnetic separation.

 How are metals classified based on their reactivity?

1. Metals of high reactivity K, Na, Ca, Mg, Al 2. Metals of medium reactivity Zn, Fe, Pb, Cu

3. Metals of low reactivity. Ag, Au

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

2.

Extraction of metal from the enriched ore

Steps involved in extraction of metals

 (a) Extracting metals low in the reactivity series (Hg, Cu):

Ores can be reduced to metal by heating alone.

Eg : Mercury from its ore Cinnabar (HgS) a. Conversion of sulphide to oxide

2HgS(s) + 3O₂ (g) ^heat→ 2HgO(s) + 2SO₂ (g) b. Decomposition of oxide to metal

2HgO(s) ^heat→ 2Hg(l) + O2(g)

 (b) Extracting Metals in the middle of the reactivity series (Fe, Zn, Pb):

 Step 1. The metal sulphides and carbonates are converted to metal oxides, by roasting or calcination.

 Step 2.The metal oxides are then reduced to the corresponding metals by using suitable reducing agents like carbon or highly reactive metals like Al.

Step 1

 Roasting

a. Used to convert sulphide ores into oxides.

b. Done by heating the sulphide ore strongly in the presence of excess air, so that oxygen gets added to form the corresponding oxides.

c. Sulphur impurities escape as SO₂ gas.

 Calcination

a. Used to convert carbonate ores to oxides.

b. Done by heating the carbonate ore to a high temperature in the absence of air.

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Sheeba Musthafa Page 7 Step 2. Reduction of metallic oxides to metals

 The oxide obtained by calcination or roasting is then reduced to the metal using a reducing agent (carbon or highly reactive metals like Al)

 Metal oxide + reducing agent → Metal + oxidized reducing agent

2 ZnO (s) + C (s) ^Heat→ 2 Zn (s) + CO2 (g) Fe2O3 (s) + 2 Al (s) ^Heat→ 2Fe (l) + Al2O3(s)

 (c) Extraction of metals towards top of the reactivity series

 Metals high in the reactivity series are very reactive and cannot be obtained from their compounds by heating with carbon. These metals have more affinity for oxygen than carbon.

 These metals are obtained from their compounds by electrolytic reduction.

 Sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides.

 3. Refining of metals

Electrolytic refining - Refining by electrolysis.

 A thick block of the impure metal is made anode.

 A thin strip of the pure metal is made cathode.

 A water soluble salt of the metal to be refined is taken as electrolyte.

 Corrosion

 The process of slow wasting away of metal by the action of atmospheric gases and moisture is called corrosion.

 Silver objects : Black deposit (Silver sulphide)

 Copper objects : Green deposit (Basic copper carbonate)

 Iron objects : Brown flaky deposit (Hydrated ferric oxide)

 Conditions necessary for corrosion of iron

 Rusting agents

 Air (oxygen)

 Moisture (water).

 Prevention of corrosion

 Painting

 Applying grease or oil

 Galvanizing

 Chrome plating

 Anodising:

 Alloying

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 Alloy

 Homogeneous mixture of two or more metals or a metal with a non-metal.

 It is prepared by first melting the primary metal and then dissolving the other elements in it in definite proportions. It is then cooled to room temperature.

 Why do we make alloys?

For altering the properties of metals like:

 Increasing hardness: Adding carbon to iron.

 Making corrosion resistant: Adding Ni and Cr to iron (stainless steel)

 Lowering melting point: Mixing tin + lead (solder )

 Reducing electrical conductivity: Mixing Cu and Zn to make Brass

 Reducing reactivity: Adding mercury to sodium.

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