4 Chem

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The Main Group Elements Of The Periodic Table

* ALKALI METALS

The elements of group 1-A

They are called alkali metals.

They include lithium (Li3) sodium (Na11) potassium (K19 ) -

Rubidium (Rb37) cesium (Cs55) and Francium (Fr87).

(10Ne)ns1

Sodium and potassium are abundant elements in The earth crust

Most important ore of sodium is Rock salt (NaCl)

The most important ore of potassium is KCl which is found in sea

water and in Carnelite deposits KCI. MgCl2. 6H2 O.

Other elements are rare.

Francium is a radioactive element produced from actinium

* General Properties of elements in the first group

(1) Presence of one electron in the outer energy level

So:

a) Each element is at the beginning of new period

b) The oxidation number is +1

c) Very active elements:

They have the lowest ionization potential

Second ionization potential is very large

(it needs to break a complete level)

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(2) Most of their compounds are ionic their properties depend on

(-ve) ion.

-They have the lowest melting and boiling points.

-They are the most malleable.

(3) They have the largest atomic radius So:

a) The highest electropositivity

b) Some of them are used in photo-electric cells (K,Cs)

c) They have low densities.

d) They form strong ionic bond.

(4) The excited electron gives characteristic colour used in dry test.

e.g LiCrimson.

NaGolden yellow

K Pale violet.

CsBluish violet.

(5) They are kept away from air and humidity (under Kerosene)

* (6) Chemical properties

1- Action of atmospheric air

They lose their metallic luster forming oxides.

Lithium can react with nitrogen.


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2- With water

forming hydroxide and hydrogen gas.

This accompanied by large amount of heat energy enough to burn

hydrogen

( explosion occurs with Cs )

(we cant extinguish burning of sodium with water)

3- With oxygen

The type of oxide is differ according to the kind of the element

NOTE

KO2 reacts with CO2 giving O2 soit is used in closed area to purify the

air

The normal oxide is X2O

Oxide can be prepared by dissolving metal in ammonium solution

then adding the calculated amount of oxygen.

4- With acids vigorous reaction causes explosion


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5- With hydrogen

If sodium hydride is fused electrolyzed H2 evolves at anode .

Hydrides are reducing agent (react with water giving hydrogen).

6- With halogens

React vigorously forming very stable ionic halides

7- With non-metals

- Hot alkali metals react directly with S , P

8- action of heat on alkali metal Oxygenated saltsThey are thermally stable

a) Metal carbonates dont decompose except Li2CO3

(decomposed at 1000 0c)

b) Metal nitrate decomposes given metal nitrite and oxygen

Note

KNO3 is used in bombes - while NaNO3 is deliquescent (absorbs

water) from air So, it doesnt used in bombes.


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* Extraction of Metals

These elements are the most powerful reducing agents . They don t

found in an uncombined state.To prepare free metal an electron must be restored to the positive ion

(using electrolysis)

Preparation : Electrolysis of fused halide in presence of flux


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* Group 5A

Elements

- Nitrogen N , phosphorus P , Arsenic As , Antimony Sb , Bismuth Bi.

Presence

Nitrogen = 80% of atmospheric air

Phosphorus = The 9th element in the earth crust

It is found as Ca3(PO4)2 - apatite CaF2.Ca3(PO4)2

Arsenic - antimony and bismuth are found in the form of sulphide As2 S3

-Sb2 S3 - Bi2 S3

* general Properties

(1) Element Structure

N7 = [He2] , 2S2

, 2P3

P15 = [Ne10]3S2

, 3P3

As33 = [Ar18]4S2

, 3d10 , 4P3

Sb51 = [Kr36]5S2

, 4d10

, 5P3

Bi83 = [Xe54]6S2

, 4F14

, 5d10

, 6P3

(2) Non- Metallic properties

The metallic properties increase with increasing of atomic number.

Nitrogen and phosphorus are non - metals .

Arsenic and antimony are metalloids.

Bismuth is metal.


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(3) The Molecule

Nitrogen molecule contains two atoms N2 .

The vapour of P - As and Sb contain four atoms

( P4 - As4 - Sb4 )

The vapour of Bismuth in high temp.is diatomic Bi2

(4) Oxidation number

They have several oxidation number from -3 to +5

Their positive oxidation number are found in oxides.

(5) With oxygen


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forming oxides some of them are acidic, some are amphoteric - or basic

-The basic property increases and the acidic property decrease with

increasing of atomic number.

(6)With hydrogen

- The oxidation number of most their hydrides = -3

- Ex

Ammonia NH3 phosphine PH3 Arsine AsH3

- The central atom has one pair of electrons , So they can form coordinate

bond.

- Ex


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-The polarity and solubility are decreased by increasing atomic no.

-Thermally unstable - They are decomposed by gentle heating.

(7)Allotropy

- The presence of the element in more than one form, of different physical

properties, but of similar chemical ones

-This is due to the presence of the element in different crystalline

forms(number and arrangement of atoms).

N.B.

Nitrogen and bismoth have no allotropic form


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* Nitrogen

* Properties

1- with hydrogyn

by electric spark forming ammonia gas .

2-with Oxygen

By electric arc (3OOOOC) forming nitric oxide

Nitric oxide changing into nitrogen dioxide in air

3-with metals

In high temperature forming metal nitride

magnesium nitride decomposes in water

4- with calcium carbide

Calcium Cyanamid is usedas a fertilizer.

Important nitrogen comod


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* AMMONIA

* Preparation

I) In lab


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Ammonia gas is collected by downward displacement of air.

II) In industry: (Habers Method)

From hydrogen and nitrogen in presence of catalyst (Iron) -200 atmospheric

pressure and 500OC.


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* NITRIC ACID

* Preparation

I)In lab

Put potassium nitrate and conc. H2SO4 in retort - heat (less than 100Oc)

then collect nitric acid in receiver

* Properties

1.Action of heat

2.

Oxidizing agent

3. With metals

a)Metals above hydrogenin electrochemical series Produced metal


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nitrate and hydrogen which reduces the acid

b) Metals below hydrogen: The metal is oxidized by the acid to metal oxide- then metal oxide reacts with acid

4. Some metals

e.g.Iron Fe , chromium Cr and aluminum Al are not affected by conc.

acid due to passivity

Passivity

A layer of metal oxide surrounds the metal.

It is non porous so it protects the metal from further reaction.

* Economic importance

.NitrogenManufacture of ammonia - nitric acid and fertilizers.

.Phosphorus

Manufacture of matches - rat poison - fertilizers and incendiary bombs .

Many alloys such as bronze (Cu + Sn + P)

3. Antimony

In making accumulators (with lead)

- Sb2 S3 in dying

4. moys of Bismuth

with Pb , Cd and tin forming easy melting alloys .


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