The document discusses hydrogen as the first element in the periodic table, highlighting its properties, methods of preparation, and chemical behavior. It covers hydrogen's role in forming dihydrogen, water's chemical properties, and various removal techniques for hardness in water. Additionally, the document mentions hydrogen peroxide, its preparation, uses, and the significance of heavy water in nuclear reactors.

2. INTRODUCTION
 Hydrogen, chemical element that exists as a gas at room temperature.
When hydrogen gas burns in air, it forms water.
 Hydrogen has the smallest atoms of any element. A hydrogen atom contains
one proton, and only one electron . The proton is the center, or nucleus, of
the hydrogen atom, and the electron travels around the nucleus.
 Pure hydrogen exists as hydrogen gas, in which pairs of hydrogen atoms
bond together to make molecules.
 First element in the periodic table with atomic mass of 1 u and atomic
number 1.

3. Discovery of Hydrogen
In 1766, Henry Cavendish was the first to
recognize hydrogen gas as a discrete substance,
by identifying the gas from a metal-acid reaction
as flammable air. In 1781 he was the first person
to find that the gas produces water when burned.
This was a key experiment in disproving the
Aristotelian theory of the four elements.

4. THE STRUCTURE OF HYDROGEN
ATOM
The hydrogen atom
consisting the
proton in the
centre or the
nucleus of the
hydrogen atom and
the electron

6. POSITION OF HYDROGEN IN THE PERIODIC TABLE

7. RESEMBLANCE WITH
OTHER ELEMENTS
• With Alkali Metals:
Hydrogen has an electronic configuration of 1s1 which is similar to the
electronic configuration of alkali metals (ns1). Hydrogen forms oxides, halides
and sulphides like alkali metals. But it gains an electron to become an anion. It
has high ionization enthalpy and forms covalent bonds.
• With Halogens:
In terms of ionization enthalpy, hydrogen resembles halogens. Like halogens,
hydrogen forms diatomic molecule, combines with elements to form hydrides and
a large number of covalent compounds. But it loses an electron to become a cation
and hydrogen reacts with halogens themselves.

8. Preparation of Dihydrogen
There are a number of methods for preparing dihydrogen from metals and
metal hydrides:

9.  It is usually prepared by the reaction of granulated zinc with the dilute
hydrochloric acid.
Zn + 2H+ Zn+2+ H2
 It can also be prepared by the reaction of zinc with aqueous alkali.
Zn + 2NaOH Na2ZnO2 + H2

10. COMMERCIAL PRODUCTION
• 1- Electrolysis of acidified water using platinum electrode gives
HYDROGEN.
• 2H2O ELECTROLYSIS 2H2 + O2
• 2- Electrolysis of warm aqueous barium oxide solution between
nickel electrodes.
• 3- In manufacture of sodium hydroxide and chlorine by electrolysis
of brine solution (Byproduct)
• 4- Reaction of steam on hydrocarbons or coke at high
temperatures in prescence of catalyst gives hydrogen.
• Eg. CH4 + H2O CO+ 3H2
1270K/
Ni

12. PHYSICAL PROPERTIES
• DIHYDROGEN IS COLOURLESS, ODOURLESS AND TASTELESS.
• IT IS COMBUSTIBLE. HYDROGEN AND HELIUM IS PRESENT ON THE SURFACE OF
THE EARTH.

13. CHEMICAL PROPERTIES
 The chemical behavior of dihydrogen, like all other molecules depends
the bond dissociation enthalpy.
 The inertness of dihydrogen at room temperature is due to the
dissociation enthalpy
 Since it’s orbital 1s is empty, it combines with almost all elements
 It can lose 1 electron to form H+, gain one electron to form H- or share
it’s electron to form single bonds

14. Reactions of Hydrogen with other
substances
Reactions with substance also gives us the
chemical properties of hydrogen:
• Reaction with Halogen: It leads to the formation of Hydrogen Halides
H2 (g) + X2 (g) 2HX (g)
In which X is a halogen, eg. F, Cl, Br, I.

15.  Reaction with Dioxygen: It reacts with dioxygen to form water. The reaction is
highly exothermic
2H2 + O2 2H2O

16.  Reaction with Dinitrogen:
With Nitrogen it forms Ammonia
3H2 + N2 2NH3
 Reaction With Metals:
It combines with many metals at a high temperature to yield the corresponding hydrides.
H2 + 2M 2MH (M=ALKALI METAL)
 Reaction with metal ions and metal oxides:
It reduces some metal ions in aqueous state.
H2(g) + Pd2+ (aq Pd(s) + 2H+(aq)
It reduces oxides of metals into their corresponding oxide:
yH2(g) + MxOy (s) xM(s) + yH2O(L)

18. Uses Of Dihydrogen

20. WATER

21. • Major part of the living beings is made up of water
• Humans have 65% of water while some plants have 95% of water
• It is a solvent of great importance and necessary for the survival of all
organisms
• The distribution of water around the globe is not uniform

22. CHEMICAL
PROPERTIES OF
WATERWater reacts with a number of substances

23. Amphoteric Nature
Water has the ability to act as an acid as well as a base
H2O + NH3 (OH-) +NH4+
H2O + H2S (H3O+) + HS+

24. Redox Reaction
Water can be easily reduced to dihydrogen by highly electropositive metals
2H2O + 2Na 2NaOH + H2
Water is oxidized to O2 during photosynthesis
6CO2 +12H2O C6H12O6 + 6H2O +6O2

25. Hydrolysis Reaction and Hydrates Formation
• Due to high dielectric constant, water has a very hydrating tendency. It
dissolves many tonic compounds. However, certain covalent and some
ionic compounds are hydrolysed in water.
P4O10 + 6H2O 4H3PO4
• From aqueous solution many salts can be crystallized as hydrated
salts. These are of different types: (i)coordinate water (ii) interstitial
water (iii) hydrogen bonded water

26. • Water which contain salts of magnesium and calcium in
the form of hydrogen carbonate, chloride and sulphate is
called HARD WATER. It does not give lather with soap
• Water free from soluble salts of calcium and magnesium
is known as SOFT WATER. It gives lather with soap
easily.

27. Hard Water
The hardness of water is of two types:
 Temporary Hardness
 Permanent Hardness

28. REMOVAL OF TEMPORARY HARDNESS
DUE TO MAGNESIUM AND CALCIUM HYDROGEN
CARBONATES
 BOILING: DURING BOILING, THE SOLUBLE MG(HCO3)2 IS CONVERTED
INTO INSOLUBLE MG(OH)2 AND CA(HCO3)2 IS CHANGED TO
INSOLUBLE CACO3. THESE PRECIPITATES CAN BE REMOVED BY
FILTRATION. FILTRATE THUS OBTAINED IS A HARD WATER.
MG(HCO3)2 MG(OH)2 +
2CO2
CA(HCO3)2 CACO3 + H2O
+ CO2
 Clarke’s Method: A calculated amount of lime is added to hard water
which precipitates out calcium carbonate and magnesium hydroxide
which can be filtered off.
Ca(HCO3) + Ca(OH)2
2CaCO3
+ 2H2O

29. REMOVAL OF PERMANENT HARDNESS
• TREATMENT WITH WASHING SODA: WASHING SODA REACTS WITH SOLUBLE CALCIUM AND MAGNESIUM
CHLORIDES AND SULPHATES TO FORM INSOLUBLE CARBONATES
• CALGON’S METHOD: SODIUM HEXAMETAPHOSPHATE(NA6P6O18) COMMERCIALLY KNOWN AS CALGON,
WHEN ADDED TO HARD WATER LEADS TO THE FORMATION COMPLEX ANIONS WHICH KEEPS MG2+ AND
CA2+ IONS IN THE SOLUTION.

30. • Ion exchange method: When sodium aluminium silicate
(zeolite/permutit) is added to hard water, exchange reaction
takes place.
• Synthetic resins method: Nowadays hard water is softened by
using synthetic cation exchangers. This method is more
efficient than zeolite process.

31. Hydrogen Peroxide
AN IMPORTANT CHEMICAL USED IN POLLUTION CONTROL
TREATMENT OF DOMESTIC AND INDUSTRIAL EFFLUENTS

32. PREPARATION
 ACIDYFING BARIUM PEROXIDE AND REMOVING EXCESS WATER BY
WVAPORATION UNDER REDUCED PRESSURE GIVES H2O2
 PEROXODISULPHATE ON HYDROLYSIS YIELDS HYDROGEN PEROXIDE
HO3SOOSO3H HYDROLYSIS 2HSO4 + 2H + H2O2
 Industrially it is prepared by the auto-oxidation of 2-alklylanthraquinols. In this case
1% H2O2 is formed. It is extracted with water and concentrated to 30% pressure. It can
be further concentrated to 85% by careful distillation under low pressure. The
remaining water can be frozen out to obtain pure H2O2
BaO2.8H2O + H2SO4 BaSO4 + H2O2 + 8H2O

33. Physical Properties
In the pure state, H2O2 is a very pale blue liquid with a melting point of 272.4 K, boiling
point of 423 K. It is miscible in water in all proportions and it form hydrates H2O2.H2O. A
30% solution of H2O2 is marketed as 100 volume hydrogen peroxide.

35. USES OF HYDROGEN PEROXIDE
1) USED AS HAIR BLEACH AND MILD DISINFECTANT
2)USEDTO MANUFACTURE CHEMICALS LIKE PER-CARBONATE
3)USED IN SYNTHESSIS OF CERTAIN FOOD PRODUCTS
4)USED IN INDUSTRIES AS BLEACHING AGENT
5)USED IN ENVIRONMENTAL CHEMISTRY

36. HEAVY WATER (D2O)
IT IS USED AS A MODERATOR IN NUCLEAUR REACTORS AND IN
EXCHANGE REACTIONS.
IT IS PREPARED BY EXHAUSTIVE ELECTROLYSIS OF WATER AS A BY-
PRODUCTIN SOME FERTILIZER INDUSTRIES.
IT IS USED FOR PREPARATION OF OTHER DEUTERIUM
COMPOUNDS:
CaC2 + 2D2O C2D2 + Ca(OD)2
SO3 + D2O 2SO4
AL4C3 + 12D2O 3CD4 +
4AL(OD)3

37. DIHYDROGEN AS A FUEL
HYDROGEN RELEASES LARGE QUANTITIES OF HEAT ON COMBUSTION. IT RELEASES
MORE ENERGY THAN PETROL, ALMOST THRICE. THE ONLY POLLUTANTS ARE OXIDES
OF NITROGEN ,WHICH CAN BE REDUCED BY INJECTING A SMALL AMOUNT OF
WATER IN THE CYLINDER TO LOWER TEMERATURE.

38. Done By
Kevin Anil
XI-M