#### Lesson / Chemistry / Hydrogen

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### Notes on Hydrogen

354 / May-30-2021 12:15:46 By- srijan /

Symbol: 'H'
Atomic Number: '1'
Atomic Mass: '1.008'
Valency: '1'
Electronic Configuration: '1s1'

Position in the periodic table:
On the account of it's electronic configuration physical and chemical properties. Hydrogen is placed in the group first A of the periodic table along with alkali metals or in the group seventh A with halogen.

Hydrogen has an equal tendence to gain or loose one electron fi=or stable configuration when it loose one electron (gives ) it becomes positively charge ( H+ion ) and behaves like an alkali metals of group IA

H → H+ + e-
Na → Na+ + e-
When it gain one electron from other atoms it becomes negatively charge i.e. (H-ion) and thus behaves like halogens of the grop VIIA.

H + e-→ H- F+ + e-→ F--

Similarity with alkali metal (group IA)
i) Both hydrogen and alkali metal have one electron in their outermost orbital.

ii) Hydrogen like alkali metals is highly electropositive and can loose one electron to form H+ ion.

iii) Hydrogen is strong reducing agent like a alkali

iv) Hydrogen and alkali metals both have a strong affinity of non- metals. egf: HCl, H2 O, H2 S, NaC, Na2 O

Dissimalarities behaviour from the alkali metal.
i) Hydrogen is a gas at a room temperature while alkali metal are solid.
ii) Hydroge is a non - metal while alkali metals are typical metals.
iii) Hydrogen is diatomic (H2) while alkali metals are monoatonic in a vapour state.

iv) Compounds of hydrogen are predominantly co-valet in nature while those of alkali metal are ionic in nature.

Similarity with Halogen(Group VII A
i) Both hydrogen and halogen behaves as a monovalent electronegative elements.
ii)Hydrogen and halogen both are non-metal
iii) Like halogens, hydrogen gains one electron to form hydraide ion and thus exibits electronegative character.
iv) Both hydrogen and halogen of diatomic molecule =s with co-valent bond. eg: H2, Cl2, etc

Dissimalarities with Halogen

i) Oxides of hydrogen is neutral but oxides of halogen are acidic.
ii) The tendence of hydrogen to gain an electron is much less compare to halogen which can form halide ions very rarely gaining an electron.

Isotopes of Hydeogenr
Isotopes are the atoms of the same of the element having same atomic number but different mass nmber. Hydrogen has three isotopes namely:

1) Protium(or hydrogen): 11 H

Uses:

a) It is used in the Haber's process for synthesis of ammonia gas.
b) It is used as reducing agent in metrallorgical operation.

2) Deuterium (or heavy hydrogen):

21H or, D
Atomic number = 1
mass number = 2
stability = stable

Uses:
a) It is used as tracers in the study of reaction mechanism.
b) It is used in bombarding an atom because of it's speed.

3) Tritium:

Symbol: 13H OR, T
Atomic number = 1
Atomic mass = 3

Uses:
a) It is used as an artficial radioactive tracers in chemistry, medicine and biology.
b) It is used in nuclear fusion reaction to produce a huge amount of energy which is used in hydrogen bomb.

TYPE OF HYDROGEN:

1) Molecular hydrogen or Dihydrogen: It can be prepared by the action of dilute sulphuric acid on a zinc metal.
Zn + H2 SO4 → ZnSO4 + H2
Or,
[H] + [H] → H2

2) Atomic Hydrogen: When a stream of hydrogen gas under pressure is passed through an electric arc between tungstens rods , atomic hydrogen is produced.
$\dpi{150}&space;\fn_cm&space;H_{2}\leftrightharpoons&space;2H&space;\rightarrow&space;104&space;KCal$
atomic hydrogen

VVI Topic
3) Nascent Hydrogen
The newly born hydrogen is nascent hydrogen.
The hydrogen obtained during the chemical reaction in the begining which is in association with the substance to be reduce is called nascent hydrogen. It is represented by [H].

Molecular hydrogen is not capable of reducing acidified KMnO4 solution, k2Cr2O7 solution and FeCl3 solution. But nascent hydrogen reduces KMnO4 ,K2Cr2O7 and FeCl3 solution. This can be shown by the chemical reaction. 1) KMnO4 + H2 SO4 + H2 → No reaction.
2KMnO4(Pink) + 3 H2SO4 + 10[H] $\dpi{150}&space;\fn_cm&space;\xrightarrow[]{Zn/H_{2}SO_{4}}$ K2SO4 + MnSO4(colourless) + 8H2O

2) K2Cr2O7 + H2SO4+ H2 → No reaction

K2Cr2O7(orange) + H2SO4 + 6[H](in presence of Zn/ H2SO4) →K2 SO4 + Cr2(SO4)3(green) + 7 H2 O

3) FeCl3 + H2 → No Reaction
FeCl3 + [H] (in presence of Zn/H2SO4→ FeCl2(Slightly greenish) + HCl