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The name hydrogen comes
Electronic Configuration 1s1
from Greek words “Hydro
(meaning water) and genes
(Meaning creator). It was
Atomic Number 1
named by French Chemist
Antoine Lavoisier because
Electronegativity 2.1 when it burns it creates
water.
Position of hydrogen in the periodic table :
Position for hydrogen is not fixed in the periodic
table due to following reasons :
(1) Hydrogen resembles group 1 elements. Previous Year’s Question
(Alkali metals).
(2) Hydrogen resembles group 17 elements.
The ionization of hydrogen atom
(Halogens).
would give rise to [AIPMT]
(3) Hydrogen exhibits other properties which
(1) Hydride ion
different from both alkali metals and
(2) Hydronium ion
halogens.
(3) Proton
(4) Hydroxyl ion
Types of hydrogen :
(1) Atomic Hydrogen :
Electric spark
H — H
200°C
→ 2H (Atomic hydrogen)
, DH = + 104.5 Kcal. Concept Ladder
y When hydrogen gas is passed through
Process of dissociation and
an electric arc between two tungsten
recombination of hydrogen
filaments, hydrogen s dissociated into
is utilized in oxy-hydrogen
atoms.
torch.
y Used for welding purpose.
Electric arch
(2) Nascent Hydrogen : When hydrogen H2 → 2H
(Atomic
is passed through acidified potassium hydrogen)
permanganate solution or FeCl3 solution H + H → H2 + energy
neither of them is reduced however when
Zn pieces are added both gets reduced.
Zn + H2SO4 (dil.) → ZnSO4 + 2[H]
Nascent
Hydrogen
hydrogen
1.
, KMnO4 + H2SO4 + H2 → No reaction
Concept Ladder
Similarities of hydrogen with alkali metals : About 10% of the weight
(i) Electronic configuration : Alkali metals of living organism is
and hydrogen has only one electron hydrogen mainly in water,
in their outer shell. proteins and fats.
(ii) Electropositive character : Like the alkali H2 is believed to be
metals hydrogen has a tendency to lose one of three elements
its electron to form unipositive ion. produced in the Big Bang.
The others are He and Li.
(iii) Oxidation state : Hydrogen, like alkali
metals have +1 oxidation state.
(iv) Affinity for non-metals : H2 as well as alkali
metals (Na, K, Rb etc.) have a strong affinity
towards non-metals.
Non-Metal Hydrogen Alkali Metal Compounds
Chlorides HCl NaCl KCl
Oxides H2O Na2O K2O
Sulphides H2S Na2S K2S
(v) Valency : Alkali metals as well as hydrogen Rack your Brain
show electrovalency of +1.
(vi) Reducing nature : Hydrogen-like alkali Why hydrogen is not termed as
metals, acts as reducing agent. s-block element despite it is
placed in Ist group?
Hydrogen
2.
,Difference of hydrogen with alkali metals :
(i) Non-metallic character : Hydrogen is a
non–metal while alkali metal are metalic.
Concept Ladder
(ii) Nature of oxide : Nature of oxide of hydrogen
is neutral while oxides of alkali metals Hydrogen shows dual
are basic in nature. nature. It behaves as
(iii) Atomicity : Hydrogen is diatomic in electropositive element
nature (H2) while alkali metals are like alkali metals as it
monoatomic. can lose the planetary
(iv) Nature of compounds : Nature of compounds electron. It also behaves as
of hydrogen with halogens (HCl, HBr, HF, HI) an electronegative element
are low boiling covalent compound while like halogens as it can
halides of alkali metals are low melting gain one more electron to
ionic solids (LiF, NaCl, KBr, etc.) saturate 1s subshell.
(v) Ionisation energy : Ionisation energy
of hydrogen is very high in comparison
to alkali metals.
Element Hydrogen Lithium Sodium Potassium
IE (kJ mol–1) 1312 520 495 418
Similarities of hydrogen with halogens :
(i) Electronic configuration : Electronic
configuration of hydrogen resembles the
halogens in having one electron less than
the next inert gas in its atom.
(ii) Diatomic nature : Like-hydrogen halogens Previous Year’s Question
are also diatomic. (H2, F2, Cl2, Br2)
(iii) Non-metallic character : Hydrogen as well One would expect proton to have
as halogens are non-metallic. very large [AIPMT]
(iv) Electro-negative nature : Hydrogen as (1) Charge
well as halogens can gain an-electron to (2) Ionization potential
form negative ion. (3) Hydrotion energy
H + e– –––→ H– ; Cl + e– –––→ Cl– (4) Radius
(v) Oxidation state : Hydrogen like halogens
show –1 oxidation state.
Hydrogen
Differences with halogens : Concept Ladder
(i) Nature of oxide :
Every hydrogen atom in
our body is likely 13.5
billion years old because
they were created at the
birth of the universe.
(ii) Absence of lone pair of electrons :
Hydrogen is about 14
times lighter than air.
(iii) Less electro-negative : Hydrogen is less
electro-negative than halogens.
Hydrogen
4.
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