Page 159 - Chemistry ICSE Class IX
P. 159
Study of the First Element : Hydrogen 147
Hence, hydrogen is assigned a separate location on the left side of the
periodic table on top of the Group IA, but separated from the other elements
of Group IA to indicate distinctive character of hydrogen.
Resemblance with Alkali Metals
How does hydrogen resemble alkali metals
Hydrogen resembles alkali metals in the following aspects:
'NGEVTQPKE EQPſIWTCVKQP The hydrogen atom has only one electron in
its outermost shell, like the alkali metals.
Element H Li Na
Atomic no. 1 3 11
Electronic con guration 1 2, 1 2, 8, 1
%CVKQP HQTOCVKQP Hydrogen, like alkali metals, forms singly charged
cation by losing its outermost electron.
H o H + + e –
Na o Na + + e –
#HſPKV[ HQT PQPOGVCNU Both hydrogen and alkali metals combine
with halogens to form halides, with oxygen to give oxides and with
sulphur to give sulphides. For example,
HCl H O H S
2
2
NaCl Na O Na S
2
2
'NGEVTQRQUKVKXG PCVWTG Hydrogen is displaced from acids by active
metals. In this reaction, hydrogen behaves as an electropositive
element. For example,
Zn(s) + dil. H SO o ZnSO (aq) + H (g)
2
2
4
4
It is further supported by the fact that when an aqueous solution of
hydrogen chloride or a molten alkali metal halide is electrolysed, both
hydrogen and alkali metals are liberated at the cathode.
HCl(aq) o H + + Cl –
+
–
2H + 2e o H (g)
2
liberated at cathode
NaCl (molten) o Na + + Cl –
–
Na + + e o Na
liberated at cathode
4GFWEKPI EJCTCEVGT Hydrogen, like alkali metals, acts as a strong
reducing agent.
'
CuO(s) + H (g) o Cu + H O
2
2
copper(I) oxide hydrogen copper
B O 3 + 6K o 2B + 3K O
2
2
boron trioxide potassium boron
(an alkali metal)
Resemblance with Halogens
How does hydrogen resemble halogens
Hydrogen resembles halogens in the following aspects:
0QPOGVCNNKE PCVWTG CPF CVQOKEKV[ Hydrogen is a gas, like uorine
and chlorine. Its molecule H is diatomic like F , Cl , Br and I .
2
2
2
2
2
