Page 160 - Chemistry ICSE Class IX

148 ICSE Chemistry – 9
ƒ 'NGEVTQPKE EQPſIWTCVKQP Both hydrogen and halogens are one
electron short of saturation in their outermost shell. After gaining
one electron, they acquire stable con guration of the nearest noble
gas. Thus, both behave as univalent nonmetals as shown below.
–
H + e o H – He
(1) (2) (2)
–
Cl + e o Cl – Ar
(2, 8, 7) (2, 8, 8) (2, 8, 8)
–
Br + e o Br – Kr
(2, 8, 18, 7) (2, 8, 18, 8) (2, 8, 18, 8)
ƒ *[FTKFGU CPF JCNKFGU Hydrogen combines with alkali and alkaline
earth metals to form hydrides similar to halides.
H 2 + 2Na o 2NaH Cl + 2Na o 2NaCl
2
hydrogen sodium sodium hydride chlorine sodium sodium chloride
H 2 + Ca o CaH 2 Cl + Ca o CaCl 2
2
hydrogen calcium calcium hydride chlorine calcium calcium chloride
The molten hydrides on electrolysis produce hydrogen at anode, like
chlorine from molten chlorides.

1
electrolysis
electrolysis
–
–
H o 1 H (g) + e – Cl o Cl (g) + e –
2 2 2 2
hydride ion (at anode) chloride ion (at anode)
ƒ 5WDUVKVWVKQP QH J[FTQIGP D[ JCNQIGPU Halogens easily replace
hydrogen from compounds such as hydrocarbons. For example, in
methane
CH (g) + Cl (g) o CH Cl(g) + HCl(g)
2
4
3
methane chlorine chloromethane
CH Cl(g) + Cl (g) o CH Cl (g) + HCl(g)
2
2
2
3
dichloromethane
and so on.
Properties of Hydrogen not Common to Both the
Alkali Metals and Halogens
Hydrogen has some properties which neither resemble alkali metals nor
halogens. For example,
ƒ 0CVWTG QH QZKFG The oxide of hydrogen, H O is neutral, while
2
the oxides of halogens, e.g., Cl O, ClO , Cl O , etc. are acidic and
7
2
2
2
the oxides of alkali metals, e.g., Na O, K O, etc. are basic.
2
2
ƒ 'NGEVTQPKE EQPſIWTCVKQP Hydrogen atom has no inner electrons and
no unshared electrons.
Isotopes of Hydrogen
What are the isotopes of hydrogen

There are three isotopes of hydrogen. These are — protium, deuterium and
tritium. These three isotopes of hydrogen are shown in Fig. 6.1.