Hydrogen
is the first element of the periodic table. Its atomic number is 1,
which indicates the presence of only one electron in the atom of
hydrogen. This electron is present in its first shell. Hydrogen
resembles both alkali metals (group I A) as well as halogens (group VII
A) therefore its position is said to be anomalous.
Some Basic Features of Hydrogen
| Symbol | H |
| Molecular formula | H2 |
| Atomic number | 1 |
| Mass number | 1 |
| Atomic mass | 1.008 |
| Molecular mass | 2 |
| Electronic configuration | 1 |
| Valency | + 1 or - 1 |
| Isotopes of Hydrogen | 11H Protium |
| 21H Deuterium | |
| 31H Tritium |
Remember :
Isotopes are atoms of the same element having the same atomic number, but different mass number.
Properties of Hydrogen that Resemble Alkali Metals
Electronic configuration
Hydrogen atom has one electron in its valence shell like alkali metals.
Valency
Hydrogen generally shows + 1 valency like alkali metals.
Metallic character
It readily loses its electron to form a positive ion like other alkali metals.
Combination with non-metals
Hydrogen, like the alkali metals, combines readily with non-metals like halogens, oxygen, sulphur, etc.
Reducing agent
Hydrogen is a good reducing agent like other alkali metals.
Properties of Hydrogen that Resemble Halogens
Non-metallic character
Hydrogen is a non-metal like halogens.
Atomicity
Like halogens, hydrogen is diatomic (H2) whereas metals are monoatomic.
Valency
Like halogens, hydrogen may also show 1 valency by accepting an electron. Example: NaH (Sodium hydride)
Nature of compounds
Hydrogen combines with non-metals like carbon, silicon, etc. to from covalent compound like halogens.
Examples: CH4 and CCl4.
Remember :
In
1766, Henry Cavendish, an English chemist, discovered hydrogen, by
treating iron with dilute sulphuric acid. He also proved that when
hydrogen is burnt in air, water is the only product obtained. It was
"hydrogen", meaning "water producer" (Hydro = water,
gen
= generator or producer). Cavendish called this gas "Inflammable gas".
Hydrogen has three isotopes namely protium, deuterium and tritium.
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