Let's look at the position of hydrogen in the periodic table.
Hydrogen is placed in group 1.
You will see that hydrogen is placed in group 1
of the periodic table but the position of hydrogen
in the periodic table is contradictory. This is because hydrogen
shows properties which are similar to the alkali metals,
that is the group 1 elements and it shows
properties similar to the halogens that is group 7 elements.
Let's see how is hydrogen similar to the
alkali metals and the halogens.
Like all alkali metals, hydrogen has
1 electron in the valence shell.
Since hydrogen has only 1 electron which is present
in the valence shell. So, like all alkali metals,
hydrogen has 1 valence electron.
Another similarity is that since it has only 1 valence electron,
it can lose this 1 electron to stabilize it self.
Like all alkali metals, they stabilize themselves
by losing the 1 valence electron, when they lose 1 valence
electron, they satisfy the octate rule.
So, like all the alkali metals, hydrogen can lose
1 valence electron to stabilize itself.
Another chemical property of the alkali metals
is that they react with oxygen to form
the corresponding metal oxides.
Sodium forms sodium oxide, lithium form lithium oxide and
so on. So, like all the alkali metals hydrogen
reacts with oxygen to form hydrogen oxide
which we call water. Like all the alkali metals
hydrogen also reacts with oxygen to form
the corresponding oxide.
This is the reason why we place it
in group 1, since, it shows similarity to group 1
metals but at the same time hydrogen also
shows properties similar to the group 7
elements
that is halogens. Let's see how is hydrogen similar to halogens.
All the halogens are 1 short-
are 1 short of electron in the valence shell that
of the nearest noble gas.
Fluorine has an electronic configuration 2,7, the nearest
noble gas is neon which has
2,8 electronic configuration. So, the outer most shell
has 1 electron less than the nearest noble gas.
Similarly chlorine has 1 electron
less in the valence shell
like the nearest noble gas. Similarly, hydrogen has 1 valence electron,
the nearest noble gas to hydrogen
is helium which has 2 valence electrons.
So, like all the halogens
hydrogen has 1 electron less than
the nearest noble gas. So, this is how it is
similar to halogens. Another similarity
like all halogens gain electrons to complete the octate,
similarly, hydrogen- hydrogen has
1 electron, it gains 1 electron to complete the duplet structure.
So, like all halogens gain electrons, similarly, hydrogen gains
1 electron to
stabilize itself that is to complete the duplet structure.
Halogens- Fluorine, Chlorine
they exist in the gaseous state, similarly we know
that hydrogen it exists in the gaseous state. So, like halogens
hydrogen is also a gas.
The atomicity of all the halogens is
2 that is in 1 molecule there are 2
atoms of fluorine. In 1 molecule there are 2 atoms of
chlorine and similarly for bromine, iodine and so on. So, the atomicity of halogens
is 2.
We know that hydrogen also exists
in the form of H2,
so, in 1 molecule of hydrogen there are 2 atoms of hydrogen.
So,the atomicity of hydrogen is 2
like all the halogens.
What is the atomicity of hydrogen?
In one molecule of hydrogen, we know
there are hydrogen atoms, so, the atomicity
of hydrogen is 2.
So, these are the similarities of hydrogen with halogens.
So because of this, hydrogen showing similar properties
to alkali metals and properties similar to halogens,
the position of hydrogen in the periodic table
is till date contradictory. For convinience
we place it in group 1 that is in
the alkali metal series but the position of hydrogen in the
periodic table is till date not resolved.
