2. In periodic table there are total 118 elements
are present .
But in nature there are more then 118
substances are present
Reason is that these atoms/ elements react
with each other to form new substances
which are called chemical compound.
Compounds are combination of two more
then two atoms joint together.
3. When atoms combine to give formation of
compound then properties of compound will
be different from the properties of atoms
which are responsible for compound
formation.
Consider an example
A + B AB
Two atoms (Compound)
4. Now properties of AB will different from
properties of A & B.
Consider typical example from chemistry
Sodium + Chlorine Sodium chloride
Na Cl NaCl
Where Na is metal, Silver like color and when
react with water become wet in this case
highly flammable
5. Cl is gas, greenish color, toxic in nature, by
inhaling it may cause headache, nausea and
may leads to damage respiratory system.
It was used as a weapon in first world war.
Now these two atoms combine to form NaCl
which is solid and common salt and daily we
use it our houses.
So two dangerous atoms combine and form
very safe compound
6. In compound two or more atoms combined
with each other by force of attraction this
force of attraction is called chemical bond
“Chemical bond is force of attraction which
hold two or more atoms together in form of
compound”.
Chemical bond is form in order atoms
become stable
7. Atoms in free form contain high energy and
low stability
Atoms in combined form(Compound) contain
low energy and high stability.
So when atoms combine due bond they lose
energy and get stability. Energy change
graph during formation of bond can be
represented as follow
8.
9. First when atoms are free they contain high
energy.
Down arrow shows that initially atoms have
high energy but as soon bond develop these
atoms are getting close to each other and
energy is decreasing at each point while
stability increasing at each point.
AS bond form then energy become
minimum.
10. Horizontal arrows shows that two atoms
bonded to each other in this stage the energy
is minimum and stability is maximum, this is
the point where atoms are bonded to each
other.
As bond break up then again atoms getting
away from each other and energy is
increasing again.
11. An upper arrow shows that two atoms
getting away from each other as a result of
bond breaking and energy is increasing at
each point while stability is decreasing at
every point.
This is entire energy change during formation
of chemical bond.
12. End of lesson
By: Muhammad Islam
(islam.chemist88@gmail.com)
Good luck
Editor's Notes
The above graph represents the change of energy during formation of bond (discussed in next slides)
