2.  An Atom is the smallest particle of any
substance . Atoms so small in size that they
can be only seen with the help of
microscope . The size of a atom is
measured in picometers . The name atom
comes from a Greek word which means
indivisible which cannot be divided further
or which cannot be cut further . An atom
consists of protons , electrons , neutrons .

3. A figure of atom which shows electrons , protons and
neutrons

4.  Electrons are negatively charged particles
present in an atom . Electrons are
extremely small compared to all the other
parts of the atom . The mass of an electron
is almost 1000 times smaller than a proton .
Between 1838 and 1851 British philosopher
found out that the atom is surrounded by
some particles which have a electric charge
After some more years it was found out as a
electron .

5. We can only see the electrons through such microscopes

6.  Protons and neutrons are in the center of
the atom which together form the nucleus
of the atom . The protons have positive
charge on the other hand neutrons have no
charge . The protons and neutrons together
form a nucleon . The electrons revolve
around the nucleons (protons and neutrons)
in particular orbits .

7.  In 1800s John Dalton performed some
experiments as a result he found out the
existence of atom . In 1897 J.J Thompson
discovered electrons and these electrons
are present in the atom . His model was like
a watermelon the red part inside is like the
neutrons and the black seeds are like the
electrons inside it .

8.  John Dalton was a english chemist ,
physicist , meteorologist .
 Main points of Daltons theory :-
1. Elements are made of very small particles
called atom .
2. Atoms can’t be subdivided , destroyed ,
created .
3. In chemical reactions atoms are combined
, separated , rearranged

9.  Sir Joseph john Thompson was born on 18
December 1856 . He was an english
physicist . In 1906 he was awarded the
Noble Prize in physics for the discovery of
electron . He was also awarded various
medals and prizes like Adams prize , Royal
prize , Hughes medal , Franklin medal ect.

11. Each part of atom is labeled +,- signs . These
signs refer to the charge of particles . The
protons always have positive charge and the
electrons have a negative charge . If the
charge is neutral the number of protons and
electrons are equal . The neutrons have 0
charge that is they are neutral . The neutral
charge is also known as 0 .

12. Structure
of atom

13.  The atomic mass is the
weight of a atomic
particle . The protons
and the neutrons are
responsible for almost
all the weight of an
atom .
 In chemistry and
physics the atomic
number of chemical
element is the number
of protons found in
the nucleus of atom .
It is represented by Z .
The symbol Z comes
from the german word
‘Atomazal’ means
atom

14. Rutherford had conducted experiments in which
he shot relatively large, charged particles
(alpha particles) at a thin gold foil. From
these results, Rutherford concluded that each
atom was mostly empty space, but also
contained a dense region central mass, which
his alpha particles could not pass through. He
also concluded that this central mass must
have a positive charge, to deflect the
positively charged alpha particles. Rutherford
and Bohr pictured the arrangement of the
atom's parts to look like our solar system.

17.  An atom is the smallest unit of matter that
defines the chemical elements.
Every solid, liquid, gas, and plasma is made up
of neutral or ionized atoms. Every atom is
composed of a nucleus made of one or
more protons and usually an equal or similar
number of neutrons (except hydrogen which
has no neutrons . Protons and neutrons
together are called nucleons. The nucleus is
surrounded by one or more electrons. Over
99.94% of the atom's mass is in the nucleus.

18. Isotopes of carbon are 12c and 14c

19.  An isotope is a form of chemical who’s atomic
nucleus contains specific number of neutrons
in additions to the number of protons that
define the element . The isotope of an
element is defined by the nucleon number,
which is the sum of the number of protons and
the number of neutrons in the atomic
nucleus. For example, 16 O represents oxygen-
16, which has 8 protons and 8 neutrons,
while 12 C represents carbon-12, with 6 protons
and 6 neutrons .