This document provides an overview of the structure of an atom. It discusses: 1) Early atomic models including Thomson's model of a uniform positive charge with embedded electrons, and Rutherford's model with a small, dense nucleus and orbiting electrons. 2) The three main subatomic particles - protons, neutrons, and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. 3) Key atomic properties including atomic number, the number of protons; mass number, the sum of protons and neutrons; and atomic weight, the relative weight of an atom compared to hydrogen. 4) Isotopes, atoms of the same element with the

1. WELCOME
TO THE WORLD OF
THE STRUCTURE OF AN ATOM
ISHA EKBOTE

2. THIS WORLD CONTAINS 5
CONTINENTS NAMELY:
 WHAT IS AN ATOM ?
 DISCOVERY OF AN ATOM
 THE PARTICLES OF AN ATOM
 ATOMIC NUMBER ; MASS NUMBER AND
WEIGHTS
 ISOTOPES

3. AN ATOM
 An atom is the smallest
particle of an element.
 Atoms come together to
make molecules or
particles .
 There are many different
types of atoms, each with
its own name , mass and
size.
 They themselves are
made up of 3 kinds of
particles , protons
(positively charged),
neutrons (have no
charge) and electorns
(negatively charged).
 In atoms the no. of
protons and no. of
elelctrons are equal.

4. DISCOVERY OF AN ATOM
 In 1803 John Dalton gave the first systematic
idea of the structure of the atom.
 He suggested that, atoms are small particles
and they are indivisible.
 Atoms cannot be created or destroyed.
 Atom is the smallest unit of matter that takes
part in a chemical reaction.
 In 1897, sir J.J.Thomson discovered electron.
 He carried out detailed and concluded that atom
is not the last and ultimate particle of
matter but consists of some fundamental
particles negative & positive charge.

5.  These particles were called as electrons and
protons respectively.
 According to Thomson’s model, atom was
supposed to be a homogeneous sphere
of positive charge, negatively charged
electrons are embedded in it.
 In 1911, Ernest Rutherford suggested that
atom is a hollow sphere and most of the
mass of the is concentrated in the of the
atom.

6. J.J. THOMSON

7. THOMSON’S ATOMIC MODEL
 As per Thomson’s atomic model, atom is
solid.
 There is no empty space.
 There is no nucleus in the Thomson’s
atomic model.
 The positive charge in the atom is
uniformly distributed.

8. THOMSON’S ATOMIC MODEL
Spherical cloud of
positive charge
Electrons

9. ERNEST RUTHERFORD

10. RUTHERFORD’S ATOMIC MODEL
 As per Rutherford’s atomic model atom
is hollow.
 With lot of empty space.
 The nucleus is at the center of the as per
Rutherford’s atomic model.
 The positive charge is concentrated in
the nucleus.
 Electrons revolve around the nucleus in
specific orbit.

11. RUTHERFORD’S ATOMIC MODEL
Nucleus (proton & neutron)
Electrons
Electronic Orbits

12. NEILS BOHR

13. NEILS BOHR ATOMIC MODEL
 Neil Bohr in 1913, specified the distribution
of electrons in different orbits.
 Bohr’s model of an atom suggest no. of
circular orbits around the nucleus, in which
electrons are distributed.
 He thought of an atom as a tiny solar
system, nucleus as the sun and electrons as
the planets.
 Thus according to him atom is made up of 2
parts, nucleus and extra-nuclear part.

14. NEILS BOHR’S ATOMIC MODEL
Electrons
Orbit
Nucleus

15. THE PARTICLES OF AN ATOM

16. PROTONS
 The protons have a positive charge.
 Protons are represented by the (p+).
 Protons are situated in the nucleus of an
atom.
 The number of protons in the nucleus
determines what chemical element the
atom belongs to.
 The mass of proton is considered to 1 unit.

17. ELECTRONS
 Electrons have a negative charge.
 They are represented by the symbol (e-).
 Electrons revolve around the nucleus in
specific orbit.
 The mass of electron is negligible.
 The electrons in an atom are bound to the
atom by the electromagnetic force.

18. NEUTRONS
 Neutrons are neutral as they do not have
any charge.
 They are represented by the symbol(n).
 Neutrons are situated in the nucleus of an
atom.
 The mass of neutrons is nearly equal to the
mass of the protons.
 The number of neutrons determines what
isotope of the element it is.

19. ATOMIC NUMBER
&
ATOMIC MASS NUMBER
&
ATOMIC WEIGHTS

20. ATOMIC NUMBER
 The number of protons and electrons in an
atom is called the atomic number.
 The atomic number is represented by the
symbol(Z).
 All atoms of same element have same
atomic number.
 The atomic number uniquely identifies a
chemical element .

21. ATOMIC MASS NUMBER
 Atomic mass number (A) is equal to the
sum of the number of protons and
neutrons in the nucleus.
 Atomic mass number is represented by the
symbol (A).
 Isotopes same element have different
atomic number.
 The atomic number is always an integral
number.

22. ATOMIC WEIGHTS
 The relative weight of an atom of an
element is called the atomic weight of the
element.
 The weight of atoms is very small.
 Hence it is convenient to give their actual
weights.
 ATOMIC WEIGHT OF ELEMENT=AVERAGE WEIGHT OF ATOMS OF ELEMENT
WEIGHT OF AN ATOM OF HYDROGEN
 EG:- Hydrogen = 1
Oxygen = 16
Nitrogen =14

23. ISOTOPES & IT’S PROERTIES
 Atoms of the same element having same
atomic no.& but different atomic mass no.
are called as isotopes of that element.
 Properties on isotopes:-
 Isotopes exhibit same chemical properties.
 Isotopes differ in physical constants and
weights.
 Isotopes occupy the same position in
periodic table.

24. ISOTOPES OF HYDROGEN
 Hydrogen has 3
isotopes, protium,
deuterium and
tritium having 1
,2 and 3
respectively.
They have 1
proton and 1
electro each , but
deutrium has 1
and tritium has
2 neutrons
respesctively

25. THANK YOU