2. PREPARED BY
LEKSHMI.S.G
PHYSICAL SCIENCE
REG NO: 13357003
BNVCTE,THIRUVALLAM

4. All matter is made up of atoms.
Atoms of an element are
identical.
Each element has different
atoms.
Atoms can engage in a chemical
reactions.
Atoms can neither be created
nor be destroyed.
Atoms are indivisible.
Atomic Theory
John Dalton
(1776-1884)

5. atom has a positively charged
central part (nucleus)
Electrons are distributed
around nucleus
Mass of an atom is
concentrated at nucleus.
Compared with total volume
of an atom, the volume of
nucleus is meager
Rutherford’s Atomic
Model
Ernest Rutherford
(1871-1937)

6. Solar system Rutherford‘s atom model
Planetary model of atom

7. Bohr's Model of the Atom
Niels Bohr
1913

8. Bohr's Model of the Atom
 electrons orbit the nucleus like planets
orbit the sun

9. Bohr's Model of the Atom
 electrons fills the orbits closest to the
nucleus
e.g. fluorine:
#P = 9
#e-
= 9
#N = 10
9P
10N

10.  each orbit can hold a specific maximum
number of electrons
Shell maximum no: of
electrons
1 - K
2 - L
3 - M
4 - N
Bohr's Model of the Atom
2
8
18
32

11. Bohr’s Model
Nucleus
Electron
Orbit
Energy Levels

12. What is the structure of an atom?
• Nucleus - center of the atom
Home of Protons and Neutrons
Has a positive charge
• Proton
Has a relative mass of 1
Has a positive (+) charge
Determines the atomic number
Found inside the nucleus

13. What is the structure of an atom?
• Neutron
Has no (0) charge
Has a relative mass of 1
Found inside the nucleus

14. What is the structure of an atom?
• Electron
Has a negative (-) charge
Found outside the nucleus
• Rutherford atom model - electrons are
around the nucleus
• Bohr model – electrons are in specific
energy levels called shells

15. How are p, n, e related?
• No: protons = No: electrons
• No: protons = atomic number
• No: protons + No:neutrons = mass
number
• No: neutrons=mass no: - atomic no:

16. ATOMIC STRUCTUREATOMIC STRUCTURE
the number of protons in an atom
the number of protons and
neutrons in an atom
HeHe
22
44Atomic mass
Atomic number
number of electrons = number of protons