Leucippus was an early Greek philosopher who developed the theory of atomism. He believed that everything is composed of indivisible atoms that have always and will always be in motion. He had a student named Democritus who expanded on his atomic theory. Robert Boyle later advanced the idea that basic elements are particles or corpuscles of different sizes and shapes that can combine to form chemical substances.

3. Leucippus or Leukippos was
He was a (born c. 460 —
one of the earliest Greeks to
died c. 370 BC) Greek
develop the theory of
philosopher.
atomism
• He was an Ancient Greek
Philosopher born • He was born in Miletus and spent
in Abdera, Thrace in Greece. the rest of his life in Abdera.
Leucippus was his mentor. Democrituswas his student.
• Yuh. Democritus.
• Yuh. Leucippus.

4.  held that everything is composed of "atoms―
 ―Atoms‖ are physically, but not
geometrically, indivisible.
 that between atoms lies empty space; that atoms
are indestructible;
 have always been, and always will be, in motion
 that there are an infinite number of atoms
 There are different kinds of atoms, which differ
in shape, and size.
 Democritus said "The more any indivisible
exceeds, the heavier it is." But his exact position on
weight of atoms is disputed.

6. Atomic Theory ROBERT BOYLE
Robert Boyle FRS (25  Boyle is best remembered for Boyle's law, a
January 1627 – 31 physical law that explains how the pressure and
volume of a gas are related.
December 1691) was a
17th century natural  He advanced the view that the basic elements
of matter are "corpuscles," or particles, of
philosopher, chemist, ph
various sorts and sizes. Boyle believed that
ysicist, and iventor, also these corpuscles were capable of arranging
noted for his writings themselves into groups, and that each group
in theology. constituted a chemical substance.
He is best known  He successfully distinguished between
for Boyle's law. mixtures (substances mixed together) and
compounds (chemically bonded substances)
and showed that a compound can have very
different qualities from those of its
constituents.

7. Antoine
Lavoisie
r consider
I
nature a vast  Born: 26 August 1743
chemical  Birthplace: Paris, France
laboratory in  Died: 8 May 1794 (beheading)
which all kinds Best Known As: French chemist
of composition who proved the law of conservation of
and mass
decompositions  Because of his achievements he is
are formed. sometimes called the father of
Antoine modern chemistry.
Lavoisier

8. Antoine Lavoisier’s contribution to atomic theory
 Antoine Lavoisier was the first person to
make good use of the balance.
 After a visit with Priestly in 1774, he began
careful study of the burning process. He
proposed the Combustion Theory which
was based on sound mass measurements.
 He named oxygen.
 He also proposed the Law of Conversation
of Mass which represents the beginning
of modern chemistry.

9. Joseph Proust


10. Joseph Proust
 Joseph Proust proposed the the Law of
Constant Composition in 1799.

 Law of Definite Proportions ( also called Law of
Constant Composition) –states that a given
compound always has the same elements in the same
proportion by mass.

11. J. Berzelius (Jöns Jacob Berzelius)
 Jöns Jacob Berzelius (20 August 1779 – 7 August
1848) was a Swedish chemist. He worked out the
modern technique of chemical formula notation, and
is together with John Dalton, Antoine
Lavoisier, and Robert Boyle considered a father of
modern chemistry.

12.  The most notable of Berzelius's contributions to chemistry
was his development of a rational system of atomic symbols.
 Around 1810 Berzelius was working to confirm John
Dalton's atomic theory as well as Proust's law showing
that separate elements always combined in whole-number
proportions.
 Berzelius came to the conclusion that the existing system
of denoting elements and compounds was a hindrance. In
establishing his own atomic symbols,
 He stated that "it is easier to write an abbreviated word
than to draw a figure which has little analogy with words"
Berzelius opted to use the first letter of the Latin name
for each element as its symbol.

13.  John Dalton (6 September 1766 – 27 July
1844) was an
English chemist, meteorologist and physicist.
He is best known for his pioneering work in
the development of modern atomic
theory, and his research into colour
blindness (sometimes referred to as
Daltonism, in his honour).

14.  All matter is made of atoms. Atoms are
indivisible and indestructible.
 All atoms of a given element are identical in
mass and properties
 Compounds are formed by a combination of
two or more different kinds of atoms.
 A chemical reaction is arearrangement of
atoms.

15. J.J Thomson
• Sir Joseph John "J. J." Thomson, (18
December 1856 – 30 August 1940) was aBritish
physicist and Nobel laureate.
• He is credited for the discovery of
the electron and of isotopes, and the invention of
the ,mass spectrometer.

16. JJ Thomson's major contributions to
the atomic theory..
• His atomic theory identified that electrons inside an atom could
show, meaning that atoms were not invisible.
Thomson suggested that the model of an atom as a sphere of
positively charged matter with negatively charged electrons
surrounding them.
• He stated that electrons were positioned by electrostatic forces.
• After the discovery of the electron and proton as subatomic
particles J.J. Thomson had started to discover atomic theory that
gives complete explanation of atomic structure.According to
Thomson protons are embed in the atoms like a water melon and
electrons are present in atoms to make the atom electrically
neutral.

17. ERNEST RUTHERFORD
 Ernest Rutherford, 1st Baron
Rutherford of Nelson (30 August 1871
– 19 October 1937) was a New Zealand-
born British chemist and physicist who
became known as the father of nuclear
physics
 He was awarded in 1908 "for his
investigations into the disintegration of
the elements, and the chemistry of
radioactive substances".

18. RUTHERFORD'S ATOMIC
THEORY -
ELECTRONEGATIVITY
 Ernest Rutherford publishes his atomic theory
describing the atom as having a central positive
nucleus surrounded by negative orbiting electrons.
 Rutherford came to this conclusion following the
results of his famous gold foil experiment.
 Rutherford found that although the vast majority
of particles passed straight through the foil
approximately 1 in 8000 were deflected leading
him to his theory that most of the atom was made
up of 'empty space'.

19. Niels Bohr
 Niels Henrik David Bohr (October
1885 – November 1962) was
a Danish physicist who made
foundational contributions to
understanding atomic
structure and quantum mechanics, for
which he received the Nobel Prize
in Physics in 1922.

20. Bohr’s Atomic Theory
 Neils Bohr postulated based on quantum theory
that electrons travel around an atomic nucleus in
a stationary orbit.
 Relegates the number of valence electrons to the
Periods of a periodic table
 Fully explains ionic and covalent bonding
 His work also led to the theory of different energy
levels in atoms, that is if an electron drops from a
higher to a lower orbit, it must release energy.