2. 400 BC 1799 1864 1897 1911
Democritus Proust Newlanda JJ Thomson Rutherford
1931
1534 1817 1869 1906
Bothe &
Copernicus Debelreiner Mendeleev JJ Thomson
Chadwick
1903
350 BC 1803 1866 1913
Wright
Aristotle Dalton Nobel Mosley
Brothers
1665 1826 1895 1908 1969
Newton Berzerius Röntgen Millikan Apollo 11
3. • Democritus argued all matter is made up of atoms.
400BC
• Aristotle argued regardless of the number of times you cut a form of
350BC matter in half, you would always have a smaller piece of that matter.
• Proust proposed the Law of Constant Composition.
1799
• Dalton formed atomic theory.
1803
• Döbereiner discovered law of triads.
1817
• JJ Thomson discovered the electron.
1897
4. • JJ Thomson demonstrated hydrogen had only a single
1906 electron per atom.
• Millikan found out the electric charge of the electron.
1908
• Rutherford proposed the nuclear atom as the result
1911 of the gold-foil experiment.
• Bothe & Chadwick discovered the neutrally-charged
1931 neutron.
5. • Berzelius published a table of atomic weights.
1826
• Newlands discovered the Periodic Table
1864
• Mendeleeve published a periodic table
1869
• Mosley proposed that the relationship was a function
1913 of the positive charge on the nucleus.
6. • Copernicus presented Helicentrism.
1534
• Newton discovered Universal gravitation.
1665
• Nobel invented Dynamite.
1866
• Röntgen discovered X-Ray.
1895
• Wright Brothers made the first airplane flight
1903
• Apollo 11 landed on the Moon for the first time.
1969
7. Democritus
Democritus, Greek philosopher, argued that
everything in the universe is made up with atoms but
people argued back that everything was made up with
the four factors (fire, air, dirt and water)
8. Aristotle
Aristotle’s main contribution to science was his
emphasis on careful observation and very detailed
classification. His ideas were highly influential in
Europe for about 1500 years. It was not until the
Renaissance that they were questioned, most notably
by Galileo. Aristotle’s system was not in itself rigid.
But it was used by many people in the Middle Ages to
justify and maintain the feudal system, a strict social
order by which kings ruled over lords, who in turn
ruled over peasant.
9. Joseph Louis Proust
Joseph Louis Proust published his law of definite
proportions stating that when compounds are
analyzed into their constituent parts they always
contain the same proportions of their elements by
weight. What we now know as stoichiometry led
Dalton to propose his atomic theory in 1803.
10. John Dalton
John Dalton he published a book called ‘A New System
of Chemical Philosophy’ in 1808. It had two main
points. One was that all chemical elements are
composed of very small particles called atoms, which
do not break up during chemical reactions. The other
was that all chemical reactions are the result of atoms
joining together or separating. Another important
feature of the book was its proposal that different
atoms weigh different amounts.
11. Döbereiner
Johann Wolfgang Döbereiner was a German scientist.
He discovered law of triads in 1817. Each of his triads
was a group of three elements. The appearance and
reactions of the elements in a triad were similar to
each other. The relative atomic mass of the middle
element in each triad was close to the average of the
relative atomic masses of the other two elements.
This gave other scientists a clue that relative atomic
masses were important when arranging the elements.
12. J.J. Thomson (1897 & Protons)
Joseph John Thomson was a British physicist. He
discovered the electron in 1897. This showed that the
atom contained smaller pieces, whereas John Dalton
had thought that atoms could not be broken down into
anything simpler.
Joseph John Thomson demonstrated that hydrogen
had only a single electron per atom. Previous theories
allowed various numbers of electrons in 1906
13. Robert Anderson Millikan
Robert Millikan was an American physicist. He did oil-
drop experiments in 1909. In the experiment he
measured the electric charges on tiny falling oil
droplets. His study established that any particular
droplet's electrical charge is a multiple of a
definite, fundamental value - the electron's charge.
14. Ernest Rutherford
Ernest Rutherford discovered X-Rays and uranium
radiation. Rutherford and his team carried out
important experiments into the structure of the
atom, using particles called alpha particles, which are
emitted by radioactive substances. From his
experiments, Rutherford built up a detailed picture of
the atom. He concluded that most atomic matter was
concentrated into a tiny nucleus in the middle, which
much lighter particles called electrons orbiting it, like
planets around the sun. In 1908, Rutherford was
awarded the Nobel Prize for Chemistry.
15. Walter Bothe & James Chadwick
In 1930, Walther Bothe and Herbert Becker described
an unusual type of gamma ray produced by
bombarding the metal beryllium with alpha particles.
James Chadwick recognized that the properties of this
radiation were more consistent with what would be
expected from Rutherford's neutral particle. Chadwick
proved the existence of the neutron earned him the
1935 Nobel Prize in physics. Not only did this singular
particle provide physicists with a superlative tool for
investigating the atom, it was also used to produce a
wide variety of new radioisotopes and permitted the
initiation of nuclear chain reactions.
16. Jöns Jakob Berzelius
Jöns Jakob Berzelius determined the atomic weights
of nearly all the elements then known. Dealing with so
many elements in so many compounds motivated his
creation of a simple and logical system of symbols—
H, O, C, Ca, Cl, and so forth—which is basically the
same as the system we use today, except that the
combining proportions of the atoms of elements in a
compound were indicated as superscripts instead of
our subscripts.
17. John Newlands
John Newlands proposed the conception of periodicity
among the chemical elements. He showed that if the
elements be arranged in the order of their atomic
weights, those having consecutive numbers frequently
either belong to the same group or occupy similar
positions in different groups, and he pointed out that
each eighth element starting from a given one is in
this arrangement a kind of repetition of the first, like
the eighth note of an octave in music.
18. Walter Bothe & James Chadwick
In 1930, Walther Bothe and Herbert Becker described
an unusual type of gamma ray produced by
bombarding the metal beryllium with alpha particles.
James Chadwick recognized that the properties of this
radiation were more consistent with what would be
expected from Rutherford's neutral particle. Chadwick
proved the existence of the neutron earned him the
1935 Nobel Prize in physics. Not only did this singular
particle provide physicists with a superlative tool for
investigating the atom, it was also used to produce a
wide variety of new radioisotopes and permitted the
initiation of nuclear chain reactions.
19. Mendeleev
Dmitri Mendeleev published a periodic table in 1869.
He also arranged the elements known at the time in
order of relative atomic mass, but he did some other
things that made his table much more successful.
He realised that the physical and chemical properties
of elements were related to their atomic mass in a
'periodic' way, and arranged them so that groups of
elements with similar properties fell into vertical
columns in his table.
He predicted the properties of an undiscovered
element that should fit below aluminium in his table.
20. Henry Mosley
In 1914 Henry Mosley stated the modern periodic law.
He said that when the elements are in order of
increasing atomic number (number of protons they
show a periodicity or repeating pattern of properties.
