350 BC

Aristotle

1803

Dalton

1866

Nobel

1903

Wright

Brothers

1913

Mosley

1665

Newton

1826

Berzerius

1895

Röntgen

1908

Millikan

1969

Apollo 11

400 BC

Democritus

1799

Proust

1864

Newlanda

1897

JJ Thomson

1911

Rutherford

1931

Bothe &

Chadwick

1906

JJ Thomson

1869

Mendeleev

1817

Debelreiner

1534

Copernicus

400BC• Democritus argued all matter is made up of atoms.

350BC

• Aristotle argued regardless of the number of times you cut a form of matter in half, you would always have a smaller piece of that matter.

1799• Proust proposed the Law of Constant Composition.

1803• Dalton formed atomic theory.

1817• Döbereiner discovered law of triads.

1897• JJ Thomson discovered the electron.

1906

• JJ Thomson demonstrated hydrogen had only a single electron per atom.

1908• Millikan found out the electric charge of the electron.

1911

• Rutherford proposed the nuclear atom as the result of the gold-foil experiment.

1931

• Bothe & Chadwick discovered the neutrally-charged neutron.

1826• Berzelius published a table of atomic weights.

1864• Newlands discovered the Periodic Table

1869• Mendeleeve published a periodic table

1913

• Mosley proposed that the relationship was a function of the positive charge on the nucleus.

1534• Copernicus presented Helicentrism.

1665• Newton discovered Universal gravitation.

1866• Nobel invented Dynamite.

1895• Röntgen discovered X-Ray.

1903• Wright Brothers made the first airplane flight

1969• Apollo 11 landed on the Moon for the first time.

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)

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

http://hi.fi.tripod.com/timeline/timeline.htm

http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm

http://scienceworld.wolfram.com/biography/Berzelius.html

http://www.nobeliefs.com/atom.htm

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/

periodic_table/covalentbondingrev4.shtml

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/

periodic_table/atomstrucrev5.shtml

http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/

patterns/periodictablerev4.shtml

http://www.nndb.com/people/771/000091498/

http://en.wikipedia.org/wiki/J._J._Thomson

http://www.rsc.org/chemsoc/timeline/pages/1799.html

http://www.chemheritage.org/discover/online-resources/chemistry-in-

history/themes/electrochemistry/berzelius.aspx