Robert Boyle, John Dalton, Ernest Rutherford, and Antoine Becquerel all made important contributions to atomic theory through their experiments and discoveries: 1) Boyle defined the concept of an element and overturned the idea of the four classical elements through his chemical experiments. 2) Dalton developed atomic theory by proposing atoms of different elements have unique weights and combine in fixed ratios, laying the foundation for modern chemistry. 3) Rutherford's gold foil experiment showed that atoms have a small, dense nucleus, establishing the nuclear model of the atom. 4) Becquerel accidentally discovered radioactivity by leaving uranium salts exposed in his drawer, finding they emitted radiation without exposure to light, a phenomenon further

1. Boyle, Dalton, Becquerel and Rutherford’s
contribution to Atomic Theory Research
Robert Boyle- THE FATHER OF CHEMISTRY
Background:
Jan 25, 1627 Ireland
Influenced by Galileo
Even though he is credited as the first modern chemist he was still a metallurgist.
Believed science should be rooted in experiments& experiments should consist of careful measurement.
Really helped change the way people look at chemistry and science as a whole
Boyle is best known for his work with gases and air.
Atomic Theory Contribution
develop a definition of an element
helped with "the death" of the four elements
He helped emphasize the importance of experiments and precise measurements.
In 1655 Boyle moved to Oxford where he joined a group of natural philosophers
Robert Hooke (1635-1703) entered Boyle’s employ at this time and helped him in his experiments.
They built the air-pump used to create vacuums
Which Boyle used to carried out many trials to elucidate the nature and importance of air.
Boyle demonstrated the necessity of air for combustion, for animal breathing, and for the
transmission of sound.
Prior to moving from Oxford to London in 1688, he published much influential work, including New
Experiments Physio-Mechanical, Touching the Spring of the Air and its Effects (1660) and The
Sceptical Chymist (1661).
In The Spring of The Air he described the inverse relationship between the volume of a gas and its
pressure – now known as Boyle’s Law.
Can’t have a table of the elements if you have not defined what elements are
Age 34, Boyle published The Skeptical Chymist.
overturned Aristotle’s conception of the four elements (the belief that everything was composed of
earth, air, fire and water)
Replaced it with the modern idea of an element—namely that an element is a substance that cannot
be separated into simpler components by chemical methods.
The Skeptical Chymist is recognized as the foundation-stone of modern chemistry.
Pre-Boyle The history of our theory of the atom begins in Greek about 450 B.C. A philosopher named
Leucippus began thinking about whether matter could be divided in half indefinitely. He thought that at
some point matter could not be divided any more. A pupil of Leucippus, named Democritus, took his idea
further and said that matter was made up of "atomos" or atoms which mean "unbreakable." Epicurus (341 -
270 B.C.) took up the idea of atomism and wrote books on the subject. These books did not survive, but a
Roman named Lucretius (96 - 55 B.C.) wrote a long poem "On the Nature of Things" which described the
ideas of Epicurus in great detail

2. Post-Boyle Robert Boyle (1627 - 1691) was influenced by the writings of Gassendi (1592 - 1655) who had
written about Lucretius and atomism. Robert Boyle did experiments to prove the atomism theory. Boyle
worked with gas pressures and explained the compressibility of gases on the existence of atoms. If gases
were made of atoms that were far apart and the gas was put under pressure causing the atoms to move
close together then the volume would decrease. Boyle’s experiments were hard to argue with because
other scientists could repeat his experiments and make the same observations that Boyle had made.
Proved atoms existed in gas>elements +4 > death of old 4 elements – experiments are important
John Dalton
Background:
(1766–1844)Eaglesfield, England
British chemist and physicist.
(1801) he formulated his law of partial pressures (see Dalton's law)
Best remembered for Dalton's atomic theory, (1803)
Dalton also studied colour blindness
Through studying meteorology study Dalton formed an interest in the gases of the air and their ultimate
components. This interest of gases led to Dalton’s discovery of the Atomic Theory.
Dalton was a humble man with several apparent handicaps: he was poor, he was not articulate, he was not a
skilled experimentalist, and he was colour blind. These disadvantages are a terrible problem for a chemist,
but in spite of these Dalton made his most important contribution to science called the atomic theory. The
theory consists that matter is composed of atoms of differing weights and combine in simple ratios by
weight. Dalton worked out his atomic theory during 1803-04 and developed a table of atomic weights for
elements... This theory which Dalton first advanced in 1803 is the cornerstone of modern physical science.
According to his theory, which he introduced in New System of Chemical Philosophy (1808-10; 1827), all
atoms of the same element have the same weight, and the atomic weight of each element is different.
Therefore, Dalton reasoned, atomic weight could be used to classify elements. Parts of his theory were later
proved wrong, but his ideas about atomic weight remain a key concept in chemistry and nuclear physics
Atomic Theory Contribution-Dalton's atomic theory-
All matter consists of tiny particles (atoms)
Atoms are indestructible and unchangeable
Elements are characterized by the mass of their atoms
When Elements react, their atoms combine in simple, whole-number ratios
Atoms can neither be created nor destroyed in chemical reaction.
Atomic theory was a result of his research into gases
Discovered certain gases only could be combined in certain proportions even if two different
compounds shared the same common element/ group of elements.
Led him to hypothesize that elements combine at the atomic stage in fixed ratios.
This ratio would naturally differ in compounds due to the unique atomic weights of the elements
being combined
Revolutionary idea but further experimentation by himself and others confirmed his theory.
At the time considered true for all reactions involving atoms-later corrected with the discovery of
nuclear fission and fusion, now know that this only holds true for chemical reactions.

3. Impacts
Dalton’s atomic model has been perfected over time with the research and discoveries of other
scientists.
Now know that the atom can be divided into even smaller particles and we have even discovered the
actual internal atom structure, even able to view it through modern technology.
We now know that atomic weight is a product of the structure of the atoms as well.
Until Dalton’s time the atom was only considered to a philosophical construct passed down by the
ancient Greeks
This atomic theory made possible modern chemistry and physics.
This understanding the atom helped to fuel many other discoveries such as the fundamental forces
and Einstein’s theory of relativity.
Rutherford- Father of Nuclear Physics
Background
30 August 1871,New Zealand
Returned to England (1907) to become Langworthy Professor of Physics in the University of
Manchester
Noble prize (1908),knighted in 1914, Elemented 104
In 1899, Rutherford studied the manner in which radioactive radiations penetrated sheets of aluminium. He
found that some of the radiation could be stopped by 1/500 of a centimetre of aluminium, while the rest
required a considerably thicker sheet to be stopped. Rutherford called the first type of radiation alpha rays,
from the first letter of the Greek alphabet, and the second type beta rays, from the second letter. A third
type of radiation, which was the most penetrating of all, was discovered in 1900 by the French physicist Paul
Ulrich Villard (1860 - 1934), and was called gamma rays, from the third letter of the Greek alphabet.
Rutherford thought that the alpha particle, which had a mass 7000 times greater than the electron, would
be good for studying the structure of the atom. In what has now become the famous Gold Foil experiment,.
Atomic Theory Contribution
Ernest Rutherford's great contribution to atomic theory was to show what happens to an element during
radioactive decay. This enabled him to construct the first nuclear model of the atom, a cornerstone of
present-day physics
(1911) beams of particles to explore the structure of matter
Used the decay of radioactive elements to produce these beams (no particle accelerator in those
days)
Hans Geiger and Ernest Marsden (students of ER) asked to fire Alpha Particles at some thin gold foil
If the nucleus was more of a blob (as thought) they expected the particles to pass right through
This happened to most hwr 1/8000 bounced back
2yrs later, after much though over these resulted, ER realised for the alpha particles to bounce back,
it must hit something small dense
New model of Atom- like solar system Mass concentrated at centre & elections orbits
Nowadays this is incorrect and QP tells us we can’t pinpoint the exact location of the electrons
Can predict they reside in shells around the nucleus

4. Rutherford’s alpha scatting experiment was direct and simple
Show the nature of the atomic model by the way the alpha particles bounce- he worked out where the positive
charge is
Rutherford came to the conclusion: most of the atom is empty space w/ very small nucleus of great
mass.
1932- ER continued experimenting and firing particles at different targets
James Chadwick (partners) found 2 particles in the nucleus +Protons & =neutrons
Antoine Henri Becquerel
Background
15 Dec 1852, Paris
French physicist
awarded half the 1903 Nobel Prize in Physics
Followed in father’s footsteps (solar radiation)
Discovery of radioactivity
Atomic Theory Contribution
(Early career) research physicist, Becquerel developed laws of radiation of light from
phosphorescent substances.
Attending a lecture on the discovery of "X-rays," Becquerel's attention captured by the mention of a
fluoroscope(father invented)
After, began his own study of X-rays, reproducing Wilhelm Röntgen's experiments.
Suspicion that fluorescent materials might emit some of these X-rays.
(1896) began working with crystals of a uranium compound (potassium uranyl sulfate), which, after
exposure to sunlight, emitted fluorescent light. To determine whether X-rays were being emitted by
the compound, he prepared a photographic plate for use after exposing a sample of the uranium salt
to the Sun.
A cloudy period ensued, during which no sunlight was
available.
He wrapped the crystals and a copper cross in a black cloth
with the photosensitive plate and put them in a drawer,
intending to retrieve them later.
Quite a number of rainy days followed, with no sunlight.
He finally removed the plate from the drawer and developed
it, expecting to see some faint evidence of emission of
radiation. To his surprise, the photographic plate revealed a
distinct image of the copper cross, evidence that strong
radiation must have come from the uranium compound
itself.
Accidentally discovered the phenomenon that came to be known as "radioactivity."
Describing his method to the French Academy of Sciences on January 24, 1896, he said,

5. One wraps a Lumière photographic plate with a bromide emulsion in two sheets of very thick black
paper, such that the plate does not become clouded upon being exposed to the sun for a day. One places
on the sheet of paper, on the outside, a slab of the phosphorescent substance, and one exposes the
whole to the sun for several hours. When one then develops the photographic plate, one recognizes that
the silhouette of the phosphorescent substance appears in black on the negative. If one places between
the phosphorescent substance and the paper a piece of money or a metal screen pierced with a cut-out
design, one sees the image of these objects appear on the negative. … One must conclude from these
experiments that the phosphorescent substance in question emits rays which pass through the opaque
paper and reduces silver salts.
Becquerel was Marie Curie's doctoral adviser and collaborated with Pierre and Marie Curie in their
studies of radioactivity.
W/ Becquerel's support, the Curies published their findings on radium in the journal of the Academy
of Science in France.
Marie Curie used the term "Becquerel rays" referring to the radiation discovered by Becquerel & was
the first to use the term "radioactivity" to describe both Becquerel rays & the radiation that she &
Pierre discovered emanating from radium.
Based on his research on radiation phenomena, Becquerel declared (1899); the rays could be
deflected by a magnetic field.
observation suggested that at some of the radiation was composed of electrically charged particles.
In 1900, he was clearly committed to the idea that the radiation had to include particles of negative
charge—just like the cathode rays discovered by J.J. Thompson.
In 1901, Becquerel identified uranium as the component of his experimental compound that emitted
the radiation. He published ½ dozen papers exploring the phenomenon of radioactivity before
turning his attention to other interests.
He placed sample uranium and a photographic plate in a black bag into a drawer while waiting for clear
weather to expose the uranium to sunlight for an experiment. When he developed the plate a couple
days later, he found an image of the uranium rocks demonstrating the existence of radioactivity.
Sources
https://sites.google.com/site/robertboyletheskepticalchemist/atomic-theory-contribution
http://www.rcs.k12.va.us/chemistrynhs/advanced/01_adv_atomic/advanced_atomic.htm
http://understandingscience.ucc.ie/pages/sci_robertboyle.htm
http://www.universetoday.com/38169/john-daltons-atomic-model/#ixzz24B7xhUmo
http://www.rcs.k12.va.us/chemistrynhs/advanced/01_adv_atomic/advanced_atomic.htm
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.htm
http://static.newworldencyclopedia.org/1/1e/Becquerel_plate.jpgl
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