Download John Dalton

John Dalton
By Tucker Hopkins and Charlotte Boghossian
John Dalton, born in England in 1766, was best known for his advances in atomic theory. Dalton was a
teacher for much of his career, working in meteorology and atomic theory in addition to teaching. His first
major breakthrough was the discovery of Dalton’s Law, which explained that the pressure of a mixture of gases
is the same as the sum of the individual pressures of each gas. Dalton was the first to publish a table of atomic
weights, discovering the weight of six atoms: hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus. His
discoveries in this area led many others to create and contribute to the periodic table. Finally Dalton’s atomic
theory is shown in the following postulates:
-The atoms of a given element are different from those of any other element; the atoms of different
elements can be distinguished from one another by their respective relative atomic weights.
-All atoms of a given element are identical.
-Atoms of one element can combine with atoms of other elements to form chemical compounds; a
given compound always has the same relative numbers of types of atoms.
-Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process; a
chemical reaction simply changes the way atoms are grouped together.
-Elements are made of tiny particles called atoms.
These laws were Dalton’s largest and most famous contribution to the study of the atom at the time and
are still widely accepted. He began the modern era of chemistry through these discoveries as well as in his
mistakes. His definition of the atom as the smallest particle led future scientists to disprove this and discover
electrons, protons and neutrons.
Marie Curie & Henri Becquerel by Devin and Lexie
Marie Curie and Henri Becquerel were essential contributors to the discovery and understanding of
radioactivity. Radioactivity is a measure of the particles emitted from an atom’s nucleus as a result of nuclear
instability. At the time of Curie and Becquerel, little was known about the atom other than that the atom was
thought to be the smallest particle. Becquerel researched the plane polarization of light, the phenomenon of
phosphoresce, and crystals’ absorption of light. His research on phosphoresce helped him uncover new
properties of the uranium atom. Becquerel discovered radioactivity by observing that under radiation, uranium
glowed, representing light energy being emitted from the uranium atoms. Marie Curie, influenced by
Becquerel’s discoveries, went on to prove that radioactivity is an atomic property by using an electrometer to
measure electrical currents of uranium in several different physical states. With her husband, she found that
radium’s ability to burn flesh could be used to aid in cancer treatment.
The discoveries and experiments of Curie and Becquerel greatly enriched the knowledge of the atom.
Their research on radioactivity was crucial to the discovery of subatomic particles, as well as the physical
structure of an atom.
JJ Thomson by Grace and Elena
JJ Thomson, a 19th century physicist and chemist laid the foundation for groundbreaking discoveries
regarding the atomic structure. He published several works, most notably “The Conduction of Electricity
Through Gases” in 1903. Before his time, atoms were thought to be indivisible matter. There was little
knowledge about the make up of an atom. He conducted multiple experiments concerning the charges of
particles in cathode rays. These experiments led to his discovery that atoms are in fact divisible, and that they
contain negatively charged particles, electrons. Thomson further developed an image of the internal structure of
an atom. He claimed there were both negatively and positively charged particles scattered randomly in an atom.
This inaccurate concept is referred to now as “plum pudding.” Thomson also concluded that Hydrogen was the
lightest element, and that it had only one electron per proton. Thomson’s discoveries proved crucial, and
influenced later conclusions of the atom’s true structure.
Ernest Rutherford and James Chadwick by Marcelo and Sachin
Sir Ernest Rutherford and his associate Sir James Chadwick laid the foundation for the modern
perception of the atom. Rutherford conducted the Gold Foil Experiment in 1909, which led him to prove that
the electrons orbit around the nucleus of the atom and create a completely new and original atomic model in
1911. Chadwick was the first to discover the neutrally charged particle, the neutron, in his experiment with
beryllium in 1932. Their findings uncovered the mysteries of the sub-atomic particles and contributed greatly
to the discoveries of scientists of the next generation.
Niels Bohr by Marco and Dan
Niels Bohr was a half Jewish half Danish physicist born in Denmark on October 7, 1885. He grew up
leading a normal life with a Jewish mother of rich descent, and a professor for a father. He attended and
graduated from both the University of Copenhagen as well as Manchester University. Attending these
universities he was able to study under two great physicists Ernest Rutherford and Christian Christiansen. Under
their instruction, and from working alongside with some of the greatest physicists of that era, Bohr was able to
truly flourish from his studies, and be revered as a respectable physicist. After graduating Bohr went on to
conduct some experiments under J.J. Thomson at Trinity College, after a couple of years or so he moved on
from his mentor to then conduct his own. He went on to find his own assistant, Werner Heisenberg, and began
his own experiments. His first accomplishment was his publication of the model of an atom in 1913. Bohr
introduced for the first time the theory that the electrons of an atom actually have specific orbits around the
nucleus, for which he received the Noble Prize. He was able to prove this theory through his experiments on
observing the specific wavelengths produced when exciting for example, hydrogen or helium. Bohr also went
on to discover what is referred to as the correspondence principle. Basically Bohr was able to find a way to
connect, convert, Quantum Mechanics to Classical Mechanics. This was unheard of before Bohr, he was able to
link what used to be two opposite fields together, which was a ground breaking discovery in science. In the final
portion of his life he was forced to flee his homeland in fear of being killed by the Nazi’s. After escaping he
spent his time on the Manhattan project, under his new identity (for security reasons) Nicholas Baker, where he
along with other physicists discovered that if one fired a neutron into the nucleus of Uranium 235 the atom
would split into Ba and Kr and some scattered neutrons, this was discovered and named by Bohr as slowneutron fission. When slow-neutron fission occurred it would release massive amounts of energy, and this
energy was highly destructive if massive amounts of uranium atoms where split simultaneously. He then used
this information to help the U.S. create the uranium bomb helping it become the superpower it is today. These
strides he made in science is what made Niels Bohr one of the greatest physicist to ever live.
DeBroglie, Heisenberg, and Schrödinger by Braden, Maggie, and Julianna
Quantum Mechanics is a method of calculating the probability that a particle will be in a given place, and how
those probabilities change over time. Our scientists revolutionized science by developing the main principles of
quantum mechanics, and applying them to the atom. Louis De Broglie discovered that electrons are able to
move in waves like light. He then created an equation ( =h/p) which calculated the nature of a standing wave.
Around the same time Werner Heisenberg created matrix mechanics explaining how energy is not continuous
and that electrons need a discrete or specific amount of energy to jump energy levels. He then created his
uncertainty principle, which stated that it is impossible to calculate both the exact velocity and location of an
electron. Then, Erwin Schrödinger united both of these scientists' ideas to develop his own equation. This
provided a simple way of calculating the exact velocity of an electron (or any other particle) and the probability
that the electron (or particle) will be in a certain region at a certain time.