ATOMIC HISTORY TIMELINEBy Tyler Genereux

and Nick Faulkner-Filosa

Thales of Miletus

Thales of Miletus is regarded as one of the first scientists. Aristotle believed this was because he defined the substances of which all material objects are composed. He believed that the world started from water and that everything including land was formed by water. His theory was that water is the almighty element that it is part of everything.

620s – 540s BC

DemocritusLittle is known about the life of

Democritus because that is not what we remember him for. what we do know is that he was born in Abdera, Thrace around 460 B.C. He spent a majority of his life traveling the world in search of information. It is said that he spent several years in Egypt to study the mathematical and physical systems of the ancient schools. It is also said that a Greek philosopher by the name of Leucippus was his teacher, and brought forth the idea of Democritus‘ atomic theory.

Democritus’ theory was that all matter, including space and time, was made up of tiny particles called atoms. These atoms were able to group up to form things. He hypothesized that the characteristics of an object were determined by the shape of the atoms. Something sweet would have smooth atoms, while something sour would have sharp atoms. Democritus’ thoery was the beginning of the actual understanding of atoms and the way molecules and matter is made up.

Greece460-371 B.C

Small, spherical, solid, indivisible model

This model is one of the earliest attempts at producing a valid model of the atom. Democritus thought that atoms were simply small particles that made up everything.

Aristotle Aristotle disbelieved the theory of atoms being

of different sizes, regular geometric shapes and being in constant motion. He didn't think atoms could be in constant motion in a void. He developed the theory that all matter consisted of four elements: Earth

Air Water and Fire There were also four qualities: dryness,

hotness, coldness, and moistness. Fire was dry and hot, water was moist and cold. Each of these elements move naturally in a line to their proper place, where it will be at rest. Aristotle's theory also had two forces: conflict and harmony. Conflict was thought to cause bad things, and harmony good things. Aristotle also believed that the heavens were made of a fifth, superior element named aither. Aristotle's theory was used for almost 2000 years, until after the scientific revolution, when other theories prevailed.

384-322 BC

Isaac NewtonBorn to an uneducated

farming family in England, Isaac Newton didn’t get off to the best of starts. As a boy he didn’t do well in grammar school, and he didn’t seem to have much interest in being educated. It wasn’t until he was older when his uncle William Ayscough thought he should be prepared to enter a university. Newton entered the Trinity College of Cambridge and proceeded to excel in his studies. He then became a professor of mathematics and physics. “it was the prime age of invention,” and Newton published many works such as Principia.

Newton stated that “matter is formed of solid, impenetrable particles, ” like Democritus. Newton found the forces that bound atoms together to make molecules have an electrical neutrality. Today all molecules are known to be neutral unless they are isotopes. England

1642-1727

Coulomb

Coulomb wrote seven papers on the attraction and repulsion of opposite and like charges and developed a theory. He demonstrated an inverse square law for such forces and went on to examine perfect conductors and dielectrics. He suggested that there was no perfect dielectric, proposing that every substance has a limit above which it will conduct electricity. These fundamental papers put forward the case for action at a distance between electrical charges in a similar way as Newton's theory of gravitation was based on action at a distance between masses. 

1736-1806“It is to Borda and to Coulomb that one owes the renaissance of true physics in France, not a verbose and hypothetical physics, but that ingenious and exact physics which observes and compares all with rigour.” -Biot

Antoine Lavoisier Antoine Lavoisier was a French

chemist in the mid-seventeen hundreds and is known as one of the fathers of modern chemistry. He was an avid young learner, and was first recognized when he helped light the streets of Paris with a new form of saltpeter that he developed.

Lavoisier is known in the chemistry world for establishing the law of conservation of mass, which states: “Mass is neither created nor destroyed in an ordinary chemical reaction.” In other terms, the mass of substances produced by a chemical reaction will always equal the mass of the reactants.

1.00g carbon + 5.34g sulfur 6.34g carbon disulphide

France1743-1794

John Dalton Born and raised in Cumberland,

England, John Dalton made his living as a teacher starting at age 12. After teaching at a boarding school in Kendal, Dalton decided to take a teaching position in Manchester. In Manchester Dalton joined the Manchester Literary and philosophical society, Dalton presented his first paper on color blindness to this society. Dalton’s views on the atom actually came from his interest in meteorology. Dalton kept a daily weather record, his first published book was called Meteorological Observations.

England1766-1844

John Dalton Although Democritus was one of the

first to think of the concept of the atom, John Dalton was the man responsible for coming up with the first useful atomic theory of matter. He came upon this theory while performing an experiment with steam and asked “ how can air and water could occupy the same space?” This lead to the foundation of Daltons theory which was:

1. All matter consists of tiny particles . 2. Atoms are indestructible and

unchangeable. 3. Elements are characterized by the

mass of their atoms. 4. When elements react, their atoms

combine in simple, whole-number ratios.

Dalton was also the first to associate the idea of atoms with stoichiometry. His ideas were published in 1803.

John Daltons Atomic Model

James Clerk Maxwell One of Maxwell’s most

important discoveries was found in the year 1890 with was the Kinetic theory of gases. Using the data from experiments conducted by the scientists John Herapath, John James Waterston , James Joule, and Rundolf Clausius, Maxwell was able to come up with the first approximation of a measurement of atomic dimensions. All of this was based on the experimental data which included the viscosity, heat conduction, and diffusion in gases, coupled with mathematical data which described the collisions of large molecules and their calculated “free path” of the molecule. The free path of the molecule was discovered by Clausius, in an experiment to explain why gases didn’t diffuse as fast as their speed would indicate . And this was because of the collision of the molecules resisting the speed of transit.

Scotland 1831-1879

James Clerk Maxwell James Clerk Maxwell was born into

a middleclass Scottish family in the year 1831. His early childhood education was given by his mother, who was a dedicated Christian and tried to teach him the ways of god. She told him that there was complete harmony between the teachings of god and scientific investigation, this had a great influence on Maxwell’s work. Unfortunately Maxwell’s mother died when he was eight years old, and his father had to find a tutor for him. As he grew older, he flourished in his academics, his first scientific paper was a mathematical analysis involving the ellipse, he published this work when he was just fifteen.

James and his mother Frances

Cay

Wilhelm C. Roentgen

As a young boy Roentgen didn’t show much of an aptitude for education, instead he enjoyed observing nature as he hiked through the country forests. What he did find an aptitude for was the construction of mechanical devices. In 1862 he attended a technical school in Utecht where he was falsely accused of mocking a teacher and expelled. Roentgen found himself at the polytechnic at Zurich. He studied mechanical engineering and graduated with a Ph.D. His first work was published in 1870, which dealt with specific heats of gases.Roentgen was recognized in 1901 for the discovery of x-rays . He discovered x-rays in his lab in during the year of 1895 when he took barium platinocyanide crystals and exposed them to a crook’s, or cathode-ray discharge, tube. When exposed the crystals would become fluorescent , even when they were being shielded by some sort of cardboard or metal sheet. Finally he had his wife put her hand in the path of the radiation , a picture of her bones was produced. He named these rays of radiation “x-rays.”

Germany1845-1923

Roentgen’s X-Ray

Henri Becquerel Henry Becquerel was noted for him most

important discovery in the year 1896. Becquerel discovered the phenomenon of natural radioactivity . He found this with the help of some uranium salts he had inherited from his father, when exposed to light they would phosphoresce. When placed near a photographic plate covered in opaque paper, the plate was discovered to be fogged. This phenomenon was determined to be a property of the uranium atom. However, even when little light was exposed to the uranium it still left the silhouettes of the crystals . After a few more experiments conducted in a dark room with no light Becquerel saw that the salts were still leaving silhouettes on the paper. Becquerel then determined that the salts radiation alone was causing the silhouettes to appear, and had no influence from the sun and were not related to phosphorescence . Becquerel was awarded half of the Nobel prize for physics in 1903, while the other half was given to the Curie’s.

France1852-1908

Becquerel with his experiment

Photograph cause by uranium radiation

JJ Thomson Thomson’s most important discovery to

modern science was the discovery of the electron in 1897. Thomson made his discovery with the help of a “crooks tube.” The tube was constructed out of glass and contained two wires, one on each side of the tube. The inside of the tube was kept at a vacuum, so when current was put through a wire at one end the electricity would arc to the other side. Thomson theorized that the “cathode rays” inside the tube were actually a stream of particles smaller than the atom. This assumption was actually correct, and the small particles were electrons. He found that these particles had a charge by manipulating the beam of light with a magnet or electrical field . Thomson made a model called the “plum pudding model,” the model is what Thomson theorized the structure of the atom to look like. It was electrons surrounded by a positive jelly.

England 1856-1940

Thomson performing his experiment with the crooks tube.

Thomson’s Plum pudding model, the red exterior(pudding) is positively charged, while the electrons(plums) are negatively charged. The radius of the model was supposed to be 10^-10 meters. However, this was only a vague explanation of the electron, and failed to provide any definite answers

Ernest Rutherford

Rutherford was responsible for many discoveries in the scientific world. he discovered a new noble gas called thoron, an isotope of radon. What Rutherford is most famous for was an experiment designed to emit positively charged alpha particles through a piece of microscopically thin gold. He assumed the particles would pass right through the gold with little to no deflection angle, if the particles did have a small angle it would have been because of the small electric field that was inside the atom. When the experiment was held Rutherford observed very large reflection angles, some of the particles even shot back from where they came. From these observations Rutherford concluded that the majority of the mass of the atom, along with all of its positive charge was concentrated in a minute point in the middle of the atom, known today as the nucleus . This discovery helped with the atomic structure that we know today.

New Zealand 1871–1937

The top circle indicates what Rutherford thought was going to happen when the alpha particles passed through what he thought an atom looked like.

Rutherford’s experiment design.

Rutherford-Bohr Model

Each orbit around the nucleus represents an energy level, and electrons cannot exist in between orbits. Orbits closer to the nucleus have lower energy. If energy is added, an electron can be "excited" to jump to a higher energy level--an orbit farther from the nucleus. Eventually, though, the electron will return to its original state, and the atom will give off energy equal to the difference between the two orbits.

Niels Bohr

Bohr worked extensively on the structure of atoms. He won the Nobel Prize in 1922 for his work. Bohr studied the structure of atoms on the basis of Rutherford's discovery of the atomic nucleus. By introducing conceptions borrowed from the Quantum Theory as established by Planck he succeeded in working out and presenting a picture of atomic structure that, with later improvements (mainly as a result of Heisenberg's ideas in 1925), still fitly serves as an elucidation of the physical and chemical properties of the elements.

1885-1962

Planetary Model

The Bohr Model is used as a symbol for atomic energy. In the Bohr Model the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun.

Marie Curie She helped to discover Polonium

and Radium.To do this she and her husband took Pitchblend, which contained the radioactive element Uranium by the ton and carefully isolated the radioactive components over several years. What they found was that there were more than one radioactive element in it because they found an element that was far more radioactive than the element uranium. She got a Nobel in Physics for radioactivity. She got a Nobel in chemistry for discovering two new elements. After completing this experiment, Curie discovered that all atoms are not alike and that the theory that all atoms are structured identically should be abandoned (Dr. Reich’s Power Point)

Poland 1867-1934

Robert A. Millikan

Discovered the charge of an electron in 1910.He also proved that this quantity was a constant for all electrons thus demonstrating the atomic structure of electricity.

Millikan's Experiment

Erwin Schrodinger

Schrodinger won the Nobel Prize for Physics in 1933 for his newly discovered wave equation (The Schrodinger Equation). Schrodinger was not satisfied with the quantum condition in Bohr’s Orbit Theory and his belief that the Atomic Spectra should really be determined by a different type of equation.

Schrodinger worked with light. He experimented with the fact that light moved in waves. He didn’t agree with Niels Bohr and his philosophies about light. Schrodinger came up with his nobel prize winning “Schrodinger Wave Equation”.

1887-1961

James Chadwick In 1932, Chadwick proved the existence of

neutrons. He also used charged helium nuclei to repel the electrical forces present in the nucleus of heavy atoms and therefore is able to penetrate those forces in even the heaviest atoms. This new concept made the nuclei of other atoms vulnerable and these nuclei could now be split. In discovering this, Chadwick paved the way towrads the creation of the atomic bomb.

Chemists Bothe, Becker, Irene Joliot-Curie and husband Frederic, thought that high-energy gamma rays were emitted when alpha rays were shot at beryllium. Chadwick challenged this proposal. He knew that to cause neutral radiation to penetrate through 200mm of lead, a velocity of 50 million electron volts was necessary (alpha ray particles colliding with beryllium nuclei only produce 14million electron volts). He theorized that the beryllium rays were “neutral protons”. Through this experiment he did indeed discover the neutron (he named this neutral proton a “neutron” as well) and proved Rutherford’s prediction that there was a neutral proton correct.

1891 - 1974

Werner Heisenberg Heisenberg won the Nobel Prize

for Physics in 1932 for his Theory of Quantum Mechanics. His theory resulted in the discovery of allotropic forms of Hydrogen.

Heisenberg proposed that no experiment can tell the position and momentum at the same time. This theory was coined the “Heisenberg uncertainty principle”. This implies that when one measures the certainty of a position of a particle, the uncertainty in the momentum gets correspondingly larger (and vice versa).

1901-1976

Electron Cloud Model

Schrodinger was the chemist who came up with the electron cloud model. The model is supposed to represent where an electron could be at any given moment. The dots the dots on the outside of the nucleus are traces of where the electron was, so the traces of the electron create a cloud around the nucleus .