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Atomic Theory Timeline

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BC: A Recent Societal Issue About the Atom http://news.discovery.com/tech/lhc-atom-smasher-discovery.html I can agree with this article, because in the past there has been many phenomenons with the atom. Since there were some proton particles that were intimately linked in a way not seen before in proton collisions, there will be an impact in science once scientists know why the particles are linked, leading to other phenomenons. I don't think that the discovery will lead to impacting the society, but it will definetly impact the development of the atomic theory.

FC: Atomic Theory Timeline By: Ruth Yeh A Timeline of the History of the Deveopment of the Atomic Theory.

1: Democritus (460-370 B.C): He was the first Greek philosopher to propose the idea that matter was not infinitely divisible. He believed that matter was made of tiny individual particles called atoms. | Democritus's Ideas: Matter is composed of empty space through which atoms move. Atoms are solid, homogeneous, indestructible, and indivisible. Different kinds of atoms have different sizes and shapes. The differing properties of matter are due to the size, shape, and movement of atoms. Apparent changes in matter result from changes in the groupings of atoms and not from changes in the atoms themselves. He was unable to conduct controlled experiments and did not have a model of an atom.

2: John Dalton (1766-1844): The work done by the English schoolteacher marked the beginning of the development of modern atomic theory. Dalton's Atomic Theory (1803): All matter is made of indivisible atoms. All atoms of the same elements are the same. Atoms of different elements are different. Atoms combine in simple whole number ratios to form compounds. Dalton studied numeorus chemical reactions, making careful observations and measurements on the way. He was able to accurately determine the mass ratios of the elements involved in the reactions. He also based his research on the work of two scientists, Lavoisier and Proust. | Dalton's Model of an Atom (Indivisible)

3: Lavoisier (1788): Law of Conservation of Mass: Matter can't be created or destroyed, only rearranged. Experiment: He carefully weighed the reactants and products in a chemical reaction, and later showed that, although matter can change its state in a chemical reaction, the total mass of matter is the same at the end as at the beginning of every chemical change He did not have a model of an atom. | Proust (1794): Law of Definite Proportions: A pure substance always contains the same elements in the same porpotion by mass. Ex: H20 water Experiment: He experimented by reacting different elements such as iron and copper with oxygen finding that oxygen's composition was always one of two. He does not have a model of an atom.

4: Gay-Lussac (1778-1850): Law of Combining Volumes: At constant temperature and pressure, volumes of reacting gases and gaseous products are in the ratio of small whole numbers. (1804) Experiment: He performed experiments on the ratio of the volumes of gases involved in a chemical reaction. studied the volume of gases consumed or produced in a chemical reaction because he was interested in the reaction between hydrogen and oxygen to form water. He did not have a model of an atom.

5: Avogadro (1776-1856): An Italian savant who was most known for his contributions to molecular theory, as known as Avogadro's Hypothesis (1811), which is the hypothesis that equal volumes of gases, under the same condition have the same number of particles. | This number (known as Avogadro's number) was later determined to be 6.002 x 10 to the 23rd power. This number of particles is defined as one mole. Experiment: He studied the reaction between Oxygen and Hydrogen, and saw that there were no particles left over. He did not have a model of an atom.

6: Henri Becquerel (1852-1905): The French physicist discovered that uranium ores emit radiation resembling X-rays and that it exposed films. | Experiment: Becquerel decided to investigate whether there was any connection between X-rays and naturally occurring phosphorescence. Later, Becquerel showed that the rays emitted by uranium, which for a long time were named after their discoverer, caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields. He did not have a model of an atom.

7: J.J. Thomson (1856-1940): A English physicist who began a series of cathode ray tube experiments, leading to the discovery of protons and electrons. He determined the charge to mass ratio of an electron. | Experiment: By carefully measuring the effect of both magnetic and electric fields on a cathode ray, thomson was able to determine the charge-to-mass ratio of the charged partice. After comparing that ratio with other known ratios, he concluded that the mass of the charged particle is much less than that of a hydrogen atom, the lightest known atom. This meant that atoms were divisible into smaller subatomic particles (1897). He did not have a model of an atom. Thomson's model of an atom. (Plum Pudding/Cookie)

8: Marie and Pierre Curie: They were the first to use the term "radioactivity." (1900) Fun Fact: Marie saw her husband die after being run over by a wagon. | Experiment: They isolated two new elements, polonium and radium, from uranium. They noticed that these radioactive substances ionized air, caused phosphorescent substances to glow, | killed bacteria and small organisms, and increased the temperature of the air surrounding the substance. They did not have a model of an atom.

9: Experiment: He researched on the amount of light needed to produce heat, and discovered that little amount of heat brightens a substance. He put forward the hypothesis that light is a stream of energy and energy emitted in specific amounts or quanta. According to him, different levels contain different amounts of energy. According to Planck, the energy associated with a quantum of radiation is proportional to the frequency of radiation, and the constant of proportionality. E=hu He didn't have a model of an atom | Max Planck (1858-1917): A German physicist who is known as the founder of the quantum theory (1900), which is the theory that energy is not emitted contiuously but in small packets called quanta.

10: Albert Einstien (1879-1955): The German-born physicist had been studying the relationship between energy and mass. His famous equation: 2 E=mc | Which shows that a small amount of mass can be converted into tremendous amounts of energy during a nuclear reaction (1905). Experiment: He did not do experiments but by actually working them out mathmatically. He does not have a model of an atom | The Photoelectric Effect: a phenomenon studied in the early 1900's. The wave theory of light could not explain this effect. Einstien suggested the idea that light also has a particle nature when he successfully explained the photoelectric effect, when light of a certain frequency shines a metal and electrons are emitted.

11: Ernest Rutherford (1871-1937): In 1911, Rutherford became interested in studying how positively charged alpha particles interacted with solid matter or the radiation emitted from these substances. Rutherford's model of an atom. (Nuclear) | He led another famous experiment, the "gold foil experiment". 1. Gold foil bombarded with alpha particles. 2. Most particles passed through (atom is mostly empty spaced) 3. Some alpha particles were deflected.

12: Robert Millikan (1868-1953): An American physicist who determined the charge of an electron. Experiment: He performed a classic experiment called the "oil drop experiment" (1911) to determine the charge on the electron. 1. Sprayed oil mist into chamber, electrons became droplets. 2. Oil falls through chamber due to gravity 3. Charge on plates adjusted to off set gravity and suspend drop. 4. Charge on drops calculated (He used Thomson's charge to mass ratio to calculate the charge on the electron. He did not have a model of an atom.

13: Henry Mosely (1887-1915): Mosely used X-ray experiments to discover the atomic number of an element. | Experiment: In 1913, by using X-ray spectra obtained by diffraction in crystals, he found a systematic relation between wavelength and atomic number, Moseley's law. Wavelengths of the X-rays emitted depended on the metal being used. Wavelength unique to the element depends on the number of protons in the element. He did not have a model of an atom.

14: Niels Bohr (1885-1962): The Danish physicist and a assistant of Rutherford's, improved the atomic model by attempting to answer the queston of why electrons are not pulled into the nucleus (1913). 1. e- travel in definite energy levels without radiating energy 2. e- in each orbit have certain amounts of energy. 3. energy increases as distance from the nucleus increases. 4. e- loses energy only by dropping to lower energy levels. Experiment: He concluded that accelerating electrons means they are emitting radiation and therefore losing energy and would eventually spiral in motion toward the nucleus and collapse. Bohr’s insight was that he declared an electron could orbit the nucleus but only in discrete orbits which didn’t emit radiation. (Planetary) | <------ Bohr's model of an atom | Bohr also discoved the Aufbau Principle(1920), along with Pauli. The priniciple states that electrons "bulid up" in respect to the nucleus and other electrons.

15: Louis de Broglie (1892-1987): He was a French physicist who hypothesized (1923) if waves can behave like particles, then particles can behave like waves. (wave-particle duality). | Experiment: DeBroglie did not perform an experiment, but later in 1927, two physicists Clinton Davisson and Lester Germer. They performed an experiment where they fired electrons at a crystalline nickel target. The resulting diffraction pattern matched the predictions of the de Broglie wavelength. He did not have a model of the atom.

16: Wolfgang Pauli (1900-1958): A Austrian physicist who recieved a Nobel Prize for his priniciple, Pauli's Exclusion Principle (1925). It states that no two electrons in the same atom can have the same set of 4 quantum numbers. Along with Bohr, he discovered the Aufbau Principle (1920), which is used to determine the electron configuration of an atom. The principle poses a process in which electrons keep adding on, going to their most stable condition in respect to the nucleus and the electrons already there. He did not perform an experiment and did not have a model of an atom.

17: Erwin Schrodinger (1887-1961): The Austrian physicist came up with Schrodinger's Wave Equation (1926): treat electrons as a wave; develped an equation used to determine the probability of where the electrons could be located. Schrodinger also discovered thed the quantum model of the atom. There was no experiment performed . | Schrodinger's model of an atom (Quantum model)

18: Werner Heisenberg (1901-1976): A German physicist who made important contributions to quantum mechanics, and most known for Heisenberg's Uncertainty Principle (1926): it is impossible to know both the position and velocity of an electron at the same time. He did not perform a experiment and did not have a model of an atom.

19: He was the creator of Hund's Rule (1927): "fair share"; each orbital in a sublevel must have one electron first before any orbital in the sublevel gets a second. | Friedrich Hund (1986-1997): A German physicist known for his work on atoms and molecules. | He did not perform an experiment and did not have a model of the atom.

20: James Chadwick (1891-1974): He discovered the third subatomic particle, the neutron. (1937). Experiment: He bombarded beryllium alpha particles to produce carbon and high energy neutrons. He did not have a model of a atom.

21: Glenn Seaborg (1912-1999): He contributed to the discovery and isolation of ten elements, and developed the actinide concept, which led to the current arrangement of the actinoid series in the periodic table (1945-1974) | Experiment: Although he did not perform an experiment, he researched using the the large amount of information assembled in his laboratory which has made it possible to predict the radioactive characteristics of many isotopes of elements still to be found. He does not have a model of an atom.

22: Enrico Fermi (1901-1954): The Italian-American physicist was most known for his work on the first nuclear reactor. He is frequently referred to as "Father of the Nuclear Bomb". | Experiment: The experiment of the first nuclear reactor was a pile of graphite bricks and uranium fuel under the Stagg Field in University of Chicago, in which every step had been carefully planned, every calculation meticulously done by him He did not have a model of an atom.

23: Development of the Atomic Theory The existence of atoms started more than two thousand years ago, and the discovery of new information about atoms is still going on to this day. Democritus was the first to hypothesize that matter is made up of atoms and is indivisible. The thing about timelines is that you get to see the changes and the fixes that the atomic theory went through. The model of an atom started to be an unbreakable particle, and then it changed to the complexity of Shrodinger's quantum model, which has many orbitals, made up of spinning electrons, a positive nucleus, and neutrons. The coming together of many physicists, mathmeticians, and even a schoolteacher and philosopher, they made up parts of the atomic theory. This leads to other people of different backgrounds to have a foundation to continue the atomic theory. So far there has not been a new model of an atom since Shrodinger's model.

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  • Title: Atomic Theory Timeline
  • A Timeline of the History of the Development of the Atomic Theory
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