Atomic Theory

Timeline created by rossie
  • 400

    Democritus Theory

    He discovered this in 400 BC. The Democritus Atomic Theory revolves around the atoms that are present in the atmosphere. These are about the atoms that are present in all the forms of existence; for instance, solid or liquid. The theory states that these atoms are all individually created and cannot be separated, no matter what scientific procedures are applied. The Democritus Atomic Theory is pretty much clear and the ideas are portrayed in manner that can be easily understood.
  • Antoine Lavosier

    Antoine Lavoisier is called the Father of Modern Chemistry, having discovered that water is made of hydrogen and oxygen. He also invented the analytical balance and showed that chemical elements were neither created nor destroyed, just combined into different compounds in chemical reactions. From this work follows one of the most fundamental principles of physics, the conservation of mass.
  • Law of Conservation and Mass

    States that mass is neither created nor destroyed in any ordinary chemical reaction. Or more simply, the mass of substances produced by a chemical reaction is always equal to the mass of the reacting substances.
  • John Dalton Theory

    Dalton's theory was based on the premise that the atoms of different elements could be distinguished by differences in their weights. All matter is composed of atoms. Atoms cannot be made or destroyed. All atoms of the same element are identical. Different elements have different types of atoms. Chemical reactions occur when atoms are rearranged. Compounds are formed from atoms of the constituent elements.
  • Dalton's Atomic Theory

    Elements are composed of exceptionally small particles called atoms. All atoms of a given element are identical in which they share the same size, mass and chemical properties. However, the atoms of one element are quite different from the atoms of all other elements. Compounds are composed of atoms of more than one element. In any compound, the ratio of the # of atoms of any two of the elements present is either a simple fraction or an integer. A chemical reaction can only involve combination.
  • Dmitri Mendeleev

    Mendeleev began working on his great achievement: the periodic table of the elements. By arranging all of the 63 elements then known by their atomic weights, he managed to organize them into groups possessing similar properties. Where a gap existed in the table, he predicted a new element would one day be found and deduced its properties. And he was right. Three of those elements were found during his lifetime: gallium, scandium, and germanium.
  • J.J. Thomson Theory

    He discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio. Later he estimated the value of the charge itself.
  • Cathode Ray Tube

    Physicists in the 19th century found out that if they constructed a glass tube with wires inserted in both ends, and pumped out as much of the air as they could, an electric charge passed across the tube from the wires would create a fluorescent glow. This cathode ray also became known as an ‘electron gun’.
  • Plum Pudding Atomic Model

    The Plum Pudding Model is an atom model. It is also known as the Chocolate Chip Cookie or Blueberry Muffin Model. For example, you can imagine a plum pudding wherein the pudding itself is positively charged and the plums, dotting the dough, are the negatively charged electrons.
  • Robert Millikan

    Millikan measured the charge on an electron with his oil-drop apparatus. From a perfume bottle sprayed oil or water droplets into the sample chamber. Some of the droplets fell through the pinhole. Into an area between two plates (one positive
    and one negative). This middle chamber was ionized by x-rays. Particles that did not capture any electrons fell to the bottom plate due to gravity. Particles that did capture one or more electrons were attracted to the positive upper plate and either.
  • Electron Cloud Model

    Discovery prove the conventional theory wrong of atom being the indivisible unit of matter. In 1909, Rutherford brought out the fact that the positive charge and the mass of an atom is concentrated towards the center of an atom and that the electrons orbit around the atomic center. Niels Bohr, a Danish physicist modified Rutherford’s model by proposing that the orbital of electrons is restricted to predefined orbits and that they can make a transition between the orbits on absorbing or emitting.
  • Gold Foil Experiment

    This experiment was determined to find out the structure of an atom. By this time it was discovered by J.J. Thomson that electrons are present in an atom and that they are negatively charged. So it was assumed that since an atom is neutral and electrons present are negatively charged, there should be some positive charge inside it that makes it neutral.
  • Rutherford Model

    Rutherford was forced to discard the Plum Pudding model and reasoned that the only way the alpha particles could be deflected backwards was if most of the mass in an atom was concentrated in a nucleus. He thus developed the planetary model of the atom which put all the protons in the nucleus and the electrons orbited around the nucleus like planets around the sun.
  • Ernest Rutherford

    Rutherford advanced atomic theory by suggesting a "next step" in atomic structure. We now know that atoms have a nucleus with neutrons and protons in it. Of the total mass of the atom. The electrons form up in shells in the electron cloud.
  • Bohr Planetary Model

    Bohr published a theory about the structure of the atom based on an earlier theory of Rutherford's.Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties. Bohr also described the way atoms emit radiation by suggesting that when an electron jumps from an outer orbit to an inner one, that it emi
  • Neil Bohr Theory

    Niels Bohr applies quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit.
  • Quantum Mechanical Model

    The Quantum atomic model is the most recent model of the atom. it's based on quantum mechanics (mathematical solutions of theoretical equations) quantum numbers are quantum solutions to quantum equations and are used to find the probable position and location of an electron in an atom. the first Principal quantum number identifies which energy level an electron is in.
  • Henry Moseley

    Henry Moseley published the results of his measurements of the wavelengths of the X-ray spectral lines of a number of elements which showed that the ordering of the wavelengths of the X-ray emissions of the elements coincided with the ordering of the elements by atomic number. With the discovery of isotopes of the elements, it became apparent that atomic weight was not the significant player in the periodic law as Mendeleev.
  • James Chadwick

    As they studied atomic disintegration, they kept seeing that the atomic number was less than the atomic mass. For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus were adding to the mass.
  • Erwin Schrodinger Theory

    Took the Bohr atom model one step further. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. Unlike the Bohr model, the quantum mechanical model does not define the exact path of an electron, but rather, predicts the odds of the location of the electron. This model can be portrayed as a nucleus surrounded by an electron cloud.