Models of the Atom

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  • Models of the Atom

    1. 1. Models of the Atom SNC1D Grade 9 Science
    2. 2. Dalton Model • Modern atomic theory began to take shape in the early 1800s • John Dalton (1766-1844) considered the idea that each different kind of element is composed of a different kind of atom
    3. 3. Dalton Model • Dalton imagined that all atoms were small spheres that could vary in size, mass or colour • Different atoms would have different properties • All the atoms of an element have identical properties such as size and mass
    4. 4. Thomson Model• J.J. Thomson (1856-1940) researched the idea that atoms might be made from a combination of particles• Thomson used cathode ray tubes to produce streams of negatively charged particles (later named electrons)
    5. 5. Thomson Model• Electrons are now understood to be negatively charged particles in atoms.• Because all of the elements that Thomson tested produced electrons, he reasoned that atoms of all elements must contain electrons
    6. 6. Thomson Model • Because Thomson knew that atoms have no overall charge, he reasoned that atoms must also contain positive charges. • Thomson’s model is commonly referred to as the “plum pudding” model
    7. 7. Rutherford Model • Rutherford (1871-1937) conducted an experiment where he shot positively charged particles at a very thin sheet of gold foil
    8. 8. Rutherford Model
    9. 9. Rutherford Model • Most of the positive particles went right through the foil, however, about 1 in 10,000 positive particles bounced back • These particles had been deflected by something very massive and positively charged • Rutherford had discovered the nucleus - the centre of the atom
    10. 10. Rutherford Model • The nucleus is a tiny positively charged part of the atom that contains most of the atom’s mass • Rutherford calculated that the size of the nucleus compared to the rest of the atom was like the size of a single green pea compared to an entire football field!
    11. 11. Rutherford Model • Based on his gold foil experiment, Rutherford revised the atomic model
    12. 12. Chadwick Model • Chadwick (1871-1974) was a student of Rutherford who refined the concept of the nucleus • He discovered that the nucleus contains neutral particles as well as positive particles
    13. 13. Chadwick Model • The neutral particles in the nucleus of the atom are called neutrons • The positively charged particles are called protons • Protons and neutrons have approximately the same mass, however neutrons do not have an electrical charge
    14. 14. Bohr Model • Bohr (1885-1962) transformed the model of the atom into one that is commonly used today • His model shows how electrons are arranged in different elements
    15. 15. Bohr Model • Bohr suggested that electrons surround the nucleus in specific energy levels called “shells” • He discovered that electrons jump between these shells by gaining or losing energy
    16. 16. Bohr Model • Each shell can only contain a specific number of electrons • The first shell can contain a maximum of 2 electrons • The second and third shells can contain a maximum of 8 electrons each
    17. 17. Quantum Mechanical Model • The quantum mechanical model is the most advanced and accurate model of the atom, used today by chemists and physicists • In this model, electrons do not exist as tiny points inside the atom, but instead surround the nucleus in a form resembling a cloud
    18. 18. Quantum Mechanical Model

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