4.3 The Atom

4.3 The Atom

  • The elements on the periodic table are made of atoms.
    • You are tearing a piece of foil into smaller pieces.
    • Imagine if you have a small piece that can't be divided.
    • You would have a single atom of aluminum.
  • The idea of an atom is new.
    • The atomic theory proposed that atoms were responsible for the combinations of elements found in compounds.
  • All matter is made up of small particles.
  • The atoms of an element are the same as the atoms of other elements.
  • The elements combine to form compounds.
    • The atoms of compound are always made up of the same kinds of atoms and the aluminum is always the same.
  • A chemical reaction involves rearranging atoms.
  • During a chemical reaction, atoms are not created or destroyed.
  • The basis of current atomic theory was formed by the atomic theory of Dalton.
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  • Although atoms are the building blocks of everything we see around us, we can't see them with the naked eye.
    • When billions and billions of atoms are packed together, the characteristics of each atom are added to those of the next until we can see the characteristics we associate with the element.
    • A small piece of gold has many gold atoms.
  • The gold atoms have electrical charges.
  • An electrical charge can either be positive or negative.
    • Experiments show that charges repel each other.
    • Why is a microscope with high magnification charges that build up on the hair and brush the same thing?
  • Opposite or unlike charges attract.
  • Thomson realized that the particles in Negative charges must be negatively charged because the rays were attracted to a positively charged electrode.
  • The negatively charged rays are attracted to the positive electrode.
  • Thomson proposed a model for the atom in which the electrons and Negative electron "plums" were randomly distributed in a positively charged cloud like plums in a pudding.
    • Ernest Rutherford worked with Thomson to test the model.
    • Positively charged particles were aimed at a thin sheet of gold.
  • The particles would travel through the gold foil if the Thomson model was correct.
    • Some of the particles went back in the opposite direction after they passed through the gold foil.
    • It was as if he had shot a cannonball at a piece of tissue paper, and it bounced back at him.
  • The space surrounding the atom is occupied by electrons.
  • Positive particles aim at gold foil.
  • Elements and atoms came near this positive center.
    • The nucleus of a football stadium is about the size of a golf ball.
  • The nucleus was heavier than the protons, so scientists looked for another particle.
  • Most of the mass in an atom is packed into the tiny volume of the nucleus.
    • The electrons surround the nucleus and account for the large volume of the atom.
  • The things you see are larger than the particles that make up the universe.
    • One protons has a mass of about the same as the other.
    • The mass of the electron is less than that of a protons or a neutron.
    • The mass of a carbon atom is defined as one-twelfth of the mass.
  • The small electron mass is usually ignored in atomic mass calculations.
  • There are three protons and four neutrons in the nucleus.
  • An electron is heavier than a protons.
  • An electron is attracted to something.
  • The nucleus has all the elements of an atom.
  • An electron is attracted to a particle.