Chemistry

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Chemistry

• An Atomic Model of Matter

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Periodic Table PunsIn your lab book and using
the periodic table of elements, answer the
following periodic table puns.

• What do you do in a play?
• What do you do to a wrinkled shirt?
• Tasty part of your mouth.
• Someone who likes to start fires.
• Supermans weakness.
• Your brother or mine.
• Extinct.
• Imitation diamond.

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• Matter is anything that has mass and volume.
• The basic building blocks of matter are atoms.
• For more than 2400 years, philosophers and
  scientists have tried to determine the
  composition of matter by using a variety of
  experiments and observations.

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• Because atoms could not be seen until recently,
  researchers relied on observations of how matter
  behaves.
• From early Greek to present day atomic theory,
  scientists have built on and modified existing
  models of the atom.

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Time Line of the Atomic Model

• Over 2400 Years Ago Democritus, a Greek
  philosopher, theorized the existence of the atom,
  the smallest particle of matter
• Early 1800s John Dalton did experiments that
  led to the acceptance of the idea of atoms. His
  theory stated that all matter is made of
  indivisible particles, or atoms.

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• 1897 JJ Thompson discovered the electron,
  proving that the atom is divisible into smaller
  particles. Thompsons model pictured the atom as
  being made of a positively charged, pudding-like
  material throughout, which negatively charged
  electrons were scattered.
• 1908 Ernest Rutherfords experiments led him to
  propose an atomic model that states that an atom
  has a small, dense, positively charged nucleus
  surrounded by negatively charged electrons

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• 1913 Niels Bohr proposed that the atoms
  electrons move in definite orbits, or energy
  levels, around the nucleus.
• Today The atomic model is based on the models
  of Rutherford and Bohr, and on the principles of
  wave mechanics. According to the theory of wave
  mechanics, electrons do not move about an atom in
  definite orbits. The exact location of an
  electron in an atom is impossible to determine.

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Modern Atomic Model

• An atom has a small positively charged nucleus
  surrounded by a large region in which there are
  enough electrons to make the atom neutral.

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The Nucleus

• The nucleus is the center of the atom.
• The nucleus is made up of protons and neutrons.

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Protons

• Protons have a positive charge.
• All protons are identical, regardless of the
  element in which they are found.
• A proton has a mass of 1 amu (To get an idea of
  how small an amu is, imagine the number 6
  followed by 23 zeros. That is how many protons
  it would take to equal a mass of just one gram.)

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Neutrons

• Neutrons are electrically neutral (it has no
  charge).
• Like protons, all neutrons are identical.
• A neutron has slightly more mass than a proton,
  but the mass of a neutron is stell considered to
  be 1 amu.

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Atomic Number

• The number of protons in the nucleus of an atom
  is the atomic number.
• The atomic number identifies the element.
• All hydrogen atoms and only hydrogen atoms
  have 1 proton and an atomic number of 1.
• Carbon atoms have 6 protons and an atomic number
  of 6.
• How many protons does oxygen, atomic 8 have?
  Uranium, atomic number 92? Nitrogen, atomic
  number 7?

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Mass Number and Isotopes

• The mass number of an atom is the sum of the
  protons and neutrons in its nucleus.
• Isotopes are atoms of the same element that have
  the same number of protons, but a different
  number of neutrons

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Electrons

• Electrons have a negative charge.
• Electrons have a mass of 1/1836 amu.
• Within the electron cloud, electrons are arranged
  in energy levels.
• The valence number of an element is related to
  the electrons in the outermost energy level of an
  atom of that element. It is these electrons that
  are involved in the chemical combining of
  elements to form compounds.

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Energy Levels

• Not all energy levels hold the same number of
  electrons.
• The k-shell only holds two electrons.
• The l-shell only holds eight electrons.
• The m-shell only holds eight electrons (for the
  first eighteen elements). The m-shell can
  actually hold up to 18 electrons as you move
  farther along the periodic table.
• The maximum number of electrons you will find in
  any energy level is 32.