Atoms and the Periodic Table - DOC

Document Sample
Atoms and the Periodic Table - DOC Powered By Docstoc
                 4.1- Early Ideas About Matter
  The ancient Greeks tried to explain matter, but the scientific
   study of the atom began with John Dalton in the early 1800s.
  Early Greek Philosophers concluded that matter was
   composed of things such as earth, water, air and fire; but they
   lacked methods available to test their validity.
460-370 B.C.                 Matter is composed
Democritus                     of atoms, which
                               move through empty
                              Atoms are solid,
                               indestructible, and
                              Different kinds of
                               atoms have different
                               sizes and shapes.
                              Size, shape, and
                               movement of atoms
                             determine the
                             properties of matter.
382-322 B.C.  Aristotle    Empty space cannot
                            Matter is made of
                             earth, fire, air and
1766-1844  Dalton          Matter is composed
                             of extremely small
                             particles called
                            Atoms are indivisible
                             and indestructible.*
                            Atoms of a given
                             element are identical
                             in size, mass, and
                             chemical properties.*
                            Atoms of a specific
                             element are different
                             from those of another
                             Different atoms
                              combine in simple
                              whole-number ratios
                              to form compounds.
                             In a chemical
                              reaction, atoms are
                              separated combined
                              or rearranged.

Conservation of Mass  mass cannot be created nor destroyed.
              4.2- Defining the Atom- Student Notes
Objective: An atom is made of a nucleus containing protons and

neutrons; electrons move around the nucleus.

Atom- is the smallest particle of an element that retain the

properties of that element.

What is an atom like?

Experiments that characterized the electron

   The Cathode-Ray tube

      o What is a cathode-ray tube?

      o How were cathode-rays discovered?

      o What invention is based on the cathode-ray discovery?

      o Cathode-rays have what charge?

      o What century were these discoveries made?

      o How did they determine that the cathode-ray must be

         present in all forms of matter?
  Mass and charge of the electron

     o When, where and who began experiments to determine

       the charge-to-mass ratio of the charged particle?

     o What part of Daltons Atomic Theory was incorrect?

     o Describe the oil-drop experiment.

     o What did Millikan notice about the increase in drop size?

     o How many coulombs does a single electron carry?

Atomic Models

  The plum pudding model

     o What major concern did scientists have about matter once

     they determined the charge of an electron is negative?

  The Nucleus/ Rutherford’s model

     o An alpha particle has what charge?

     o Describe the Rutherford experiment and what the scientist

     were looking for.

     o What part of the atom holds the major of its mass?
      o Why did scientists continue to search for other subatomic

      particles after the discovery of the proton?

Copy Table 4.3 into your notes.
                         4.3 How Atoms Differ

Review: Atoms
All matter is made of atoms.
Atomic Theory states that all matter is made of atoms.
Atom = smallest unit of an element that retains all the properties of
that element.
Three subatomic particles of an atom:
                Charge       Location     Relative       Actual
                                          Mass           Mass (g)
Proton          +1           Nucleus      1              9.11 x 10-28
Neutron         0            Nucleus      1              1.673 x 10-

Electron        -1           Outside      1/1840         1.673 x 10-

Atomic Number
Atomic Number = number of protons in an atom
Because all atoms are neutral atomic number = # of protons = # of
Examples: Practice Problems pg 116 #12-15
Isotopes and Mass Number
Isotope = atoms of the same element that have different numbers
of neutrons.
Atom mass or Mass # = # of protons and neutrons
Examples: Practice Problems pg 118 #16
Mass of Atoms
Atomic mass unit ~ mass of one proton or neutron = 1/12 the mass
of a carbon-12 atom. (Carbon is the atomic standard that all atoms
are compared to)
Atomic mass = weighted average of the masses of all the isotopes
of an element.

Calculating average atomic mass of copper-63 at 69% and copper-
65 at 31%.
    (63 amu * 0.69) + (65 amu * 0.31) = 63.62 amu
Practice Problems pg 121 #18-19, 23-24
             4.4 Unstable Nuclei and Radioactive Decay
Radioactivity = a substance that spontaneously emits radiation.
Radiation = rays and particles (energy) emitted by the radioactive
Nuclear Reaction = A reaction that involves a change in atom’s
nucleus. Unstable atoms breakdown into more stable atoms and
give off radiation in the process.
Radioactive Decay = a spontaneous process that occurs when an
unstable nuclei lose energy by emitting radiation.
Nuclear equation = shows atomic number and mass number of the
particles involved.
Types of Radiation (from weakest to strongest)
  1) Alpha = α = 42 He
         a. Contains two protons and two neutrons
         b. Has a 2+ charge --- why?
         c. Mass = 4 amu
         d. Blocked by a piece of paper
  2) Beta = β = 0-1e
         a. Contains an electron
         b. Has a 1- charge – why?
         c. 1/1840 amu
         d. Blocked by a piece of metal foil
  3) Gamma = γ
          a. High energy electromagnetic radiation
          b. No charge, No mass
          c. Usually accompany alpha or beta radiation
          d. Not completely blocked by lead or concrete
Nuclear Stability
The #1 factor to determine the stability of an atom is its ratio of
neutrons to protons. If there too many or too few the atom is
unstable and will undergo radioactive decay until it becomes
Examples: Assessment pg 124 # 25-29
                          Preview Chapter 24
To break apart
Heavy atom plus a neutron makes the atom unstable and the atom
breaks down into smaller atoms.
One product will be a neutron
The remaining neutrons will cause a chain reaction of splitting
atoms if not stopped.
Example: atomic bomb, nuclear power plant
U-235 + 1 neutron yields Ba-142, Kr-91, 3 neutrons
To put together
Small atoms combine to make a larger atom
One product will be a neutron
Example: hydrogen bomb, sun turns hydrogen into helium giving
off energy
H-3 + H-2 yields He-4 and 1 neutron
Examples: Practice Problems pg 869 #6-8/ Assessment pg 884 #