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THE ATOM
Smallest part of an element that
has all of the properties of that
element.
HISTORY
 Greeks and matter
 John Dalton’s atom
 Dmitri Mendeleev
 Earth, wind, water, air and fire
 Matter classified by atomic mass
 Hook and eye
 Elements composed of identical atoms
reacted in the same way
 Arranged atoms in order of increasing
mass.
 Designed 1st periodic table
 (modern table arranges elements that
react the same chemically)
History cont.
 Thomson’s atom
 Plum pudding
 Electrons are negative (plums)
 Pudding is positive
 Ernest Rutherford
 Placed the nucleus in the center
 Nucleus had a positive charge
 Neils Bohr
 Atom is a mini solar system
Questions for you
What do particle accelerators do?
AMU is the acronym for
Smallest part of an element is a
Smallest part of a compound is a
Fundamental parts of the atom are
Atomic mass number for an electron is
What are the two types of nucleons
Which of the fundamental particles is
heaviest?
Which has a positive charge?
Which is electrically neutral?
Nucleons are ______times the mass of an
electron
Which particle ultimately determines the
chemical behavior of an atom?
A neutral atom has the _____number of
electrons in orbits as protons in the
nucleus
K LMNOP Q
Electron Arrangement
Review of the Periodic Table
The outermost shell is identified by the period
and the number of electrons in the outermost
shell is identified by the group
Shell number –n- AKA Principle Quantum
Number 2n
Atoms with filled outer shells are stable
Number of electrons in outer shell determines
the chemical reaction
2
Transitional Elements
Fourth period
Electrons are added to inner shells
Chemical properties of transitional
elements are dependent on number of
electrons in the TWO OUTERMOST
SHELLS
CENTI
FUGAL FORCE
FLYING OUT INTO
SPACE
CENTRI
PETAL FORCE
PULLING INTO THE
CENTER
Electrostatic attraction
Opposites charges attract
Eb
The closer the electron is to the nucleus,
the stronger the Eb.
Eb
The greater the number of electrons, the
more tightly they are bound
THEREFORE
The larger the atom, the higher
the electron binding energy
We can now deduce
More electrons mean higher atomic
number because
The number of electrons = the number of
protons and atomic number is determined
by the number of protons
In Radiography
Tungsten is used to construct the anode
and cathode because it has a high atomic
number
A high atomic number means more energy
is required to ionize the material
Recall that ionization causes eventual
breakdown of material
Radioactivity
What determines if a nucleus of an atom is
unstable?
Too many or too few neutrons
Radioactivity
Nucleus is unstable
In an attempt to become stable, emits
particles and energy
This is called radioactive decay or
disintegration
Atoms are called radionuclide
 Alpha
 Beta
 Loses 2 units of
positive charge
 Loses 4 units of mass
 Emits gamma rays
 High QF
 High LET
 Neutrons converts to
a proton
 Electron type of
particle is ejected
 Increases the atomic
number by one
 Emits gamma rays
IONIZATING RADIATION AGAIN!!!!!
 Alpha
 Emitted only from nuclei
of heavy elements
(helium)
 Travel quickly thru matter
 Ionization is quick
 Harmless if deposited
outside of body
 Inside it can completely
irradiate soft tissue
 Beta
 Longer range than Alpha
 Originate from the nuclei
of radioactive atoms.
 See figure 4-18, pg 56
Radioactive half life
Time needed for a radioisotope to
disintegrate into a stable atom
Period of time for the radioactivity to be
reduced to half its original value
Never reaches zero