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ATOMIC
STRUCTURE
Dalton’s Theory
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All matter is made up of tiny particles called
atoms
Atoms of the same element are identical in
size, mass, properties
Atoms cannot be subdivided, created or
destroyed
Atoms of different elements combine to form
chemical compounds
How much of this is true?
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Some of Dalton’s Theory about the atom has
been altered based on new information
This gives us the …..
Modern Atomic Theory
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All matter is made up of atoms.
Atoms of the same element are chemically
similar
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Atoms of an element may not have the same
mass (Isotopes)
Atoms are not subdivided, created or
destroyed in chemical reactions.
Isotopes
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Atoms of the same element with different
masses
Protons are the same
Neutrons differ
235
Looks like: uranium-235
Or
92
U
Ions
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Have an unequal number of protons and
electrons
Have an overall positive or negative
charge
Atomic Number
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It represents the # of protons
It can also represent the # of electrons if the
atom is neutral
Mass Number
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Represents the # of protons + # of neutrons
# of Neutrons = Mass Number – Atomic Number
Subatomic Particles
Particle
Location
Charge
Mass
Periodic Table
13
Al
26.98154
Periodic Table
19
K
39.0983
Nuclear Symbols
27
13
Al
57
26
Fe
Nuclear Symbols
27
13
Al
3+
35
17
Cl
1-
Elements, Isotopes
and Ions
127
I
127 -
I
129
I
Describing the Atom
J.J. THOMPSON - Showed that
atoms are made of particles
CATHODE
RAY
TUBE
\
Describing the Atom
MILLIKAN
Calculated the charge on a
single electron
Rutherford
Showed that atom had both + and charges : Radiation and Magnets (p106)
Rutherford
Showed atom mostly empty space & its
mass is contained in a very small area
GOLD FOIL
EXPERIMENT
See p 95
C:\Documents and Settings\Teacher\Desktop\1Rutherford_Expt.avi
Gold Foil Experiment
Flame Test
*Electrons
exist in energy levels (or
‘shells’).
*When exposed to an energy source,
electrons may become ‘excited’ and
jump to a higher energy level.
*When the electron returns to its
‘ground state’ a photon of light is
released.
*The photon of light is always the same
wavelength (and the same color) for
each element.