Download Atomic Structure

MATTER UNIT
STRUCTURE OF AN ATOM
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WHAT IS AN ATOM?
Atom: the
smallest unit of
matter that retains the identity
of the substance
THE EVOLUTION OF ATOMIC STRUCTURE
460 B.C. – DEMOCRITUS
• DEMOCRITUS BELIEVED
THAT ALL MATTER WAS
COMPOSED OF ATOMS
THAT COULD BE DIVIDED
NO FURTHER.
1800 – JOHN DALTON
DALTON'S ATOMIC THEORY:
MATTER IS COMPOSED OF SMALL PARTICLES CALLED ATOMS.
ALL ATOMS OF AN ELEMENT ARE IDENTICAL, BUT ARE
DIFFERENT FROM THOSE OF ANY OTHER ELEMENT.
DURING CHEMICAL REACTIONS, ATOMS ARE NEITHER CREATED
NOR DESTROYED, BUT ARE SIMPLY REARRANGED.
ATOMS ALWAYS COMBINE IN WHOLE NUMBER MULTIPLES OF
EACH OTHER. FOR EXAMPLE, 1:1, 1:2, 2:3 OR 1:3.
1897- J.J. THOMSON
THOMSON’S RAISIN IN THE PUDDING MODEL OF
THE ATOM
• HE DISCOVERED THE ELECTRON AND PROPOSED A MODEL
FOR THE STRUCTURE OF THE ATOM.
Positive Sphere
Negative
Charges
Discovery of the Electron
1910 – ERNST RUTHERFORD
Rutherford’s Gold Foil Experiment
Rutherford’s Findings
“Like howitzer shells bouncing
off of tissue paper!”
Conclusions:
 The nucleus is small
 The nucleus is dense
 The nucleus is positively
charged
1912 – NIELS BOHR
Bohr’s Finding:
 Quantized energy levels
 Electron moves in a circular orbit
 Electron jumps between levels by
absorbing or emitting photon of a
particular wavelength
HOW EXACTLY ARE THE
PARTICLES ARRANGED?

Bohr Model of the atom:
All of the
protons and the
neutrons
The 3rd ring can
hold up to 8 eThe 4th ring and any
after can hold up to
18 e-
The 1st ring can
hold up to 2 eThe 2nd ring can
hold up to 8 e-
WHAT DOES CARBON LOOK LIKE?
Mass # = 12
atomic # = 6
6 p and 6 n live
in the nucleus
p+ = 6
no = 6
e- = 6
JAMES CHADWICK
1932
Discovered the
Neutron.
QUANTUM MECHANICAL MODEL
• ELECTRONS ARE LOCATED IN SPECIFIC
ENERGY LEVELS.
• THERE IS NO EXACT PATH AROUND
THE NUCLEUS.
• THE MODEL ESTIMATES THE
PROBABILITY OF AN ELECTRONS
POSITION
THE ELECTRON CLOUD
THE ELECTRON CLOUD
CONTAINS THE ELECTRONS.
MODERN ATOMIC THEORY
• ELEMENT HAVE A CHARACTERISTIC AVERAGE MASS
WHICH IS UNIQUE TO THAT ELEMENT.
• ATOMS CANNOT BE SUBDIVIDED, CREATED, OR
DESTROYED IN ORDINARY CHEMICAL REACTIONS.
HOWEVER, THESE CHANGES CAN OCCUR IN
NUCLEAR REACTIONS!
• ALL MATTER IS COMPOSED OF ATOMS
• ATOMS OF ANY ONE ELEMENT DIFFER IN PROPERTIES
FROM ATOMS OF ANOTHER ELEMENT
 Atoms
ATOMIC STRUCTURE
are composed of 2 regions:
Nucleus: the center of the atom that contains the
mass of the atom
Electron cloud: region that surrounds the nucleus
that contains most of the space in the atom
Electron
Cloud
Nucleus
ATOMIC STRUCTURE
The nucleus contains 2 of the 3
subatomic particles:
Protons: positively charged
subatomic particles
Neutrons: neutrally charged
subatomic particles
The 3rd subatomic particle resides
outside of the nucleus in the
electron cloud
Electron: the subatomic particle
with a negative charge and
relatively no mass
Atomic Particles
Particle
Charge
Electron
-1
Mass
#
0
Proton
+1
0
Neutron
Location
symbol
Electron
cloud
e-
1
Nucleus
p+
1
Nucleus
n0
HOW DO THESE
PARTICLES INTERACT?
Protons
and neutrons are in the tiny
positively charged nucleus accounting for
most of the mass of the atom
The negatively charged electrons are
small and have a relatively small mass but
occupy the larger volume of space outside
the nucleus
HOW DO THE SUBATOMIC PARTICLES
BALANCE EACH OTHER?
In
an atom:
 The
# of protons = The # of electrons
If
20 protons are present in an atom then 20
electrons are there to balance the overall charge
of the atom—atoms are neutral
The
neutrons have no charge
they
do not have to equal the number of
protons or electrons
THE NUMBER OF
PROTONS IDENTIFIES
THE ATOM.
• AN ATOM WITH 6 PROTONS = CARBON
• AN ATOM WITH 8 PROTONS = OXYGEN
• AN ATOM WITH 20 PROTONS = CALCIUM
ATOMIC STRUCTURE
He
2 Atomic number
the number of protons
in an atom
4 Atomic mass
the number of protons and
neutrons in an atom
# of electrons = # of protons
# of neutrons = Atomic mass – # of protons
DETERMINE THE NUMBER OF SUBATOMIC
PARTICLES IN THE FOLLOWING:

Cl has a mass # of 35 and an atomic #
of 17
 p+

= 17,
no = 18,
e- = 17
K has a mass # of 39 and an atomic #
of 19
 P+
= 19,
no = 20
e- = 19