Download Atoms - Dr. Vickie M. Williamson

Dr. Williamson’s Atoms ppt
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Atoms
Dr. V.M. Williamson
Democritus
! 
Greek philosopher
Democritus began the
search for a description of
matter more than ______
years ago.
"  He asked: Could matter be divided
into smaller and smaller
pieces forever, or was there a limit to the
number of times a piece
of matter could be
divided?
Atomos
400 BC
!  His
theory: Matter could
not be divided into smaller
and smaller pieces forever,
eventually the smallest
possible piece would be
obtained.
!  This piece would be
_________________.
!  He named the smallest
piece of matter “atomos,”
meaning “not to be cut.”
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Dr. Williamson’s Atoms ppt
Atomos
# 
To Democritus,
atoms were small,
hard particles that
were all made of the
same material but
were different
shapes and sizes.
# 
Atoms were
_______ in number,
always moving and
capable of joining
together.
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This theory was ignored
and forgotten for more
than ______ years!
Leucippus from the same
time also given credit for
the belief in atoms
! 
Why forgotten?? The
eminent philosophers
of the time, Aristotle
and Plato, had a more
respected, (and
ultimately wrong)
theory.
Aristotle rejected atoms. He and Plato
favored the belief in 4 types of matter: earth,
fire, air and water. Their ideas held sway
because of their eminence as philosophers.
The atomos idea was buried for approximately ____ yrs.
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Dr. Williamson’s Atoms ppt
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John Dalton
!  English
chemist,
a quaker,
employed as a
teacher,
discovered he
was color blind
to red at 26, shy,
suffered from
lead poisoning
from drinking
stout.
(1766-1844)
John Dalton
■  Dalton’s
work
eventually led to
the acceptance of
the idea of atoms
and changed the
way symbols were
used. Symbols
now for elements,
not words
Father of Modern
Chemical Theory
quote
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Dr. Williamson’s Atoms ppt
© vm williamson
Dalton’s Theory-1803
All matter composed of atoms. Atoms are
indivisible and indestructible particles.
!  Atoms of the _______ element are exactly
alike and differ from those of other
elements.
!  __________ are formed by the joining of
atoms of two or more elements.
!  A given compound always has the ______
number and type of atoms.
!  Atoms are not created or destroyed, only
______________, in chemical reactions.
! 
Symbols
!  Like
alphabet: alphabet
shorthand for sounds, symbols
shorthand for elements
!  Symbols are:
" First
letter
2 letters (uppercase, then lower)
" First letter(s) of latin, greek, or
german name
" First
Elements
!  118
made or predicted
are natural except Tc (in lab only),
Fr, Pm, &At (very minute, artificial
samples used to get properties) _______
naturally occuring
!  ______ and above are synthetic
!  See objectives about which symbols and
names to know
!  Atoms =
!  Molecule =
!  1-92
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Dr. Williamson’s Atoms ppt
© vm williamson
Some Common Elements
!  Al
!  B
!  Br
!  C
!  Ca
!  Cl
!  H
!  He
!  N
!  O
aluminum
boron
bromine
carbon
calcium
chlorine
hydrogen
helium
nitrogen
oxygen
!  Ag
silver (argentium)
gold (aurum)
!  Cu copper (cuprum)
!  Fe iron (ferrum)
!  Hg mercury (hydragyrum)
!  K potassium (kalium)
!  Na sodium (natrium)
!  Pb lead (plumbum)
!  Sn tin (stannum)
!  W tungsten (wolfram)
!  Au
Periodic Table of the Elements
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Dr. Williamson’s Atoms ppt
! 
Understanding of atoms build slowly
from indirect evidence. Lots of
experiments, theories proposed and
abandoned.
! 
Dalton proposed his Atomic Theory in
1803.
! 
Now: What is the nature of the atom?
Was the atom homogeneous (_____
_________) throughout?
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Objective: Nuclear Evidence
Joseph John Thomson (1856-1940;
Nobel Prize 1906) described cathode
rays. ! 
■  Cathode
rays
are radiation
produced from
high voltage
through partially
evacuated gas
tubes.
■  These
rays traveled in straight lines,
but were attracted to the ________
________ of electricity & magnets,
indicating the rays are ___________.
■  (SEE DEMO & overhead)
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Dr. Williamson’s Atoms ppt
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Copyright © 1995 by Saunders College Publishing
Thomson and the Cathode Ray Tube
! 
Results were the same with tubes
containing 20 different metals as the
electrode or with several different gases.
! 
When a small paddle wheel was placed in
the path of cathode rays, the wheel was
set in motion. The rays were thought to be
composed of _________________ that
were called “corpuscles,” later
ELECTRONS
! 
Conclusion: All metals and gases (and
probably all atoms) contain
_____________.
But, atoms are neutral, so atoms must
contain __________charges to balance
the __________ charges of the
electrons. Thomson was never able to
find the ________ particles.
!  In 1897, Thomson measured the
electrical charge to mass ratio of an
electron.
! 
! 
Which of Dalton’s theories was now
abandoned?____________________
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Dr. Williamson’s Atoms ppt
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Electrons of atom were thought to be
embedded in a positively charged ball
of matter. This is the plum pudding or
________ model. Imagine the purple
ovals to be electrons.
! 
Property of the Electron
Copyright © 1995 by Saunders College Publishing
Millikan’s Oil Drop Experiment
! 
Robert A Milliken (1868-1953; Nobel Prize
1923) did an experiment in 1909 to
determine the charge of an electron, then
calculated the mass.
! 
See overhead.
Mass & Charge of an electron: ____________ g or 5.486 x 10-4AMU and
_______________ Coulombs
!  (No, don’t memorize the mass &charge,
but know that these exist.)
! 
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Dr. Williamson’s Atoms ppt
■ 
A New Zealander, Ernest Rutherford
(1871-1937) and his team made the plum
pudding model obsolete. ■ 
The experiment was to direct a beam of ________________ particles at a thin piece of gold foil. Around the foil was a screen coated with zinc sulfide which gave flashes of light when the particles struck it.
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Structure of the Atom
Rutherford’s Experiment
! 
Then read Rutherford’s words:
“It was quite the most incredible event that
has ever happened to me in my life. It was
almost as if you fired a 15-inch shell into a
piece of tissue paper and it came back and
hit you!!”
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Dr. Williamson’s Atoms ppt
© vm williamson
Structure of the Atom
Rutherford’s Experiment
For _________ particles to be deflected,
there must be a heavy _____ object in the
atoms of gold, with mostly open space.
!  By 1911, we had the NUCLEAR atom or
Rutherford model. The nucleus was
thought to be small, dense (heavy),
________, and surrounded by electrons.
! 
If the nucleus were
the size of a pea,
the atom would
have a mass of 250
million tons!
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Dr. Williamson’s Atoms ppt
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Rutherford Model
Copyright © 1999 by HOLT Publishing
! 
By 1919, protons were thought to be in
nucleus. They had the opposite charge
of an electron, but were much
____________.
! 
By 1932, James Chadwick discovered
that the nucleus also contained
__________ particles. Neutrons had no
charge, but were slightly more massive
than protons.
Objective: Composition
! 
If all atoms are made of protons,
electrons, and neutrons, what makes
them different? (We know different
elements have different properties.)
! 
Atoms of the same element have the
same number of protons. The number
of protons is called the
___________________.
#6 = C #20 = ______ #8 = _____
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Dr. Williamson’s Atoms ppt
! 
What is the number of electrons in an
aluminum atom? ______
! 
The number of protons = the number of
electrons in a neutral atom, this is same
as the ________ _____________. ! 
The nucleus takes up very little space
in the atom. If the nucleus is a grape,
the outer edge of the atom is one mile
away. See overhead.
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COMPARISONS OF ATOMIC PARTICLES
■  Particle____Actual Charge____Relative Charge
Electron -1.602 x 10-19 C
-1
Proton
+1.602 x 10-19 C
+1
Neutron
none
0
■ 
Particle__Actual Mass Relative to E Relative to N
Electron 9.10939 x 10-28g
1
0.0005438
Proton
1.672 x 10 -24g
1836
0.9984
Neutron 1.675 x 10 -24g
1839
1
Objective: e,p,n from Notation
! 
The mass of an atom depends on the protons
and neutrons. Protons + Neutrons = ____________.
! 
Nuclear Symbols:
The generic form is
A
Z
Where A =___________= ____________
and Z = ____________= _____________
X
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Dr. Williamson’s Atoms ppt
© vm williamson
Atomic Notation: Nuclide Symbol
Mass number
Atomic number
●  The
A
X
Element symbol
Z
23
atom with the symbol 11 Na
has:
✻  11
protons
✻  11 electrons
✻  12 neutrons
✻  mass of 23 atomic mass units
!  20Ne
or just
20Ne
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Give the number of:
protons = ____________
electrons = ___________
neutrons = ____________
!  22Ne
or just
22Ne
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protons = ______, neutrons= ______,
electrons =_______
Objective: Isotopes
!  20Ne
or just
20Ne
or Neon-20
10
And
22
Ne or just
22Ne
or Neon-22 10
are isotopes. ! 
Isotopes have the __________atomic
number or # of p, but ________ mass
numbers or # of neutrons.
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Dr. Williamson’s Atoms ppt
© vm williamson
Objective: Atomic Mass
Notice that on the periodic table the masses
of elements are not even numbers. Atomic
mass is the weighted average of the masses
of naturally occurring ___________.
!  There are three isotopes of carbon. The % of
each in nature is:
12C = 98.892% 13C = 1.108% 14C = 2 x 10-10%
!  12C has 6 p + 6 n and has a mass of 12 AMU
!  To find the atomic mass for C on the table:
(______________ x 12) + (________________ x
13) + (________________ x 14)
= 12.011 AMU
! 
Objective: Ions
! 
Ions are produced when an atom loses or
gains electrons.
! 
So an ion with 20 protons, and 18
electrons would be ____________.
! 
An ion of copper-64 has a charge of -1. How many of each particle are
present: p = ________, e = _______, & n =
____________
! 
The Rutherford model of the atom was
abandoned because an observation
was made in the lab that his model
couldn’t explain.
! 
This covers objectives 1-8 on Atoms
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