Download Atoms - Dr. Vickie M. Williamson

Dr. Williamson’s Atoms ppt
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Democritus
! 
Atoms
Dr. V.M. Williamson
Atomos
!  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.”
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
! 
This theory was ignored
and forgotten for more
than ______ years!
Leucippus from the same
time also given credit for
the belief in atoms
400 BC
# 
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.
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
© vm williamson
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 Theory-1803
■  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
Symbols
!  Like
alphabet: alphabet
shorthand for sounds, symbols
shorthand for elements
!  Symbols are:
" First
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.
! 
letter
" First 2 letters (uppercase, then lower)
" First letter(s) of latin, greek, or
german name
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
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)
!  Au 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)
Objective: Nuclear Evidence
Joseph John Thomson (1856-1940;
Nobel Prize 1906) described cathode
rays. ! 
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Periodic Table of the Elements
! 
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?
■  These
rays traveled in straight lines,
but were attracted to the ________
________ of electricity & magnets,
indicating the rays are ___________.
■  (SEE DEMO & overhead)
■  Cathode
rays
are radiation
produced from
high voltage
through partially
evacuated gas
tubes.
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Dr. Williamson’s Atoms ppt
© vm williamson
! 
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
_____________.
! 
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.
Copyright © 1995 by Saunders College Publishing
Thomson and the Cathode Ray Tube
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?____________________
Property of the Electron
! 
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.)
! 
Copyright © 1995 by Saunders College Publishing
Millikan’s Oil Drop Experiment
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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
Structure of the Atom
! 
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!!”
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
© vm williamson
! 
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.
! 
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.
Rutherford Model
Copyright © 1999 by HOLT Publishing
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 = _____
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
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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 = ____________= _____________
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X
Dr. Williamson’s Atoms ppt
© vm williamson
!  20Ne
Atomic Notation: Nuclide Symbol
Mass number
Atomic number
●  The
A
X
Z
!  22Ne
or just
20Ne
Ne or just
or Neon-20
22Ne
22Ne
protons = ______, neutrons= ______,
electrons =_______
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
! 
10
22
or just
10
Objective: Atomic Mass
Objective: Isotopes
or Neon-22 10
are isotopes. ! 
23
atom with the symbol 11 Na
has:
protons
✻  11 electrons
✻  12 neutrons
✻  mass of 23 atomic mass units
And
20Ne
Give the number of:
protons = ____________
electrons = ___________
neutrons = ____________
Element symbol
✻  11
!  20Ne
or just
10
Isotopes have the __________atomic
number or # of p, but ________ mass
numbers or # of neutrons.
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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