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Transcript
The
Structure of
the Atom
Important contributors to the Atomic
Theory

Democritus
Dalton
Rutherford

Aristotle
J. J. Thomson
Bohr
The Atom: Early Theories

Democritus versus Dalton similarities
– Both believed
 Matter composed of extremely small particles
called atoms
 All atoms of a given element are identical, but
different from the atoms of other elements
 Atoms could not be created, divided, or destroyed
 Apparent changes in matter result from changes in
the groupings of atoms
The Atomic Theory: Democritus and
Dalton differences
– Democritus
Matter is composed of empty space through
which atoms move
 Different kinds of atoms come in different
sizes and shapes
 The differing properties of atoms are due to
the size, shape, and movement of atoms
– Dalton
 Different atoms combine in simple whole
number ratios to form compounds

Dalton’s Atomic Theory
The Atom: Subatomic particles and the
nuclear atom

How were the various parts of the atom
discovered?
– Electrons were discovered by the experiments
of many scientists using cathode rays.
 JJ Thomson was able to determine the ratio
of the electron’s charge to its mass
 Robert Millikan determined the charge of
the electron and was able to calculate the
mass of a single electron
http://www.learnerstv.com/animation/animation.php?ani=18
6&cat=chemistry
J. J. Thomson: Plum Pudding Model
Discovery of subatomic particles
– The nucleus was discovered by Ernest Rutherford
and his gold foil experiment
http://www.youtube.com/watch?v=5pZj0u_XMbc
Rutherford refined his definition to include the
proton
 Rutherford and James Chadwick discovered the
neutron

The atom

Bohr- e- only have “allowable E states”

e- around nucleus in orbits
Particle
Symbol Location
electron e-
Relative Relative Actual mass
charge
mass
(g)
electron cloud
1-
1/1840
9.11 x 10-28
proton
p+
nucleus
1+
1
1.673 x 10-24
neutron
n0
nucleus
0
1
1.675 x 10-24
The Atom: How Atoms Differ
Chemical name
Atomic number
Chemical Symbol
Average Atomic Mass
Atomic number = number of protons = number of electrons
How many protons and electrons are in each of the following
atoms?
– boron
– radon
– platinum
– magnesium
An atom of an element contains 66 electrons. What element is
it?
An atom contains 14 protons. What element is it?
Hydrogen
1
H
1.00794




LET’S REVIEW…
1.
2.
3.
4.
5.
Which scientist came up with the plum pudding
model?
Why was it called this?
Who discovered the nucleus of the atom?
What was wrong with Dalton’s atomic theory?
How many protons, neutrons, and electrons are
in each of the following atoms?
a) boron
b) radon
Let’s Review: Answers
1.
2.
3.
4.
5.
Which scientist came up with the plum pudding
model? J. J. Thomson
Why was it called this?
Who discovered the nucleus of the atom?
Rutherford
What was wrong with Dalton’s atomic theory?
He stated that the atom was “indivisible”
How many protons, neutrons, and electrons are in each
of the following atoms?
a) Boron: p+, e- = 5, no= 6
b) Radon: p+, e- = 86, no= 136
The Atom: How Atoms Differ cont

Isotopes
– An element with a different amount of neutrons in its nucleus
– PROTON determines the ID
– Representing isotopes:
How atoms differ
– Element – mass #
– carbon – 12, carbon – 13, carbon – 14
– The mass number represents the total protons and neutrons in
an element
– How many protons, electrons, and neutrons in the following
isotopes? Name each isotope and write its symbol.
Atomic Structure: Isotopes

Atomic masses of elements on the table are based on
naturally occurring isotopes
 Weighted scale – abundance(mass)
Average atomic mass =
(mass 1 x rel. abundance 1) + (mass 2 x rel. abundance 2)
 Element C has two naturally occurring isotopes. The
isotope with mass number 10 has a relative abundance of
20%. The isotope with mass number 11 has a relative
abundance of 80%.
 Use these figures to estimate the average atomic mass for
element C. State the atomic number and the true value of
element C
Atomic Structure: Isotopes
– Complete the following table
Isotope
Atomic # Mass #
20
46
8
17
p+
e-
n0
symbol
107
Ag
47
hydrogen-3

Types of Radiation
– Alpha Radiation: radiation that is deflected
toward the negatively charged plate. Each
alpha particle contains two protons and two
226
222
4
neutrons.
Ra

Rn

88
86
2 He
– Beta Radiation: radiation that was deflected
toward the positively charged plate. Each
beta particle is an electron.
14
6
C N  
238
92
4
0
Ra234
Th

He

2
90
2
0
14
7
o
1
– Gamma Radiation: high energy radiation that
possesses no mass
The Atom Review

Atomic theories
– Democritus vs. Dalton
 Subatomic particles and the atom
– JJ Thompson – determined the charge to mass ratio of the
electron
– Robert Millikan – determined the charge and mass of the
electron
– Rutherford – discovered the nucleus and later the proton
– Rutherford and James Chadwick – discovered the neutron
 Atomic Number
 Isotopes
 Average Atomic Mass
 Types of Radiation