Mark S. Cracolice
Edward I. Peters
www.cengage.com/chemistry/cracolice
Chapter 5
Atomic Theory:
The Nuclear Model of the Atom
Mark S. Cracolice • The University of Montana
5.1 Dalton’s Atomic Theory
Dalton’s Atomic Theory (1808)
1. Each element is made up of tiny, individual particles called
2.
3.
4.
5.
atoms.
Atoms are indivisible; they cannot be created or destroyed.
All atoms of each element are identical in every respect.
Atoms of one element are different from atoms of any other
element.
Atoms of one element may combine with atoms of other
elements, usually in the ratio of small whole numbers, to form
chemical compounds.
5.1 Dalton’s Atomic Theory
The atoms are neither created nor destroyed in
chemical reactions, but simply arranged
differently to form the products.
5.1 Dalton’s Atomic Theory
Law of Multiple Proportions
When two elements
combine to form more
than one compound, the
different masses of one
element that combine
with the same mass of
the other element are in
a simple ratio of whole
numbers.
Subatomic Particles
Goal 3
Identify the three major subatomic particles by symbol,
charge, and approximate atomic mass, expressed in
atomic mass units.
5.2 Subatomic Particles
Electron
Symbol:
Fundamental charge:
Mass (g):
Mass (atomic mass unit):
Location:
Discovered:
e or e–
1–
9 × 10–28 g
0.000549 u
Outside nucleus
1897 by Thomson
Subatomic Particles
Proton
Symbol:
Fundamental charge:
Mass (g):
Mass (u):
Location:
Discovered:
p or p+
1+
1.673  10–24 g
1.00728 u
Inside nucleus
1919 by Rutherford
Subatomic Particles
Neutron
Symbol:
Fundamental charge:
Mass (g):
Mass (u):
Location:
Discovered:
n or n0
0
1.675  10–24 g
1.00867 u
Inside nucleus
1932 by Chadwick
5.3 The Nuclear Atom
5.3 The Nuclear Atom
The Nuclear Model of the Atom
• An electron with a mass of 1/1837 u could not have
deflected an alpha particle with a mass of 4 u.
• Rutherford concluded that each gold atom contained
a positively charged mass that occupied a tiny
volume. He called this mass the nucleus.
5.3 The Nuclear Atom
The Nuclear Model of the Atom
1. Every atom contains an extremely small, extremely dense
nucleus.
2. All of the positive charge and nearly all of the mass of an
atom are concentrated in the nucleus.
3. The nucleus is surrounded by a much larger volume of nearly
empty space that makes up the rest of the atom.
4. The space outside the nucleus is very thinly populated by
electrons, the total charge of which exactly balances the
positive charge of the nucleus.
5.3 The Nuclear Atom
TThe diameter of an atom
is approximately 10,000
times the diameter of its
nucleus.
5.3 The Nuclear Atom
Planetary Model of the Atom (1911)
Electrons travel in circular orbits around the nucleus,
much like planets move in orbits around the sun.
5.4 Isotopes
Every atom of any particular element
has the same number of protons, which is
called the atomic number, Z.
Atoms are electrically neutral, the number of
electrons in an atom therefore must be equal
to the number of protons.
5.4 Isotopes
All atoms of any particular element are not
identical; the number of neutrons may be
different.
Atoms of the same element that have different
numbers of neutrons—different masses—are
called isotopes.
5.4 Isotopes
An isotope is identified by its mass number, A:
Mass number = A =
Total number of protons + neutrons
Mass number = # of protons + # of neutrons
A
=
Z
+
N
5.4 Isotopes
Name of an Isotope
Elemental name–Mass number
Examples:
What is the name of the carbon atom with 6 protons and 6
neutrons?
Mass number = 6 + 6 =12, so the name is carbon-12
What is the name of the carbon isotope with 7 neutrons?
Mass number is 6 + 7 = 13, so the name is carbon-13
5.4 Isotopes
Symbol of an Isotope
Known as a nuclear symbol
# of protons + # of neutronsSy
# of protons
mass numberSy
atomic number
ASy
Z
Example:
What are the nuclear symbols for carbon-12 and carbon-13?
12C
13C
6
6
5.5 Atomic Mass
Masses of atoms are expressed in
atomic mass units, u.
The u is defined as
1 u  1/12 the mass of one carbon-12 atom
1 u  mass of 1 nuclear subatomic particle
5.5 Atomic Mass
Percentage Abundance of Some Natural Isotopes
Symbol
1H
2H
Mass (u)
1.0078250321
2.0141017780
Percent
99.9885
0.0115
12C
12 (exactly)
13.0033548378
98.93
1.07
38.9637069
39.96399867
40.96182597
93.2581
0.0117
6.7302
13C
39K
40K
41K
5.5 Atomic Mass
This is the mass spectrum of neon.
The relative abundance plotted on
the y-axis is the percentage of
each isotope found in a natural
sample of the pure element.
The mass-to-charge ratio, m/z, is
plotted on the x-axis. Since this
plot shows 1+ ions only, m/z is the
mass of the isotope, expressed in
u.
5.5 Atomic Mass
Atomic mass (of an element):
The average mass of all atoms of an
element as they occur in nature.
Example:
Chlorine has two natural isotopes: 75.78% is chlorine-35 at
34.968852721 u and 24.22% is chlorine-37 at 36.96590262 u.
What is the atomic mass of chlorine?
Solution:
0.7578 × 34.968852721 u = 26.50 u
0.2422 × 36.96590262 u = 8.95 3 u
35.45 u
5.6 The Periodic Table
Periodic Table of the Elements
A table that arranges the elements in order
of increasing atomic number.
Elements with similar properties appear in the
same column.
5.6 The Periodic Table
The Periodic Table
Sample box from the periodic table,
representing sodium.
5.6 The Periodic Table
Periods
Horizontal rows in the periodic table.
Numbered 1–7, top to bottom
(numbers usually not printed).
Groups (or Chemical Families)
Vertical columns in the periodic table.
U.S. numbering: A groups and B groups
IUPAC numbering: 1–18, left to right
5.6 The Periodic Table
Main group elements
(sometimes called representative elements)
Elements in the U.S. A-groups
Transition elements
Elements in the U.S. B-groups
Metals
Elements on the left of the stair-step line
Nonmetals
Elements on the right of the stair-step line
5.7 Elemental Symbols
5.8 Elemental Symbols
Memorize the 35 name–symbol pairs given in Fig. 5.8.
Look at the location of each element in the periodic table while
you work on memorization—it will help you remember the
names and symbols.
Whenever a chemical symbol has two letters,
the first letter is always capitalized and
the second letter is always written in lowercase.
Homework
Homework for chapter 5:
17, 19, 21, 27,29, 31, 39, 41, 54