Chapter 5 Atomic Theory: The Nuclear Model of the Atom. 5.1 Dalton ’ s Atomic Theory. Dalton ’ s Atomic Theory (1808) Each element is made up of tiny, individual particles called atoms. Atoms are indivisible; they cannot be created or destroyed.
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Chapter 5Atomic Theory:The Nuclear Model of the Atom
Dalton’s Atomic Theory (1808)
The atoms are neither created nor destroyed in chemical reactions, but simply arranged differently to form the products.
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.
Identify the three major subatomic particles by symbol, charge, and approximate atomic mass, expressed in atomic mass units.
Symbol:e or e–
Mass (g):9 × 10–28 g
Mass (atomic mass unit):0.000549 u
Discovered:1897 by Thomson
Symbol:p or p+
Mass (g):1.673 10–24 g
Mass (u):1.00728 u
Discovered:1919 by Rutherford
Symbol:n or n0
Mass (g):1.675 10–24 g
Mass (u):1.00867 u
Discovered:1932 by Chadwick
The Nuclear Model of the Atom
The Nuclear Model of the Atom
TThediameter of an atom is approximately 10,000 times the diameter of its nucleus.
Planetary Model of the Atom (1911)
Electrons travel in circular orbits around the nucleus,
much like planets move in orbits around the sun.
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.
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.
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
Name of an Isotope
Elemental name–Mass number
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
Symbol of an Isotope
Known as a nuclear symbol
What are the nuclear symbols for carbon-12 and carbon-13?
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
Percentage Abundance of Some Natural Isotopes
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.
Atomic mass (of an element):
The average mass of all atoms of an
element as they occur in nature.
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?
0.7578 ×34.968852721 u = 26.50 u
0.2422 ×36.96590262 u = 8.95 3 u
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.
Sample box from the periodic table, representing sodium.
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
Main group elements
(sometimes called representative elements)
Elements in the U.S. A-groups
Elements in the U.S. B-groups
Elements on the left of the stair-step line
Elements on the right of the stair-step line
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 for chapter 5:
17, 19, 21, 27,29, 31, 39, 41, 54