Download The Periodic Table Section 1 Atomic Masses

The Periodic Table
Section 1
Section 2: A Guided Tour of the Periodic
Table
Preview
• Key Ideas
• Bellringer
• Recognizing a Pattern
• Changing the Arrangement
• The Periodic Table of the Elements
The Periodic Table
Section 1
Key Ideas
〉How did Mendeleev arrange the elements in his
periodic table?
〉How are elements arranged in the modern
periodic table?
The Periodic Table
Section 1
Bellringer
One way to organize a large group of objects is to arrange them into
groups of similar objects. This is how scientists organize all of the many
elements. Practice the skill of categorizing by arranging the magazines
listed below into similar groups.
Calling All Girls
Computer World
Beautiful Homes
Auto Racing
The Healthy Man
Sporting Times
Child’s Play
Family Computing
Beautiful Homes
Car Trends
Homeopathic Medicine
Sports and Scores
Calling All Boys
All About Computing
Home Decorating
Classic Cars
The Healthy Woman
Golf for Everyone
Nursery Rhymes
How to Use the Internet
Modern Housekeeping
Easy Car Repairs
The Health Newsletter
Football Stories
Read Aloud Stories
Building a Web Site
Home Makers Magazine
The Sports Car Story
Good Nutrition
Tennis Tips
The Periodic Table
Section 1
Bellringer, continued
1. Arrange the magazines into similar groups.
2. What criteria did you use for grouping the magazines?
3. Once you arrange the magazines into groups, could you sort the
material further to make it even more organized?
Calling All Girls
Computer World
Beautiful Homes
Auto Racing
The Healthy Man
Sporting Times
Child’s Play
Family Computing
Beautiful Homes
Car Trends
Homeopathic Medicine
Sports and Scores
Calling All Boys
All About Computing
Home Decorating
Classic Cars
The Healthy Woman
Golf for Everyone
Nursery Rhymes
How to Use the Internet
Modern Housekeeping
Easy Car Repairs
The Health Newsletter
Football Stories
Read Aloud Stories
Building a Web Site
Home Makers Magazine
The Sports Car Story
Good Nutrition
Tennis Tips
The Periodic Table
Section 1
Recognizing a Pattern
〉How did Mendeleev arrange the elements in his
periodic table?
〉In his periodic table, Mendeleev arranged
elements in rows by increasing atomic mass.
The Periodic Table
Section 1
Recognizing a Pattern, continued
• Mendeleev was able to predict new elements.
– Mendeleev left spaces in his
table to make the pattern fit.
– He used the spaces to
successfully predict the
existence and properties of
elements not yet discovered.
• A few elements did not fit the pattern.
The Periodic Table
Section 1
Changing the Arrangement
〉How are elements arranged in the modern
periodic table?
〉The modern periodic table organizes elements
by atomic number. When the elements are
arranged in this way, elements that have similar
properties appear at regular intervals.
The Periodic Table
Section 1
Changing the Arrangement, continued
• As scientists learned more about the structure of the
atom, they improved Mendeleev’s table.
• Arranging the table by atomic number (number of
protons) rather than by atomic mass fixed the
discrepancies in Mendeleev’s table.
• periodic law: the law that states that the repeating
chemical and physical properties of elements change
periodically with the atomic numbers of the elements
The Periodic Table
Section 1
The Periodic Table of the Elements
The Periodic Table
Section 1
Changing the Arrangement, continued
• Elements become less metallic across each period.
– period: a horizontal row of elements in the periodic
table
• Elements in a group have similar properties.
– group: a vertical column of elements in the periodic
table; elements in a group share chemical properties
The Periodic Table
Section 1
Visual Concept: Periodic Table Overview
Click the button below to watch the Visual Concept.
The Periodic Table
Section 1
The Role of Electrons
〉Why do elements within a group of the periodic
table have similar chemical properties?
〉The periodic trends in the periodic table are the
result of electron arrangement.
The Periodic Table
Section 1
The Role of Electrons, continued
• Valence electrons account
for similar properties.
• An element’s location in
the periodic table is
related to electron
arrangement.
– Example: Lithium and
sodium, in Group 1, each
have one valence
electron.
The Periodic Table
Section 1
Ion Formation
〉What happens to an atom that gains or loses
electrons?
〉If an atom gains or loses electrons, it no longer
has an equal number of electrons and protons.
Because the charges do not cancel completely,
the atom has a net electric charge.
The Periodic Table
Section 1
Ion Formation, continued
• Group 1 elements
form positive ions.
– The single valence
electron is easily
removed.
• Group 17 elements
form negative ions.
– The addition of one
valence electron fills
the outer energy level.
The Periodic Table
Section 1
Atomic Number and Mass Number
〉What do atoms of an element have in common
with other atoms of the same element?
〉Atoms of each element have the same number
of protons, but they can have different
numbers of neutrons.
The Periodic Table
Section 1
Atomic Number and Mass Number,
continued
• The atomic number equals the number of protons.
– atomic number: the number of protons in the
nucleus of an atom
• The mass number equals the total number of
subatomic particles in the nucleus.
– mass number: the sum of the numbers of protons
and neutrons in the nucleus of an atom
The Periodic Table
Section 1
Atomic Number and Mass Number,
continued
The Periodic Table
Section 1
Isotopes
〉Why do isotopes of the same element have
different atomic masses?
〉Isotopes of an element vary in mass because
their numbers of neutrons differ.
The Periodic Table
Isotopes, continued
Section 1
The Periodic Table
Section 1
Isotopes, continued
• The number of neutrons can be calculated.
– number of neutrons = mass number – atomic number
The Periodic Table
Section 1
Atomic Masses
〉What unit is used to express atomic mass?
〉Because working with such tiny masses is
difficult, atomic masses are usually expressed
in unified atomic mass units.
• unified atomic mass unit: a unit of mass that
describes the mass of an atom or molecule; it is
exactly 1/12 the mass of a carbon atom with mass
number 12 (symbol, u)
The Periodic Table
Section 1
Atomic Masses, continued
• Average atomic mass is a weighted average.
– Isotope abundance
determines the average
atomic mass.
– Example: Chlorine-35 is
more abundant than
chlorine-37, so chlorine’s
average atomic mass
(35.453 u) is closer to 35
than to 37.