The Periodic Table
CHAPTER 5
Organizing the Elements
5.1
Organizing Elements Game
 How did you arrange the table?
 Based on your arrangement, where would you put a
card for an element that is a liquid with an atomic
mass between 9 and 13? What would its atomic mass
actually be?
Historic Overview Article
 Trace the evolution of the current Periodic Table by
creating a detailed timeline.

Show important steps in the history of arranging elements in
meaningful ways. Include every step that is listed in the
article!
 Describe the basic tenets of each model for arranging
elements
Questions
 What is the periodic law?
 What is an outlier?
 What element did Mendeleev start his “game of
cards” with? Why did he pick this element (in other
words, why not hydrogen or helium?)
 Why did Mendeleev leave spaces on his version of
the periodic table?
More Questions
 What does interpolated mean?
 What element is named after Mendeleev? What is its
atomic number? How many protons does it have?
Dmitri Mendeleev
 http://www.youtube.com/watch?v=kuQ0Um4Wcz0
Search for Order
 Brings order to seemingly unrelated facts
 Helped chemists predict the existence of elements
that weren’t discovered yet
 Groups elements according to their chemical and
physical properties
Dmitri Mendeleev
 Thought of a way to approach the problem of
organizing the elements while playing solitaire
 Mendeleev made playing cards of the elements that
included the mass and properties of the elements,
then arranged them in order of increasing mass
Mendeleev’s Periodic Table
Strategy for
organization: What
did he look at?
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chemical properties
physical properties
atomic mass
density
color
melting point
Valence electrons
Mendeleev’s Proposal
 Elements arranged in rows based on increasing
mass.
 Elements with similar properties are in same
column.
 Chart was a Periodic Table

arrangement of elements in columns based on a set of
properties that repeat.
Mendeleev’s Prediction
 Table incomplete–
elements not yet
discovered
 Left spaces in table for
undiscovered elements
Evidence Supporting Mendeleev’s Table
 Close match between Mendeleev’s
predictions and the actual
properties of new elements showed
how useful table was.

Ex. Discovery of: Aluminum, Gallium, Scandium, and
Germanium
The Modern Periodic Table
5.2
The Periodic Law
 Elements are arranged by increasing atomic number
 Periods

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Rows of the periodic table
The period number tells us how many energy levels an atom of a
particular element will have
 Groups (or Families)
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Columns of the periodic table
Properties of elements repeat in a predictable way when atomic
numbers are used to arrange elements into groups
Elements in vertical groups have similar electron configurations,
which determines the chemical properties of an element
Periodic Law
The pattern of repeating
chemical and physical
properties that exists in
groups of the periodic table
Atomic Weight (or Atomic Mass)
 A value that depends on the distribution of an
element’s isotopes in nature and the masses of
those isotopes.
Calculating Atomic Weight
 In nature, most elements exist as a mixture of two
or more isotopes.
 Example: There are two natural isotopes of
Chlorine that
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Chlorine – 35
Chlorine – 37

How are these different?
Weighted Averages
 Some isotopes occur more frequently in nature than
do other isotopes
Distribution of Chlorine Atoms in
Nature
Isotope
Percentage
Atomic Mass
Chlorine-35
75.78%
34.969
Chlorine – 37
24.22%
36.966
Classifying Elements
 Can be classified in three ways:
 By state of mater at room temperature (solid, liquid or gas)
 By those that occur naturally and those that do not
 Based on their general properties we can divide them into
METALS, NONMETALS & METALLOIDS
 Periodic Table Coloring Activity
 With a marker, draw solid lines around the following elements

B, Si, Ge, As, Sb, Te, Po, At
Trends in the PT
 Across a period from left to right, the elements
become less metallic and more non-metallic in their
properties
 The most reactive metals are on the left side of the
PT
 The most reactive non-metals are in Group 17
 Complete Side 1 of Element Classification Graphic Organizer
Valence Electrons
 An electron that is in the highest occupied energy level
of an atom
 Elements in a group have similar properties because
they have the same number of valence electrons
 We can illustrate valence electrons using electron dot
diagrams
 Valence electrons are the electrons that participate in
bonding between atoms
Electron Dot Diagram
How do we find the number of valence electrons?
 Look at the Group number!
 The group number tells you how many electrons are in the
outer shell of an atom
 Group 1 – 1 valence electron
 Group 2 – 2 valence electrons
 Group 13 – 3 valence electrons
 Group 14 – 4 valence electrons
 Group 15 – 5 valence electrons
Making Dot Diagrams
 Write down the chemical symbol of the element
 Determine the number of valence electrons
 Use a dot to represent each valence electron by
drawing dots around the chemical symbol

Pretend there is a box around the chemical symbol, putting
single electrons on the edges of the box. After you have put a
single dot on each edge, then start paring up dots with any
remaining electrons.
Example - Carbon
C
Valence Electron Practice
Dot Diagram Game
 4 Teams
 Racing to make correct dot diagrams
 Winning Team gets a HW pass for ONE HW
assignment
 Everyone on your team MUST participate