Chapter 3: Introduction to the Periodic Table

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Chapter 3 Introduction to the Periodic Table

• Section 3.1 Development of the Periodic Table

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• Objectives Summarize the steps in the
  historical development of the periodic table,
  Predict similarities in properties of the
  elements by using the periodic table

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Organization

• Scientists noticed that some elements had similar
  properties and they wanted to organize the
  elements into a system that would show
  similarities and acknowledge difference
• http//www.ptable.com/

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J.W. Dobereiners Triads (1829)

• Classified some elements in groups of three-
  called triads
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• Triads had similar properties and varied in an
  orderly way according to their atomic masses
• Ex p. 85- Cl (35.45u), Br (81.18u), I (126.9u)
• Actual for Br 79.9u
• p. 86 Ca (40.08u), Sr (88.69u), Ba (137.3u)
• Actual for Sr 87.62u

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Dmitri Mendeleev (1869)

• Developed a periodic table of elements according
  to increasing atomic mass
• Elements were in vertical columns starting with
  the lightest
• Elements in horizontal rows displayed similar
  properties

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Dmitri Mendeleev (1869)

• He wrote question marks in places where unknown
  elements would eventually be placed (Mendeleev
  successfully predicted properties of most of the
  undiscovered elements)
•  Improved version later- patterns of changing
  properties repeated for elements across
  horizontal rows and elements in vertical columns
  showed similar properties
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• The repeated pattern is an example of
  periodicity.
• PERIODICTY Tendency to recur at regular
  intervals.

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Modern Periodic Table

• Each element has its own block with its name and
  symbol, atomic number and atomic mass
• Modern Periodic Table - p. 90-91
• English Chemist Henry Moseley (1913) Ordered by
  atomic number, not atomic mass

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Modern Periodic Table

• Atomic number is equal the number of protons in
  the nucleus
•  
• Atomic number increases by one as you move from
  element to element across a row
•  
• Properties of elements change in an orderly
  progression from left to right.

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PERIODIC LAW

• Physical and chemical properties of the elements
  repeat in a regular pattern (periodicity) when
  they are arranged in order of increasing atomic
  number is known as the