Periodic Table

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Periodic Table

• This table is a remarkable way to show the
  manifold relationships between differing kinds of
  elements
• The modern table was devised in 1869 by Dimitri
  Mendeleyev
• He arranged the elements by weight and by their
  chemical properties

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Periodic Table

• "...if all the elements be arranged in order of
  their atomic weights a periodic repetition of
  properties is obtained." - Mendeleyev

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Periods and Groups

• Horizontal rows in the periodic table are called
  periods
• Vertical columns are called groups
• We will learn later why the elements can be
  arranged in this fashion based on the
  arrangements of the electrons outside the nucleus

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Periods and Groups

• Sizes of the atoms decrease as we move from left
  to right across a period
• This is due to the increasing number of protons
  in the nucleus, so the electrical attraction
  between the nucleus and the orbiting electrons
  gets stronger and pulls the electrons closer to
  the nucleus

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Periods and Groups

• We can display the table to demonstrate other
  properties as well
• As you move from left to right across a period,
  the ability of the atom to attract another
  electron increases
• This property is called electronegativity

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Periods and Groups

• All the elements in a column have remarkably
  similar chemical properties
• Some of the columns have been given special names
  to distinguish them
• The first group is called the alkali metals
• The second group is the alkaline-earth metals

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Periods and Groups

• Groups 3-12 are called the transition metals
• Groups 13-15 are not named
• Group 16 are the chalcogens
• Group 17 are the halogens
• Group 18 are the noble gases and are basically
  inert

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Lots of Questions

• Why are there only two elements in the first
  period?
• Why are there eight elements in the second and
  third periods?
• Why do we jump to eighteen in the fourth period?
• Why are the chemical properties of a group so
  similar?

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Lots of Questions

• Next time we will begin our studies of models of
  the atom
• Our goal will be to answer these questions
• This will take us into the realm of quantum
  mechanics
• We will see how the wave properties of the
  electrons provide the answers