The Periodic Table

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The Periodic Table

• Part One

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• Elements are like a collection
• As more and more elements were discovered it
  became more important to organize and classify
  them

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The Basics

• What does periodic mean?
• Having or marked by repeated cycles
• What things in our everyday life do we notice as
  cyclic or periodic?

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Dmitri Meldeleev

• Russian scientist
• Published first USEFUL periodic table
• Did not know atomic structure, so he arranged
  atoms by mass
• Noticed a repeating pattern periodic

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Mendeleevs Periodic Table

• Spaces left for missing elements
• Were later discovered

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• Mendeleevs table was widely accepted because it
  predicted the existence and properties of
  undiscovered elements
• He also left blank spaces on the table for
  elements not yet discovered.
• Predicted properties of yet to be discovered
  elements such as scandium, gallium, and germanium

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But there were problems

• As new elements were discovered and atomic masses
  were more accurately determined, some elements
  with different properties were grouped together

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Henry Moseley (1913)

• English Chemist
• Figured out the problem with Mendeleev's Table
• What did Moseley Discover before?
• Atoms of each element contain unique number of
  protons in their nuclei
• He arranged elements in order of increasing
  atomic number and not increasing atomic mass

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Problem Solved!

• Moseleys arrangement solved the problems with
  Mendeleevs table
• His arrangement resulted in clear periodic
  patterns of properties
• Lead to Periodic Law
• Statement that there is a periodic repetition of
  chemical and physical properties of the elements
  when they are arranged in increasing atomic number

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Classes of elements

• Remember that elements are classified according
  to their properties as
• Metals
• Nonmetals
• Metalloids

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1. Metals

• Most elements are metals (everything on the left
  of the zigzag line on the periodic table)
• Elements that are shiny, smooth and clean
• Solid at room temperature
• Good conductors of heat and electricity
• Malleable
• Hammered flat into a sheet
• Ductile
• Drawn out into a wire

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2. Nonmetals

• The right side of the zigzag line on the periodic
  table
• Mostly gases
• Opposite of metals
• Brittle, dull-looking solids
• Poor conductors of heat and electricity
• Bromine (Br) is the only nonmetal that is liquid
  at room temperature

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3. Metalloids
Shiny brittle

• Elements that border the zigzag on the periodic
  table
• Called semiconductors
• Some properties of metals and some of non metals

Hard brittle
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What does the table tell us?

• Physical and chemical properties
• You can also predict what other elements a
  particular element will react with

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Whats in the box?

• Each square on the periodic table contains
  information about an element
• Name
• Chemical symbol
• Atomic number
• Atomic mass

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Whats in the box?

• What does the C stand for?
• Chemical symbol
• Carbon
• Usually consists of one or two letters.
• The first letter is always capitalized
• The second letter is always lowercase
• Names come from many sources and languages
• Scientists, geographical regions etc.

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Whats in the box?

• What does the 6 stand for?
• Atomic Number
• This tells us what about an atom of C?
• of protons
• What does the 12.011 stand for?
• Atomic Mass
• This tells us what about an atom of C?
• Mass in nucleus ( of protons and neutrons)

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What does the arrangement of the periodic table
tell us?

• The periodic table arranges the elements into
  columns and rows based on physical and chemical
  similarities.

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Periods

• Horizontal rows
• The properties of elements in a row follow a
  repeating, or periodic, pattern as you move
  across the table.
• The physical and chemical properties, such as
  conductivity and the number of electrons in the
  outer level of atoms, change gradually as you
  move from metal to nonmetal.

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Periods
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Periods

• The first element in a period is always an
  extremely reactive solid (with the exception of
  hydrogen), which means the readily combine with
  other elements.
• The last element in a period is a very inactive
  gas.

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Groups
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Groups

• There are 18 main columns of elements.
• Columns of elements are called groups or
  families.
• Elements within the same group or family have
  similar, but not identical properties.
• For example, all the elements of Family 1 are
  soft, white, shiny metals that are highly
  reactive.

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