What is the periodic table?

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What is the periodic table?
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Learning Objective

• Students will trace the development of the modern
  periodic table of elements.
• Students will understand the systematic
  organization of the periodic table.

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Key Terms

• group
• periodic
• period
• chemical symbol
• reactive

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Chemical Symbols

• For many years, scientists had to spell out the
  names of all the known elements.
• However, in the early 1800s, a Swedish scientist
  named Jons Jakob Berzelius created a new system
  of representing elements.
• This system uses letters called chemical symbols.
  
• Chemical symbols are a shortened way of writing
  the names of elements.

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Chemical Symbols- contd

• Chemical symbols are created from the name of
  each element.
• There are usually one or two letters in a
  chemical symbol.
• The first letter of a chemical symbol is always
  capitalized.
• If there is a second letter, it is written using
  the lowercase.
• Some elements have three letters in
• their chemical symbols.
• These chemical symbols are
• temporary until scientists come to
• an agreement on their
• permanent names.

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Arranging Elements

• By the 1800s, scientists had discovered many
  elements.
• They began to search for ways to organize these
  elements.
• In 1869, a Russian chemist named Dmitri Mendeleev
  listed the elements in order of increasing atomic
  mass.

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• He noticed that elements with similar properties
  occurred periodically.
• The word periodic means "to repeat in a certain
  pattern."
• Based on the pattern he observed, Mendeleev
  arranged the elements in rows in a chart.
• Elements with similar properties
• were in the same column of his
• chart, one under the other.
• Mendeleev's chart was the first
• periodic table of elements.

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The Modern Periodic Table

• Mendeleev's periodic table had some problems.
• Some elements did not have properties similar to
  the other elements in the same column.
• The discovery of atomic numbers, 50 years later,
  by Henry Moseley led to a new table.
• Arranging the elements in order
• of increasing atomic number
• instead of increasing atomic mass,
• all the elements in the same
• column had similar properties.
• This new arrangement is the modern
• periodic table of elements.

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Periodic Law

• The periodic law states that the physical and
  chemical properties of the elements are periodic
  functions of their atomic numbers.

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Periods

• The periodic table has seven rows.
• Each horizontal row is called a period.
• You can see that Period 1 has only two elements,
  hydrogen and helium.
• The elements in a period do not have similar
  properties.
• In fact, the properties of each
• element in a period change
• greatly as you move from left to
• right.

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Periods - contd

• However, there is a pattern as you move across a
  period from left to right.
• The first element in a period is a very active
  solid and the period ends with an element that is
  a very inactive gas.
• The first period is the only exception.

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1st period
2nd period
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Checking Concepts

• How is the first letter of a chemical symbol
  written?
• What are the horizontal rows of the periodic
  table called?
• How are the elements arranged in the modem
  periodic table?

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Answers

• As a capital letter
• Periods
• By increasing atomic number

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Groups

• When a column goes from top to bottom, it's
  called a group.
• There are 18 groups in the periodic table.
• Element within the same group have similar, but
  not identical properties. For example, lithium,
  sodium, potassium and the other members of the
  1st group are silver-white shiny metals.

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Map of Elements

• The periodic table is like a map of the elements.
• The position of the element tells about its
  properties.
• The elements position also tells how reactive it
  is (how likely it is to undergo a chemical
  change)
• The Periodic Table has 3 main
• regions
• Metals on the left (except H which is a
  non-metal)
• Non-metals on the right (except H which is
  located in the metals)
• Metalloids in the middle

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Metals .
Elements that conduct electricity and heat well
and have a shiny appearance
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Alkali Metals

• Group 1
• Very reactive
• Include sodium and potassium

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Alkaline Metals

• Group 2
• More reactive than all metals except Alkali
  metals
• Includes Calcium and Magnesium

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Transition Metals

• Group 3-12
• Includes copper, gold, silver and iron.
• Less reactive than most other metals.
• Used to make jewelry and coins because they dont
  react
• Sometimes found in foods
• Important in industry and technology.
• Often combined to form alloys .

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Rare Earth Metals

• Metals shown on the top row of the two rows shown
  on the outside of the main body of the periodic
  table.
• Referred to as Lanthanides
• Hard to isolate in a pure form

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Rare Earth Metals - Continued

• Actinides
• Radioactive and some are not found in nature.
• Some of the elements with higher atomic numbers
  have only been made in labs.

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Non-metals

• Properties are opposite of metals
• Most are gases
• Poor conductors of heat and electric current
• Includes nitrogen and oxygen
• 2 groups are halogens and noble gases

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Halogens

• Found in group 17
• Very reactive that form compounds called salts
  with many metals
• Used to kill harmful organisms
• Includes chlorine and iodine

Noble Gases

• Found in Group 18
• Almost never react with other
• elements
• Include Neon, Krypton and Argon
• Always a Gas

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Metalloids

• These elements have properties of both metals and
  nonmetals.
• Most common metalloid is silicon
• Used to make semiconductors found in electronics