The Periodic Table: Organizing the Elements

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The Periodic Table Organizing the Elements

• OBJECTIVES
• Describe the origin of the periodic table.

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History

• By 1869, a total of 63 elements had been
  discovered.
• As the number of known elements grew, scientists
  began to recognize patterns in properties and
  began to develop classification schemes.

3
History

• Between 1817 and 1829 Johann Dobereiner
  discovered triads

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39

• Groups of similar elements
• The average of the top and bottom the middle
  element

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History

• John Newlands 1863-1864
• Law of Octaves elements repeated properties
  every 8th element

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History

• He had not known about the noble gases and some
  missing elements

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Dmitri Mendeleev

• Dmitri Mendeleev Russian chemistry teacher 1869
  
• Arranged elements in order of increasing atomic
  mass
• Placed elements on cards for each of the 63 known
  elements

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Dmitri Mendeleev

• He arranged the cards in order by mass
• He would start a new row each time a property
  repeated
• If a card did not match the elements in the next
  column, he made a new column
• He would also skip columns and leave gaps

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Dmitri Mendeleev
Notice how the elements that have the same
properties are in the same column.
N 14
P 31
C 12
F 19
Be 9.0
Cl 35
Na 23
O 16
Si 28
Li 6.9
Al 27
S 32
Ca 40
Mg 25
B 11
K 39
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Dmitri Mendeleev
When the next element in the sequence did not
match B and Al, he pushed the entire chart over
and created a gap.
Cr 52
V 50
Ti 48
Fe 56
Mn 55
Ni 58.7
Cu 64
Zn 65
Co 58.9
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Dmitri Mendeleev
B 11
C 12
O 16
F 19
N 14
As did not match Al or Si so he skipped the areas
under them, and went onto the N P group
Al 27
S 32
Cl 35
Si 28
P 31
As 75
Zn 65
Cu 64
Ni 58.7
Co 58.9
Fe 56
Br 80
Se 79
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Dmitri Mendeleev

• He predicted the presence of ten missing elements
• He described what they would be like
• They were later discovered and matched his
  predictions
• His chart was widely accepted

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Dmitri Mendeleev

• There were some elements that were out of order
  by mass
• He assumed the masses were wrong and followed his
  pattern of similar properties
• Examples are Ni and Co, K and Ar
• Find some for yourself.

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Modern Periodic Law

• Henry Moseley
• Discovered how to count the number of protons
  using X-ray diffraction
• Arranged elements according to increasing atomic
  number
• Solved the order problem for Mendeleevs table

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Modern Periodic Law

• When placed in order by the atomic number ( of
  protons), elements will periodically repeat
  physical and chemical properties

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Periodic table

• Horizontal rows periods
• There are 7 periods
• Periodic law
• Vertical column group (or family)
• Similar physical chemical prop.
• Identified by number letter

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Areas of the periodic table

• Group A elements representative elements
• Wide range of phys chem prop.
• Metals electrical conductors, have luster,
  ductile, malleable

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Metals

• Group IA alkali metals
• Group 2A alkaline earth metals
• Transition metals and Inner transition metals
  Group B
• All metals are solids at room temperature, except
  _____.

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Nonmetals

• Nonmetals generally nonlustrous, poor conductors
  of electricity
• Some gases (O, N, Cl) some are brittle solids
  (S) one is a fuming dark red liquid (Br)
• Group 7A halogens
• Group 0 noble gases

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Division between metal nonmetal

• Heavy, stair-step line
• Metalloids border the line
• Properties intermediate between metals and
  nonmetals
• Learn the general behavior and trends of the
  elements, instead of memorizing each element
  property