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Periodic Table History

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Periodic Table History. Dobereiner. He put elements with similar chemical properties together They went into in groups of 3 He noticed these trends in groups of elements such as:. Atomic Weight of “middle” element is average of other two – approx. Can you name these elements ?.

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dobereiner
Dobereiner
  • He put elements with similar chemical properties together
  • They went into in groups of 3
  • He noticed these trends in groups of elements such as:

Atomic Weight of “middle” element is average of other two – approx.

Can you name these elements ?

dobereiner s law of triads
Dobereiner’s Law of Triads
  • A triad is a group of three elements
  • with similar chemical properties in which
  • the atomic mass of the middle element is approximately equal to the average of the other two.
  • Only worked for very few elements of the 50 or so that were known at the time
  • BUT
  • He was first to make a link between atomic weight and properties
john newland
John Newland
  • Arranged the 60 known elements in order of increasing atomic weight
  • His pattern was…
  • Every 8th element was a repeat

(i.e. had 7 groups)

  • His Law was called…
law of octaves
Law of Octaves
  • An octave is a group of elements arranged in order of increasing atomic weight, in which the first and the eighth element of each group have similar properties.
  • The properties repeat every 8 as noble gases hadn’t been discovered yet!
  • Only worked for 17 out of 60 elements
  • There were several problems such as iron being grouped with oxygen and sulphur.
  • Laughed at but was basically correct
mendeleev
Mendeleev
  • Arranged the known elements in order of increasing atomic weight
  • His Law was called…
mendeleev s periodic law
Mendeleev’s Periodic Law:
  • When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements vary periodically.
mendeleev1
Mendeleev:
  • Put elements with the same properties in the same vertical group.
  • Reversed the order of some elements (Te/I) so that their properties matched their group.
  • Left gaps to make the elements fit into the proper column (group).
  • Predicted that elements (eg. Germanium and Gallium) would be discovered to fill these gaps. Predicted their properties correctly.
mendeleev s modern periodic table v periodic table
Gaps left for undiscovered elements

Group 0 elements missing

Elements discovered since 1869 missing

D-block elements arranged as subgroups beside each main group

Elements arranged in order of increasing atomic weight in almost all cases.

Gaps have been filled

Group 0 elements included

Elements discovered since 1869 included

D-block elements arranged as subgroups in a separate block

Elements arranged in order of increasing atomic number

Mendeleev’s Modern Periodic Table V Periodic Table
moseley atomic number
Moseley – Atomic Number
  • The atomic number of an atom is the number of protons in the nucleus of that atom.
  • Moseley used x-rays to find out how much positive charge each nucleus had
  • In other words the difference between the elements is the number of protons in the nucleus.
  • Once the atomic number was known it was seen that Mendeleev’s table was in order of increasing atomic number – not weight.
modern periodic table
Modern Periodic Table
  • In order of increasing atomic number.
  • There were 63 elements in Mendeleev’s table – now 109
  • No gaps
  • The transition elements are listed separately.
  • Today’s table 1940 – Glenn Seaborg
do i know it
Do I know it???
  • Who proposed Law of Triads?
  • Who proposed Law of Octaves?
  • Who proposed Periodic Law?
  • Can I explain each ?
  • Can I name 3 triads?
  • What was Moseley’s contribution to the Periodic Table development?
  • Four differences between Mendeleev’s Table and modern table?
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