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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Periodic Table History

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Periodic table history

Periodic Table History


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 VPeriodic Table


Mendeleev s table

Mendeleev’s 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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