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The Periodic Table. 1868 Was organized according to the properties of the known elements Dmitri Mendeleev noticed that when the elements were put into order by their atomic mass, some of their properties repeated periodically. Dmitri Mendeleev.

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The periodic table
The Periodic Table

  • 1868

  • Was organized according to the properties of the known elements

  • Dmitri Mendeleev noticed that when the elements were put into order by their atomic mass, some of their properties repeated periodically


Dmitri mendeleev
Dmitri Mendeleev

  • Noticed that properties repeat, e.g. melting point, react with oxygen, density, mass…


Periodic table
Periodic Table

  • So he put them in columns with others that are similar.

  • Didn’t know anything about protons, electrons, etc. Just made observations!

  • Even made some guesses about ones that were missing and their properties. He was correct!


Guesses
Guesses

  • Eka-Aluminum:

    • Atomic Mass 68, density 5.9

  • Gallium (Ga):

    • Atomic mass 69.7, density 5.94

  • Eka-Silicon:

    • Atomic Mass 72, density 5.5

  • Germanium (Ge):

    • Atomic Mass 72.6, density 5.7


Atomic theory
Atomic Theory

  • Democritus …5th century

    BCE

  • Matter is made up of atoms

    • Atoms are solid

    • No internal structure

    • Different sizes

    • Space in between them (void)


Atomic theory1
Atomic Theory

  • John Dalton … 1800’s

  • Father of modern atomic theory

  • Discovered atomic weights and symbols for elements

  • elements made of atoms

  • atoms of an element same mass

  • different elements have different masses

  • Atoms combine in small, ratios such as 1:1, 1:2, 2:3

  • atoms can’t be created or destroyed


Atomic theory2
Atomic Theory

  • JJ Thompson … 1897

  • Discovered electron (first subatomic particle)

  • Believed atoms had negative charges floating in a sea of positive ones, like chocolate chips in a cookie

  • Called plum pudding

    model


Atomic theory3
Atomic Theory

  • Earnest Rutherford … 1911

  • Discovered nucleus of atom and said it was positive

  • Electrons orbit through empty space around positive nucleus


Atomic theory4
Atomic Theory

  • Niels Bohr … 1914

  • Discovered energy levels for electrons

  • Farther away from nucleus, higher energy level

  • Planetary model… like planets orbiting sun


Atomic theory5
Atomic Theory

  • Quantum theory

  • Current theory

  • Electrons don’t have orbits like planets

  • They move to fast to know exactly where they are, but we can tell where they probably are

  • Electron cloud is place where they probably are


Electron cloud
Electron cloud

  • Broken down into energy levels

  • Energy levels have sublevels called orbitals

  • Energy levels and orbitals only hold a certain number of electrons maximum

  • Called s p d f


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