The Periodic Table

1. 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

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

3. 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!

4. 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

6. 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)

7. 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

8. 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

9. Atomic Theory • Earnest Rutherford … 1911 • Discovered nucleus of atom and said it was positive • Electrons orbit through empty space around positive nucleus

10. Atomic Theory • Niels Bohr … 1914 • Discovered energy levels for electrons • Farther away from nucleus, higher energy level • Planetary model… like planets orbiting sun

11. 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

12. 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