2. Atomic Theory History
Dalton Thomson Rutherford Bohr
If the nucleus of an atom is positively charged, and there are negatively charged electrons going around it, why do the electrons not crash into the nucleus?

3. Niels Bohr (1913)
Niels Bohr experimented with gas discharge tubes and came up with an explanation of why different elements produced different colours.

4. Electrons must occupy orbits (sometimes called orbitals, or energy shells.
Electrons stay in their orbits, unless they are excited by electricity or heat. If that happens, they can jump to another orbit.
When they return to their original orbit, they give off a specific wavelength of light.

5. Bohr-Rutherford Diagram Rules
This is a representation of the atom that shows the number of protons in the nucleus, as well as the number of electrons in each orbit.
A maximum of 2 electrons can fit in the first orbit.
A maximum of 8 electrons can fit in the second orbit.
A maximum of 8 electrons can fit in the third orbit.

6. VERY IMPORTANT TIP:
The atomic number of an element shows you how many protons and electrons there are (# of protons = # of electrons).

7. Important Additional Rule:
If an atom has 9 electrons, can they be distributed randomly into any of its orbitals?
An orbital must be filled to capacity with electrons before we begin to assign electrons to another orbital.

8. Steps to drawing Bohr-Rutherford Models Ex: Mg
Draw a circle to represent the nucleus. Write in the element’s symbol, and how many protons it has using the symbol p+. (Leave lots of space around the nucleus) Mg
12 p+
Remember!
Number of protons = Number of electrons = atomic number

9. Steps to drawing Bohr-Rutherford Models Ex: Mg
Draw an orbital and begin to distribute all the electrons. You must fill an orbital completely before starting a new one. In this case, we have 12 electrons to distribute.
Remember: 1st orbit: Max of 2 electrons
2nd orbit: Max of 8 electrons
3rd orbit: Max of 8 electrons
1st orbit filled: 10 electrons left Mg
12 p+

10. Steps to drawing Bohr-Rutherford Models Ex: Mg
Draw an orbital and begin to distribute all the electrons. You must fill an orbital completely before starting a new one. In this case, we have 12 electrons to distribute.
Remember: 1st orbit: Max of 2 electrons
2nd orbit: Max of 8 electrons
3rd orbit: Max of 8 electrons
10 electrons distributed, 2 left Mg
12 p+

11. Steps to drawing Bohr-Rutherford Models Ex: Mg
DNE! Mg
12 p+

12. Review of Bohr-Model

14. Lewis structures
Lewis structures only show the valence electrons of an atom.
Place electrons one by one around the symbol of the atom like the points on a compass.

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16. The staircase line separates metals and non-metals
The staircase line separates metals and non-metals. Everything to the left of the staircase line is a metal (except Hydrogen) and everything to the right is a non-metal.

17. Periodic Table Information

18. Periodic Table Information
Columns in the table are called groups. They tell you how many valence electrons there are.
Periodic Table Information

19. Periodic Table Information
Rows in the table are called periods. They tell you how many orbitals there are.
Periodic Table Information