1. Electrons & their arrangement in an atom

2. Electrons live in something called energy levels. Only so many electrons can be in any energy level. The electrons in the outer most energy level of any element are called valence electrons. Electrons have special rules….

3. Bohr Diagrams 1)Find the element on the periodic table. 2) Determine the number of electrons– in a neutral atom it is the same as the atomic number. 3) This is how many electrons you will draw.

4. Bohr Diagrams Find out which period (row) your element is in. Elements in the 1 st period have one energy level. Elements in the 2 nd period have two energy levels, and so on. 1 2 3 4 5 6 7

5. The electron shells surrounding the nucleus each hold a particular number of electrons. Shells are named with letters: 1 = K shell = 2 electrons 2 = L shell = 8 electrons 3 = M shell= 8 electrons 4 = N shell= 18 electrons 5-7 = O, P, Q= up to 32 electrons Remember: The outer shell of an atom (no matter what letter) can only hold 8 electrons!

6. Bohr Diagrams 1) Draw a nucleus with the element symbol inside. C 2)Write the number of Protons the element has inside the nucleus. P = 6

7. Bohr Diagrams 1)Carbon is in the 2 nd period, so it has two energy levels, or shells. 2)Draw the shells around the nucleus. C P = 6

8. Bohr Diagrams 1) Add the electrons. C P = 6 2 e- 2)Carbon has 6 electrons. 3)The first shell can only hold 2 electrons. 4)Write the number of electrons that shell holds and e- for electrons and their charge. 5)How many electrons are in the outer shell?

9. Bohr Diagrams 1) Since you have 2 electrons in the first shell, you need to add 4 more. C P = 6 2)These go in the 2 nd shell. 3)Again, write e- and the number of electrons. 2e- 4e-