1. Electrons and Energy Levels An atom is the smallest particle into which an element can be divided and still be that element. Is this accurate?

2. Electrons and Energy Levels There are many different energy levels electrons can hold within the atom. The number of filled energy levels depends on the number of electrons. Electrons fill the energy levels closest to the nucleus first. Energy levels are called Shells

3. Electron Shells Electrons are arranged around the Nucleus in SHELLS. For simplicity they can be thought of like mini-planets orbiting a central sun, but it is closer to the truth to think of them as "clouds" of electric charge around the Nucleus.

4. Electron Shells The shells are numbered outward from the Nucleus. The maximum number of electrons found in each shell can be calculated by: 2n 2 where "n" is the number of the shell. Shell # Maximum Number of Electrons in the Shell 12 x 1 = 2 22 x 4 = 8 32 x 9 = 18 42 x 16 = 32 52 x 25 = 50

5. For example: Sodium has an Atomic Number of 11 and an Mass Number of 23.

6. Example 2: Chlorine has a Mass Number of 35.5 and an Atomic Number of 17.

7. Example 2: Chlorine has a Mass Number of 35.5 and an Atomic Number of 17.

8. Orbitals & Energy Levels Within each Shell are orbitals or sub levels. An Orbital is a region in an atom where there is a high probability of finding an electron There are 7 kinds of orbital: They are labeled s, p, d, f, g, h, and i.

9. Orbitals or Sublevels Letter Maximum number of electrons in shell s2 p6 d10 f14 g18

10. Electron Sublevels 1s 2 =2 2s 2 2p 6 =8 3s 2 3p 6 3d 10 =18 4s 2 4p 6 4d 10 4f 14 =32 5s 2 5p 6 5d 10 5f 14 5g 18 =50 6s 2 6p 6 …

11. Sublevel Order 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 7s 2 5f 14 6d 10 7p 6 8s 2 5g 18 6f 14 7d 10 8p 6

12. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 5f 14 5g 18 6s 2 6p 6 … 7s s 7p 6 … Arranging Sublevels

13. Valence electrons Valence electrons are all those electrons in the outermost electron shell, that is, in the shell with the highest shell number.

14. Valance Electron examples Determine the valence electrons present in atoms of each of the following elements. a) Ne b) Mg c) Cl

15. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 5f 14 5g 18 6s 2 6p 6 … 7s s 7p 6 … a) Ne Neon has 10 electrons total 1S 2 2S 2 2P 6

16. b) Mg The element magnesium has two valence electrons.

17. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 5f 14 5g 18 6s 2 6p 6 … 7s s 7p 6 … b) Mg 1s 2 2s 2 2p 6 3s 2 Magnesium has 12 electrons

18. A shortcut! [Ne] 3s 2 Write the noble gas, then write the sublevels.

19. B) Cl The element chlorine has seven valence electrons.

20. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 5f 14 5g 18 6s 2 6p 6 … 7s s 7p 6 … b) Cl 1s 2 2s 2 2p 6 3s 2 3p 5 Chlorine has 17 electrons

21. Practice: Determine the number of valence electrons present in atoms of the following elements. a) Cb) S c) Brd) Li e) Caf) K g) He