Valence Electrons and Lewis Dot Structures

1. Valence Electrons and Lewis Dot Structures We always have so much to do!

2. What is a Valence Electron? • Valence Electron: electron in the outermost energy level of an atom. • Are they more important than the rest?? • They’re the ones doing most of the movement during a chemical reaction. • So we’re going to need to know how many there are in an atom!

3. Finding Valence Electrons with the Periodic Table • It’s super easy! You’ll like it! • (For everything but Transition Metals in the Middle) • First step: find the element on the periodic table. • Second step: find the group number on the top of that column. (ignore the 1 in Groups 13-18) • Ta-Da! That’s it!

4. Yay Practice! • Find the # of valence electrons for: • Li • P • I • Ar • Ca • O = 1 = 5 = 7 = 8 = 2 = 6

5. What Atoms Like • Octet Rule: most atoms want to be surrounded by 8 valence electrons or 0 valence electrons. (It’s all or nothing)

6. Now For Lewis Dot Structures! • Easy, easy stuff! • Step 1: Write the symbol for the element. • Step 2: Put ‘dots’ around the symbol to represent valence electrons. • 1 dot = 1 electron • Ta-Da! That’s it!

7. “C” It In Action! • Let’s do Carbon. Carbon=C • Carbon is in Group 4 • = 4 valance electrons • Put one on each side!

8. Rules for filling in Dots • Maximum 2 dots per side (4 sides = 8 dots) • It does not matter which side you start on. • You have to fill in each side with one dot before you double up… • Example: Sulfur has how many valence e-? 6 How many dots does it get? 6 S

9. You do some! • Draw the Lewis Dot Structures for the following atoms: • Oxygen • Sodium • Fluorine • Nitrogen • Beryllium

10. Check It! O 1. Na 2. 3. F 4. 5. Be N

11. Now What Do I Do With That? • We can use number of valence electrons to predict which charge they have when we turn them into an ion. • What’s an ion?? • An atom that has gained or lost electrons. • Octet Rule: most atoms want to be surrounded by 8 valence electrons or 0 valence electrons. (It’s all or nothing)

12. How So? • For atoms with LESS than 4 valence electrons, they’re going to lose or give up electrons to form positive cations. • For atoms with MORE than 4 valence electrons, they’re going to gain or steal electrons to form negative anions. • For atoms with 4 valance electrons, it can go either way. • For atoms with 8 valance electrons, there is no change.

13. Why??? protons electrons

14. Example • I need to know what ion Aluminum forms. • I know that it has ____ valence electrons. • Is 3 closer to 0 or 8? • So will it gain or lose electrons? • How many will it lose to be 0? • If it loses electrons, will it be + or -? • So I end up with… Al+3 3 Closer to 0 Lose All 3 +

15. Remember This Chart!

16. More Practice! • Bet you knew that was coming, too, huh? • Predict the ion formed by the following elements: Write the symbol with the charge. • Cl • B • K • Ca • O • Ne

17. Check It! • Cl = Cl-1 • B = B+3 • K = K+1 • Ca = Ca+2 • O = O-2 • Ne = Ne or Ne0 (no change)