Valence Electrons and Lewis Dot Structures

We always have so much to do!

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?– Indeed you are!!

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!

• Can we practice??– Absolutely!

Yay Practice!

• Find the # of valence electrons for:

1. Li

2. P

3. I

4. Ar

5. Ca

6. O

Check with your Buddy

• Compare answers to ONE person next to you!

Check It!

1. Li = 1

2. P = 5

3. I = 7

4. Ar = 8

5. Ca = 2

6. O = 6

Now What Do I Do With That?

• We can use number of valence electrons to predict which charge they make when we turn them into an ion.

• Pop Quiz: what’s an ion??– An atom that has gained or lost electrons.

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

How So?

• For atoms with LESS than 4 valence electrons, they’re going to lose/give up electrons to form positive cations.

• For atoms with MORE than 4 valence electrons, they’re going to gain/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.

Example

• I need to know what ion Aluminum forms.• I know that it has 3 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

Closer to 0Lose

+

All 3

Remember This Chart?

More Practice!

• Bet you knew that was coming, too, huh?• Predict the ion formed by the following

elements: Write the symbol with the charge.1. Cl2. B3. K4. Ca5. O6. Ne

Check with your Buddy

• Compare answers to ONE person next to you!

Check It!

1. Cl = Cl-

2. B = B+3

3. K = K+

4. Ca = Ca+2

5. O = O-2

6. Ne = Ne (no change)

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.

• Ta-Da! That’s it!

See It In Action!

• Let’s do Carbon. Carbon=C

• Carbon is in Group 4

• = 4 valance electrons

• Put one on each side!

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

You do some!

• Draw the Lewis Dot Structures for the following atoms:

1. Oxygen

2. Sodium

3. Fluorine

4. Nitrogen

5. Beryllium

Check with your Buddy

• Compare answers to ONE person next to you!

Check It!1. 2. 3.

4. 5.

O Na F

N Be

So Easy, Right?

• The end.

• Quiz on this stuff next class so don’t forget everything!