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Valence Electrons and Lewis Dot Structures We always have so much to do!
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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!!
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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!
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Yay Practice! Find the # of valence electrons for: 1.Li 2.P 3.I 4.Ar 5.Ca 6.O
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Check with your Buddy Compare answers to ONE person next to you!
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Check It! 1.Li=1 2.P=5 3.I=7 4.Ar=8 5.Ca=2 6.O=6
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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)
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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.
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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 0 Lose + All 3
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Remember This Chart?
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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.Cl 2.B 3.K 4.Ca 5.O 6.Ne
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Check with your Buddy Compare answers to ONE person next to you!
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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)
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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!
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See It In Action! Let’s do Carbon. Carbon=C Carbon is in Group 4 = 4 valance electrons Put one on each side!
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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
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You do some! Draw the Lewis Dot Structures for the following atoms: 1.Oxygen 2.Sodium 3.Fluorine 4.Nitrogen 5.Beryllium
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Check with your Buddy Compare answers to ONE person next to you!
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Check It! 1. 2. 3. 4.5. O Na F N Be
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So Easy, Right? The end. Quiz on this stuff next class so don’t forget everything!
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