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Writing Formulas Oxidation Numbers & Chemical Formulas Mrs. Wolfe
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Review: How do you figure out the charge of an ion? What is the charge of Sodium? +1 Another word for Charge is OXIDATION NUMBER. + -
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Is there a pattern of Oxidation Numbers on the Periodic Table? Time for a Worksheet: “Discovering Oxidation Numbers”!
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+1 +2+3±4-3-2 0 Write the pattern in your notes!
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There is a pattern of ions! METALS ARE POSITIVE! NONMETALS ARE NEGATIVE!
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Practice Problems… What is the oxidation number of Aluminum? +3 What is the oxidation number of Iodine? Time for a worksheet: Oxidation Numbers
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Writing Formulas Consider the formula BeCl 2 How many atoms of Beryllium are in that compound? 1 How many atoms of Chlorine? 2 WHY?
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BeCl 2 Be 2 Cl 7 7
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Cl -1 BeCl 2 Be +2 Cl -1 Be +2
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Lithium & Fluorine What is the oxidation number for Lithium? +1 Fluorine? So how many atoms do you need of each element to make a compound? One of each! The formula is… LiF F -1 Li +1
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LiF not FLi…why? You always write the METAL FIRST in a formula. Let’s try another one. Try to write a formula for Magnesium & Sulfur. MgS S -2 Mg +2
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How about Magnesium + Chlorine? Magnesium’s oxidation # +2 Chlorine’s oxidation # Cl -1 Mg +2 Cl -1 MgCl 2 Time for some practice with Formula Writing!
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