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Q/ A. How would a compound form when Lithium is combined with Phosphorous? How many atoms of each would their be ? How would we write this out at a compound ? P -3 valence, Li +1 valence It would take 3 Li to complete the outer shell of P. Li 3 P. Writing Formulas for Ionic Compounds.

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Q/ A

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  1. Q/ A • How would a compound form when Lithium is combined with Phosphorous? How many atoms of each would their be ? How would we write this out at a compound ? • P -3 valence, Li +1 valence • It would take 3 Li to complete the outer shell of P. • Li3P

  2. Writing Formulas for Ionic Compounds 5.8

  3. What is the formula for the ionic compound formed by calcium and iodine? • Step 1- write the symbol of the metal or positively charged ion first. The symbol of the nonmetal or negatively charged ion is written second. Ca I

  4. Step 2- Write the charge of each element above each symbol. 2+ 1- Ca I • Step 3- Determine how many ions of each type you need so that the total ionic charge is zero. 2+ 1- Ca I One Ca2+ ion will balance the charge of TWO I- ions.

  5. Step 4- write the formula using subscripts to indicate the number of ions of each type. CaI2

  6. Crisscross rule • First you need to write the ionic charges above their symbols. • Ex: 3+ 2- Al S Then you need to ‘crisscross’ the charges, using them now as subscripts.

  7. Ex: 3+ 2- Al S • Now that we’ve crisscrossed the charges, add the subscripts. • Al2S3

  8. Crisscross Modified • The following is an example of when we have to modify the crisscross rule. • What is the formula for the ionic compound formed by nickel and oxygen ? • First, write the symbols. • Ex: Ni O

  9. Next write the ionic charges above the symbols, and crisscross them. • Ex: 2+ 2- Ni O Using the Crisscross rule, you should get Ni2O2. But why don’t we write this compound this way?

  10. Our formulas have to have the lowest number of ions that will produce an electrically neutral compound. So we divide by the common factor, in this case 2. • So, the formula for Ni and O = NiO

  11. Now try it the crisscross rule for this compound. • Sn combining with O. • +4 -2 Sn O

  12. Sn2 O4 • But what can we do ? • Divide by the common factor 2. • Making the compound: SnO2

  13. Questions 1) a) How do metals form ionic compounds with nonmetals? B) Describe this process with an example. 2) Beryllium and fluorine react to form an ionic compound. A) Which element is the metal and which is the nonmetal? B) How many electrons must each element gain or lose to form stable ions? C) Draw a lewis dot diagram of this compound. D) Indicate the ionic charges on the ions. E) What is the overall charge on the compound? F) What is the chemical formula?

  14. Questions from pg. 189 1-4 • 1 a) They form by the metal giving away valence electrons, and the non-metal taking the valence electrons. • 1b) NaCl- Na gives one, Cl takes one. • 2 a) Be = metal, F= non-metal. • B) Be= lose 2, F= gain one • D) Be= +2, F= -1 • E) Neutral • BeF2

  15. Brain Pop http://www.brainpop.com/science/matterandchemistry/chemicalequations/

  16. Q/A • Sodium and Nitrogen are combining to make a compound. Write it first as a balanced chemical compound. Second, name the compound.

  17. 1+ 3- Na N Use the crisscross rule: Na3N Naming the compound: Sodium Nitride

  18. Writing Compounds • When writing out the name of Ionic Compounds you have to: • Write the name of the metal first- always as it appears on the periodic table. • Write the name of the non-metal second, but add the ending ‘ide’. • Ex: CaI = Calcium Iodide

  19. Name of Element Symbol Charge Name of Compound • Fluorine F 1- Fluoride • Chlorine Cl 1- Chloride • Bromine Br 1- Bromide • Oxygen O 2- Oxide • Sulfur S 2- Sulfide • Nitrogen N 3- Nitride

  20. More than One Ionic Charge • Some metals can have two completely different ionic charges. • Ex: Copper. • Copper in white form = 1+ charge • Compound= CuCl • Copper in yellow form= 2+ charge • Compound= CuCl2

  21. So…. Add roman numerals • When you have elements that can make more than one ion, you need to show which ion they are forming with roman numerals. • Ex. CuCl = Copper (I) Chloride • Ex. CuCl2 = Copper (II) Chloride • You will be able to know which roman numeral to use by the neutral compound’s subscripts. • ONLY USE THIS WHEN THE ELEMENT CAN HAVE MORE THAN ONE IONIC CHARGE!

  22. Name of Element Symbol Ionic Charges Roman Numeral • Copper Cu 1+, 2+ I, II • Iron Fe 2+, 3+ II, III • Lead Pb 2+, 4+ II, IV • Tin Sn 2+, 4+ II, IV

  23. Changing from Words to Chemical Symbols • The last thing we need to understand is how to change compound names back into chemical formulas. • Ex: Magnesium Oxide • What do you think we do first ? • Magnesium= metal. Find it on the periodic table. Write it down with the charge. 2+ Mg

  24. What do we need to do second? • Oxide= Oxygen, a non-metal. Find it on the periodic table and write down the charge. 2- O

  25. Now put them together, and complete the criss cross rule. • 2+ 2- Mg O Mg2 O2

  26. There is a common factor, so we can simplify it to: MgO

  27. Q/A • Change the name compound of Sodium Iodide, into a chemical formula. • Na =+1 • I = -1 • NaI

  28. Handout • Part A • From the chemical formula, write the name • Part B • From the name, write the chemical formula

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