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Topic: Writing Binary Ionic Formulas Do Now: An atom of which element has the greatest attraction for electrons in a chemical bond? A.As B. Ga C.Ge D.Se.

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Presentation on theme: "Topic: Writing Binary Ionic Formulas Do Now: An atom of which element has the greatest attraction for electrons in a chemical bond? A.As B. Ga C.Ge D.Se."— Presentation transcript:

1 Topic: Writing Binary Ionic Formulas Do Now: An atom of which element has the greatest attraction for electrons in a chemical bond? A.As B. Ga C.Ge D.Se

2 Empirical Formulas = smallest whole-number ratio of elements in compound Ionic compounds have empirical formulas only

3 Identify the empirical formulas H 2 O H 2 O 2 CaF 2 NaCl CH 4 C 2 H 6 NiO FeCl 3 Empirical – NOT ionic Molecular – NOT ionic Empirical, Ionic Empirical – NOT ionic Molecular – NOT ionic Empirical, Ionic

4 Formula Unit = simplest ratio of ions in ionic compound Examples: KBr is formula unit –potassium ions & bromide ions are in a 1-to-1 ratio Al(NO 3 ) 3 is formula unit –Aluminum & nitrate ions in 1-to-3 ration

5 Binary Ionic Compounds Composed of two different elements –Positive monatomic metal ion –Negative monatomic nonmetal ion Note: A binary compound may contain more than 2 ions but only 2 kinds of ions like Al 2 O 3

6 Oxidation Number or State charge of monatomic ion has right superscript Some elements form only 1 ion Some elements can form more than 1 ion Ca +2 Na +1 O -2 Fe +2 and Fe +3 Al +3 and Ag +1

7 Oxidation States Group 1 ions always +1 Group 2 ions always +2 MOST group 13 ions are +3 Groups 14, 15, 16, and 17 have multiple oxidation states –both (+) and (-) Transition metals (Group B) can have more than 1 oxidation state – but are always (+)

8 Writing Formulas for Binary Ionic Compounds first rule in writing formulas for ionic compounds is POSITIVE ION FIRST But how do you get the subscripts? start by writing formulas from the ions

9 Compounds are electrically neutral – Sum of all charges in compound should be 0 – (+) and (-) charges must = each other

10 Equal but Opposite Charges Na +1 and Cl -1 : NaCl +1 + (-1) = 0 Mg +2 and O -2 : MgO +2 + (-2) = 0 Al +3 and P -3 : AlP+3 + (-3) = 0 FIRSTRule: write symbols, (+) FIRST!

11 Try a few formulas: Li +1 and I -1 Ca +2 and O -2 Al +3 and N -3 K +1 and F -1 Ba +2 and S -2LiI CaO AlN KF BaS

12 Criss-Cross Method When the charges don’t cancel out immediately: CROSS and DROP!Mg +2 and Cl -1, CROSS and DROP! (# only, forget signs!) (# only, forget signs!) Mg 1 Cl 2 but if subscript is 1, forget it! MgCl 2 means 1 Mg +2 and 2 Cl -1

13 Check the Math MgCl 2 means 1 Mg +2 and 2 Cl -1 (1 x +2) + (2 x -1) = = 0 charges MUST add up to zero!

14 Try a few formulas: Ca +2 + Cl -1 Na +1 + O -2 Cs +1 + S -2 Al +3 + Cl -1 Al +3 + Se -2 Mg +2 + F -1 K +1 + N -3 CaCl 2 Na 2 O Cs 2 S AlCl 3 Al 2 Se 3 MgF 2 K3NK3NK3NK3N

15 Of course, it gets more difficult Potassium (K) and Fluorine (F) Zinc (Zn) and Iodine (I) Sodium (Na) and Oxygen (O) Magnesium (Mg) and Oxygen (O) Aluminum (Al) and Oxygen (O) Calcium (Ca) and Bromine (Br) Cesium (Cs) and Iodine (I) Silver (Ag) and Sulfur (S)KF Na 2 O MgO Al 2 O 3 CaBr 2 CsI ZnI 2 Ag 2 S


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