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Writing Ionic Formulas

Writing Ionic Formulas. Ionic Compounds. Things you should know: Ionic = metal-nonmetal combo of elements Metal: loses e- to become stable; positive ions Nonmetal: gains e- to become stable; negative ions The charge value (1, 2, or 3) depends on how many e- were lost or gained.

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Writing Ionic Formulas

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  1. Writing Ionic Formulas

  2. Ionic Compounds • Things you should know: • Ionic = metal-nonmetal combo of elements • Metal: loses e- to become stable; positive ions • Nonmetal: gains e- to become stable; negative ions • The charge value (1, 2, or 3) depends on how many e- were lost or gained. • The # lost or gained was the # needed to be “full”.

  3. Predicting Charges on Ions KNOW THESE !!!! +1 +2 +3 -3 -2 -1 0

  4. Method One: electron dot diagrams • The # of dots shown = # of valence e-. • Column # = # of valence e-. • e- are gained or lost in the # needed for each atom/ion to be stable.

  5. e- dot diagrams for some common elements

  6. e- dot diagram for Potassium (K) e- dot diagram for oxygen (O) Transfer of e- to form potassium oxide Use e- dot diagrams to show the transfer of e- to make the metal and nonmetal atoms stable.

  7. Writing the Formula • If the ratio is 1:1, no subscript is needed. • Ex: sodium chloride = NaCl • If the ratio is NOT 1:1 use a subscript for each element which has more than 1 ion involved in the transfer. • Ex: potassium oxide = K2O

  8. Your Turn! • What is the formula of barium iodide? • Show the e- dot diagram of each element. • Show the transfer of e-. • Write the formula based on the ratio of the ions.

  9. e- dot diagram for Barium (Ba) e- dot diagram for iodine (I) Transfer of e- to form barium iodide Barium Iodide

  10. Formula • BaI2

  11. Ion charge for Aluminum (Al) Ion charge for chlorine (Cl) “Adding” the ions to get a neutral compound Method 2: using charges of the ions

  12. The formula • AlCI3

  13. Your Turn! • What is the formula of lithium sulfide? • Determine the ion charge of each element. • Determine the # of each ion needed to form a neutral compound. • Write the formula based on the ratio of the ions.

  14. The Formula • Li2S

  15. Transition Metals • Transition metals = B column elements • Charge can vary. It may be: +1, +2, +3, or +4. • A number in parentheses following the name of the metal gives the ion charge. • Ex: Iron (II) = Fe+2 Iron (III) = Fe+3

  16. Ion charge for Chromium (Cr) Ion charge for sulfide “Adding” the ions to get a neutral compound Teacher Example • What is the formula of chromium (III) sulfide?

  17. The formula • Cr2S3

  18. Your Turn! • What is the formula for silver (I) chloride?

  19. The formula • AgCI

  20. Polyatomic Ions • Not all ionic compounds are composed of metal and nonmetal elements. • What?!?! • All ionic compounds ARE composed of positive and negative ions. • Some ions are composed of 2 or more elements. • Poly = “many” Atomic = refers to atoms

  21. Polyatomic Ions-continued • = a group of atoms covalently bonded together that has a net charge. • Examples: NH4+ Ammonium C2H3O2- Acetate CN- Cyanide O22- Peroxide NO3- Nitrate NO2- Nitrite SO4-2 Sulfate SO3-2 Sulfite

  22. 1– Hydroxide Ion (OH-) O H Together, the group has a charge. Like a molecule, the O and H atoms stay bonded together and act as one particle.

  23. 1– ClO2- Chlorite Ion Cl O O One chlorine atom and two oxygen atoms covalently bonded, together carrying a 1- charge

  24. Writing a formula that contains a polyatomic ion • Use the charge method. “Adding” the charges of the ions, the compound must be neutral. • Compound: Magnesium hydroxide

  25. Ion charge for Magnesium (Mg) Ion charge for hydroxide (OH-) “Adding” the ions to get a neutral compound Magnesium hydroxide

  26. The formula • Mg(OH)2

  27. Your Turn! • Write the formula for lithium phosphate.

  28. The formula • LiPO4

  29. Ion charge for Chromium (Cr) Ion charge for sulfate “Adding” the ions to get a neutral compound Let’s Put It All TogetherTransitional metal and Polyatomic Ion • What is the formula of chromium (III) sulfate?

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