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Understanding Ionic Compounds: Formulas, Prediction, and Polyatomic Ions

This guide provides a comprehensive overview of ionic compounds, focusing on the essentials of writing formulas, predicting ion charges, and understanding polyatomic ions. Learn about the formation of stable ions through electron transfer between metals and nonmetals. Discover methods for creating electron dot diagrams, utilizing charge values for metals, and incorporating polyatomic ions into compounds. Practice writing formulas for various compounds, ensuring they are neutral, and gain a firm grasp of the essential principles in chemistry related to ionic bonds.

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Understanding Ionic Compounds: Formulas, Prediction, and Polyatomic Ions

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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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