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Chemical compounds

Chemical compounds. Types Formulas Names. Learning objectives. Describe the octet rule Predict number of valence electrons on atom Predict ionic charges Predict composition of simple ionic compounds Predict which element combinations result in covalent bonding

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Chemical compounds

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  1. Chemical compounds Types Formulas Names

  2. Learning objectives • Describe the octet rule • Predict number of valence electrons on atom • Predict ionic charges • Predict composition of simple ionic compounds • Predict which element combinations result in covalent bonding • Describe difference between ionic and covalent bonds • Describe differences between ionic and covalent compounds

  3. Compounds rather than elements • Most atoms are more stable when bonded to other atoms • Compounds contain two or more elements • Distinguish between ionic compounds and molecular compounds

  4. Ionic versus molecular • Ionic compounds • Consist of ions (NaCl) • Always metal + nonmetal • Infinite lattice • Molecular compounds • Consist of molecules (CO2) • Finite size • Always nonmetals or metalloids

  5. Electrolytes and nonelectrolytes • An electrolyte is something that conducts electricity in solution – produces ions • All soluble ionic compounds are electrolytes • Molecular compounds except acids and bases are nonelectrolytes

  6. Electrolyte and nonelectrolyte • Ionic compound in solution produces ions - is an electrolyte • Molecular compound in solution as molecules – is nonelectrolyte (or weak electrolyte in some cases)

  7. Ionic compounds always contain a metal and a non-metal

  8. Comparing properties

  9. Rules to predict ion charge • Cation • Charge = group number • Anion • Charge = - (8 - group number) • Practice with a few examples

  10. Composition depends on ionic charge (group number) • Charges must balance: compounds are neutral – ions are charged • Total cation charges = total anion charges • One Ca2+ two F-

  11. Brief introduction to formulae • Overall charge must be neutral • Formula contains metal ion first, nonmetal ion second • Coefficient of metal = charge on nonmetal • Coefficient of nonmetal = charge on metal • x and y are shown with lowest common denominator in most cases. Calcium oxide is CaO not Ca2O2 y+ x- A B x y

  12. Polyatomic ions • Group of atoms with an ionic charge • Usually different elements • Except O22- or Hg22+ • Oxoanion has element surrounded by O atoms

  13. Polyatomic ions of the main group • -ate ending refers to ion with more O atoms (SO42-) • -ite refers to ion with fewer O atoms (SO32-) • In a group, charge on ion is the same • With more than two: • Per refers to ion with most O atoms (ClO4-) • Hypo refers to ion with least O atoms (ClO-)

  14. Other important polyatomic ions • Hydrogen carbonate or bicarbonate has H+ added • Cyanide is CN- • Acetate is CH3CO2- • Ammonium is NH4+

  15. The Name Game • Naming conventions are different for ionic and covalent compounds • Let’s play the name game to find out

  16. Distinguishing ion charge in the name • Follow rules of ionic compound names with one addition: • Identify ion charge by Roman numeral after metal name • Potential confusion caused by old names:–ic and –ous endings

  17. Molecular compounds • Don’t contain ions • Often have different compounds for the same elements

  18. Names and prefixes with molecular compounds • Distinguish in name by using prefixes • Used for every element in formula except when first one is single

  19. Acids • Acids are molecular compounds that produce H+ ions in solution HCl → H+(aq) + Cl-(aq) • H+ exists as H3O+ • Mineral acids: • HCl • HNO3 • H2SO4

  20. Carboxylic acids • Important class of acids in nature are carboxylic acids: • Acetic acid • Citric acid • Lactic acid • Malic acid • Formic acid • All contain -COOH

  21. Identifying acids: it can be confusing • Although all acids contain H • Not all compounds containing H are acids! • Mineral acids have H at beginning: • HNO3, HCl, H2SO4 • Not always with organic acids: • CH3COOH (also written HCH3COO

  22. Bases • Bases generate OH- in solution: NaOH→ Na+(aq) + OH-(aq) • Mineral bases contain OH- ions and metal ions • NaOH, Ba(OH)2 • Bases like NH3 react with H2O: NH3 + H2O → NH4+ + OH-

  23. Naming acids

  24. Acid and base strength • Strong acids and bases are completely ionized in H2O: • HCl, HNO3, NaOH, Ba(OH)2 • Weak acids and bases are partially ionized in H2O: • HNO2, CH3COOH, NH3

  25. Summary of naming

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