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Breakdown of Topics

Breakdown of Topics. Chemical formulas, Relation to Type of Substances, “Formula Unit” concept, and Visual connections (related to Tro, 3.3, 3.4) Ionic Compound Formulas Difference between ions and ionic compounds (formula writing) The “neutrality principle” concept

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Breakdown of Topics

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  1. Breakdown of Topics • Chemical formulas, Relation to Type of Substances, “Formula Unit” concept, and Visual connections (related to Tro, 3.3, 3.4) • Ionic Compound Formulas • Difference between ions and ionic compounds (formula writing) • The “neutrality principle” concept • Naming of Compounds (not elements!) • Ionic Compounds • Binary Molecular Compounds • Acids

  2. Sample B of NO2 Sample A of NO2 I. Chemical Formulas Revisited • Related to “nanoscopic pictures” • Every substance is composed of “basic units” • If sample A has “more of” a substance than sample B, it has more “basic units” of that substance: Jump to slide 11 • Every substance has a single chemical formula that represents its “basic unit” • One “unit” of any substance can be called a “formula unit”! (Here, one molecule = 1 formula unit)

  3. Monatomic Molecular Molecular Ionic Reminder …these do nothave a chemical formula Each of these has a chemical formula… Quick quiz: How many substances are in the box? Note: there are four kinds of substances… …and their formulas “tell you” which is which!... How many chemical formulas would be needed to describe the matter in the box? Ans. 2 (e.g., CS2 & O3)

  4. Fig. 3.4 Four types of substances—relationship to nanoscopic entities & chemical formulae Look closely at the different formulas—can tell the difference between an element and a compound? A monatomic vs polyatomic element?

  5. How do you recognize a monatomic element from a formula? • single element symbol with no subscript • Fe, Co, He One “unit” of the substance. The chemical formula represents one unit of a substance. Unit = atom Fe (s) He (g) Chemical formula State designation

  6. How do you recognize a molecular element from a formula? • A single element symbol with a subscript • S8, N2, P4, C60 One “unit” of the substance. The chemical formula represents one unit of a substance. Unit = molecule C60 (s) H2 (g) Chemical formula C60 Image: courtesy of J. Lauher's Fullerene Structure Library

  7. How do you recognize a molecular compound from a formula? • more than one element symbol ( compound) • first one is NOT that of a metallic element (exception later)( molecular) • CH4, SO2, SO3, P4O10 One “unit” of the substance. The chemical formula represents one unit of a substance. Unit = molecule CH4 (s) SO3 (g) Chemical formula

  8. How do you recognize an ionic compound from a formula? • more than one element symbol ( compound) • first one IS that of a metal (exception later) ( ionic) • NaCl, FeCl3, CuSO4, Na3PO4 The chemical formula still represents one unit of a substance, but it is not a separate grouping as in molecular substances. Basic units are “ions”… …but THE “unit” is a specific grouping of ions (indicated by the formula) NaCl (s) FeCl3 (s) …what do you call “it” (the “unit”)? Chemical formula …a “formula unit”!

  9. Formula units (FU) are the “basic units” of ionic compounds • A formula unit is an amount of a substance. You can have: • oneFU of NaClor • Two FU of NaClor • 25,333 FU of NaClor • 1.56 x 1021FU of NaCl Quick Quiz: Can you have: 4.3 FU of NaCl? 0.5 FU of CO2? NO! A FU is a “unit” of a substance—you cannot have a “fraction” of one! You can only have a whole number of them. • Just like you can have: • onemolecule of CO2or • Two molecules of CO2or • 25,333 molecules of CO2or • 1.56 x 1021molecules of CO2

  10. Formula Unit is just another term for “basic unit” of any substance • Most chemists use the term “formula unit” only with ionic compounds (b/c you can use “atom” or “molecule” for the other kinds of substances) • However, I often use the term with monatomic elements or molecular substances as well − e.g., 15 FU of CO2 means 15 molecules of CO2 − e.g., 432 FU of Fe means 432 atoms of Fe • “More” of a substance means more “formula units” of it!

  11. How many FUs of each substance are present? 7 6 8 5 ___ FU of Fe ___ FU of CH4 ___ FUof He ___ FU of SO3 To Slide 3 7 12 4 ___ FU of N2 ___ FU of NaCl ___ FU of FeCl3

  12. II. Ion and Ionic Compound Formulas • The chemical formula of any ion MUST show the charge as a superscript on the right: • Na+, Ru3+, Ca2+, O2-, NO2-, PO43- • Ions are not “compounds” (they’re not “substances”!) • The chemical formula of any ionic compound MUST show NO CHARGES AT ALL! • Na2O, Ru2O3, Ca(NO2)2, Na3PO4 NOTE: Your only clue that a formula of a compound represents an ionic compound is noticing the metal in front (exception later)

  13. Subscripts of ions tell you how many(of each) are in 1 FU Formula Na2O Ru2O3 Ca(NO2)2 Na3PO4 1 FU contains exactly: Two Na+ ions and one O2- ion Two Ru3+ ions and three O2- ions One Ca2+ ion and two NO2- ions Three Na+ ions and one PO43- ion NOTE: Parentheses are used ONLY if more than oneof a polyatomic ion is present in one FU.

  14. What determines the number of each ion in a formula unit of an ionic compound? • The charges on the cation and anion that make it up! • The oppositely charged ions will come together in the ratio that makes each formula unit electrically neutral • “neutrality principle”

  15. Neutrality Principle • A formula unit is always NEUTRAL overall The grouping of cations and anions must be neutral overall! • Total positive charge = total negative charge • Consistent with compound formula (no charge!) Formula Na2O: Na+ Na+ O2- +1 + (+1) + (-2) = 0 Na3PO4 Na+ Na+ Na+ PO43-  3(+1) + 1(-3) = 0

  16. Test: Use Neutrality Principle to Determine the Charge on an Ion Assume you know that O forms 2- ions (i.e. “O” = O2-) What is the charge on the Ru ions in Ru2O3? O2- 1 FU of compound; net charge must be zero Ru? O2- Ru? ANS: +3 3 x 2- = -6 for the three O2- ions. The two Ru ions must add up to +6 2 x ___ = +6 O2- +3 charge per ion

  17. Test: Use Neutrality Principle to Determine the Charge on an Ion What is the charge on the Pb ions in PbO2? 1 FU of compound; net charge must be zero O2- Pb? O2- ANS: +4 2 x 2- = -4 for the two O2- ions. The one Pb ion must add up to +4 **If you said +2 then you are using a shortcut instead of thinking about the MEANING of the subscripts! They are NOT “charges”—they represent the number of ions in 1 FU**

  18. Use the neutrality principle to determine the formula for an ionic compound Ions Fe3+ & Br- Ti4+ & S2- Ca2+ & PO43- NH4+ & SO42- Formula: FeBr3 TiS2 Ca3(PO4)2 The exception I mentioned earlier! (NH4)2SO4 Why do you need this skill? To determine the chemical formula from the name! “Cobalt(III) carbonate” is composed of cobalt(III) ions (Co3+) and carbonate ions (CO32-): Co2(CO3)3 Formula is: _________

  19. III.A Naming Ionic Compounds • Cation Name + Anion Name That’s it!!! • Hard part: names of the ions!

  20. Li+ Be2+ Mg2+ Na+ Al3+ Cations that always have the same charge (can memorize) Ca2+ Zn2+ K+ Ag+ Rb+ Sr2+ Cs+ Ba2+ 1) Monatomic, Type I cations (in this class) Ra2+ Fr+ • One Polyatomic cation (the “exception”): NH4+, ammonium ion

  21. Cations with more than one possible charge (Type II) need a Roman Numeral • Any metal cation other than those on previous slide! • Any transition metal ion other than Ag+ or Zn2+ • Any metal ion directly under the staircase other than Al3+ • Must use neutrality principle to figure out the charge (if not given to you)! • Write the chargeas a Roman numeral in parentheses

  22. Type II Cation Examples • Fe3+is iron(III) ion; Fe2+ is iron(II) • Pb4+ is lead(IV) ion; Pb2+ is lead(II) • Cu+ is copper(I) ion; Cu2+ is copper(II) • Cr6+is chromium(VI) ion; Cr3+ is chromium(III) • But: Ag+ is just silver ion (Type I) Zn2+ is just zinc ion (Type I)

  23. Anions—Preliminary Comment It will be much easier to learn anion names if you know these nonmetal elements’ symbols and names (next slide).

  24. Anions—Three Endings(-ide, -ate, and –ite) • -ides • Monatomic Use Periodic Table: P3- Phosphide • Two polyatomic ones to memorize CN- (cyanide); OH- (hydroxide)

  25. Anions (continued) • -ates • Polyatomic, contain oxygen (“oxoanions”) • Learn the four “core ions” first (next slide) • Then others from them…

  26. Some “–ate” ions to learn first… NO3- nitrate SO42- sulfate PO43- phosphate CO32- carbonate …and second (**Note that these are all analogous to nitrate**): ClO3- chlorate BrO3- bromate IO3- iodate

  27. Mnemonic-- “Poconoso” charge (negative) 3 2 1 2 POCONOSO # oxygen atoms 4 3 3 4 PO43- CO32- NO3- SO42-

  28. “Hydrogen ___” ions come from adding H+ to an oxoanion

  29. What’s the name of HS- ion? • Ans: hydrogen sulfide (not on sheet!)

  30. Anions (continued) • -ites • One fewer oxygen than “ate” counterpart • Sulfate → sulfite (SO42-→ SO32-)

  31. “-ites” come from “-ates”!

  32. “Per-” and “Hypo” in sets of four ClO4-perchlorate (from “hyper”, high) ClO3- chlorate ClO2- chlorite ClO- hypochlorite (from “hypo”, low) • Summary: Prefixes of “per” (4 O’s) and “hypo” (1 O) are added in cases where there are four “versions” instead of two.

  33. A few additional anions don’t follow any obvious pattern (memorize) • MnO4- permanganate (analogous to ClO4-) • C2H3O2- acetate • CrO42- chromate • Cr2O72- dichromate

  34. Examples!!! • See handout (and board for detailed solutions to Q’s below): • BaCO3 • Fe(NO3)2 • PbCl4 • AgClO barium carbonate iron(II) nitrate lead(IV) chloride silver hypochlorite Fe(OH)2 • iron(II) hydroxide _________________ • magnesium phosphite _____________ Mg3(PO3)2

  35. IIIB. Naming Binary Molecular Compounds • “binary”-two different kinds of atoms (2 different elements’ symbols in formula) • “molecular”- basic units are molecules • Molecules are made of atoms • Atoms are neutral • What’s the ratio of atoms in a molecule? • NO SINGLE “ANSWER” It varies! (no “neutrality” principle to “restrict” b/c atoms already neutral!) • CO and CO2; NO, N2O, NO2,, N2O4, etc. all exist! • Later, we’ll explore models of bonding…

  36. Naming Binary Molecular Compounds (continued) • Thus, prefixes are needed to let the reader know what that ratio (and exact composition of a FU) is! • Note: NO2 and N2O4 mean different things even though ratio is the same! • General “Recipe” for name: • 1st Element Name + 2nd element’s stem + -ide • Add prefixes as needed to the element or element stem • NOTE: “Mono” is left off 1st Element Name

  37. Examples • N2O: dinitrogen monoxide • NO2: nitrogen dioxide • NO: nitrogen monoxide • N2O4: dinitrogen tetroxide • P4O10: tetraphosphorus decoxide • CF4: carbon tetrafluoride • SCl6: sulfur hexachloride • http://www.youtube.com/watch?v=NJn76CR70oU (start at 3:20) • OR (better yet) Tro’s video [see Mastering practice]

  38. The Prefixes You Need to Know • 1: mono (only used on second element) • 2: di • 3: tri • 4: tetra • 5: penta • 6: hexa • 7: hepta • 8: octa • 9: nona • 10: deca

  39. Comment • Do not confuse the –ide ending with the “ides” of actual anions!!!!! • There are NO IONS in binary molecular compounds, even though the “ide” may make it sound as such! • CCl4, carbon tetrachloride does NOT contain any chloride ions. • I wish that the naming system were completely different for molecular compounds (no “–ides”), but I don’t get to decide!  • http://www.youtube.com/watch?v=NJn76CR70oU (start at 3:20)

  40. Examples SO3 • Sulfur trioxide __________________ • B2F6 __________________________ • SrF2 __________________________ diboron hexafluoride strontium fluoride (no “di” here!**) ** The last one is ionic, not molecular! Make sure to identify “ionic” vs. “molecular” before you begin to name a substance!!

  41. IIIC. Acids—A subset of molecular compounds • Molecular compounds that yield ions when dissolved in water!? (more later) • Always have H written first • Imagine making any acid by adding H+‘s to any anion in order to make a neutral formula unit. • The ENDING of the anion determines the name of the acid: • Ide → hydro ___ic acid • Ate → ____ic acid • Ite → ____ous acid • http://www.youtube.com/watch?v=a5nC2evhUa0 • http://www.youtube.com/watch?v=LoSLKUN7FQ4 (start at 1:35)

  42. Examples H2S • Hydrosulfuric acid _________________ • Sulfuric acid ______________________ • Chloric acid _______________________ • Hypochlorous acid _________________ • H3PO3 __________________________ • HNO3 ___________________________ • HNO2 ___________________________ • HCN ____________________________ H2SO4 HClO3 HClO phosphorous acid nitric acid nitrous acid hydrocyanic acid

  43. From Practice Handout *You don’t need to memorize oxalate

  44. For some web practice • http://www.stolaf.edu/depts/chemistry/courses/toolkits/125/js/naming/ • http://web.mst.edu/~gbert/names/Aionic.HTML • NOTE: This site does NOT do Type II metals at all!

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