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Molecules

Molecules. Most elements found in nature are not found as isolated atoms. Noble gases are common exceptions. Most natural materials are composed of either: molecules Ions Molecules and ions are both formed from atoms. Molecules. Molecule:

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Molecules

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  1. Molecules • Most elements found in nature are not found as isolated atoms. • Noble gases are common exceptions. • Most natural materials are composed of either: • molecules • Ions • Molecules and ions are both formed from atoms.

  2. Molecules • Molecule: • A group of atoms combined in definite proportions and held together by strong attractive forces calledcovalent chemical bonds • Covalent bonds are formed when two atoms share two or more electrons • The smallest representative particle of a molecular compound

  3. Molecular Compounds • Molecular compounds • composed of molecules that contain more than one type of atom • Examples: • Water (H2O) • Ethyl alcohol (C2H6O) • Carbon dioxide (CO2) • Ozone (O3) • Most molecular substances are composed of non-metals only.

  4. Chemical Formulas • Chemical Formula • notation that describes the types and relative numbers of atoms in a pure substance • Chemical formulas always contain: • elemental symbols • subscripts • show the relative number of each type of atom

  5. Chemical Formulas • Molecular Formulas • chemical formulas that tell theactual numberof each type of atom in a molecule • provide the greatest information about a compound Acetic Acid C2H4O2 Glucose C6H12O6

  6. Chemical Formulas • Empirical Formula • chemical formula that tells the smallest whole number ratio of each type of atom in a molecule • NO2 vs. N2O4 • HO vs. H2O2 • CH2 vs. C3H6

  7. Ions and Ionic Compounds • Some compounds are composed of ions instead of molecules. • “Salt” (NaCl) • contains Na+ and Cl- ions • Tums (CaCO3) • Contains Ca2+ and CO32- ions • Milk of Magnesia [Mg(OH)2] • Contains Mg2+ and OH-

  8. Ions and Ionic Compounds • Ions form when atoms (or groups of atoms) gain or lose electrons • Ions can be either • monoatomic • polyatomic • Monoatomic ion: • a charged substance containing a single atom that has gained or lost electrons

  9. Predicting Ionic Charge • Many atoms gain or lose electrons in such a way that they end up with the same number of electrons as the nearest (closest in atomic number) noble gas. • “octet” rule Ca (20p, 20e-) Ca2+ (20p, 18e-) [Ar: 18p,18e-] O (8p, 8e-) O2- (8p, 10e-) [Ne: 10p, 10e-]

  10. Predicting Ionic Charge • Using the octet rule you can easily determine the charge on most of the monoatomic ions formed by the main group elements. • Main group metal cations: • Charge = group number • Main group nonmetal anions: • Charge = group # - 8 (or simply count the number of “spaces” away from the nearest noble gas and add a negative sign)

  11. Ions and Ionic Compounds Common monoatomic ions P3- Zn2+ Ag+ • In general: • Metal atoms lose e- and form cations. • Nonmetal atoms gain e- and form anions.

  12. Cr2+ Cr3+ Mn2+ Mn3+ Fe2+ Fe3+ Co2+ Co3+ Cu+ Cu2+ Sn2+ Sn4+ Pb2+ Pb4+ Bi3+ Bi5+ Ions and Ionic Compounds Many transition metals and a few main group elements form more than one ion. Main group Main group

  13. Ions and Ionic Compounds • Polyatomic ion: • an electrically charged group of two or more atoms that are held together by covalent bonds • Polyatomic ions cannot be broken into smaller pieces • Examples: • NO3- • SO42- • HCO3- • PO43-

  14. Polyatomic Ions • Some common polyatomic ions: • Ammonium NH4+ • Hydroxide OH- • Cyanide CN- • Nitrate NO3- • Acetate C2H3O2- • Sulfate SO42- • Bisulfate (Hydrogen sulfate) HSO4- • Carbonate CO32- • Bicarbonate (Hydrogen carbonate) HCO3- • Phosphate PO43-

  15. Common Ions • You are responsible for naming and writing formulas for compounds containing the ions shown in the Ion Chart given to you at the start of the semester. • You should be able to write the names and formulas for binary molecular compounds and the common acids shown in this set of notes. • You should also know the formulas and names of compounds that you use in the laboratory.

  16. Ionic Compounds • Ionic Compound • a compound that contains both cations (+ charge) and anions (- charge) • Ionic compounds generally contain a metal and one or more nonmetals. • Molecular compounds generally contain nonmetals only.

  17. Structures & Formulas of Ionic Compounds • The ions in an ionic compound are arranged in a 3-D structure. • There are no discrete molecules of an ionic compound. • Ionic compounds are represented using empirical formulas

  18. Na+ Na+ Cl- Formulas of Ionic Compounds • Ionic compounds must be electrically neutral. • Total positive charge = total negative charge Na+ + Cl- NaCl (1 pos, 1 neg)

  19. Cl- Cl- Ca2+ Ca2+ Ca2+ + 2Cl- CaCl2(2 pos, 2 neg) Cl- Formulas of Ionic Compounds Ca2+ + Cl- CaCl (2 pos, 1 neg)

  20. Formulas of Ionic Compounds • To write the empirical formula for an ionic compound: • Determine the charge on each ion. • Combine the ions in a ratio that gives electrically neutral compound • If charges on the ions are equal in magnitude (but opposite in sign), then combine the ions in a 1:1 ratio.

  21. Na+ F- Ca2+ Ca2++ SO42- CaSO4 SO42- Formulas of Ionic Compounds Na+ + F-NaF

  22. Formulas of Ionic Compounds • If charges on the ions are different, then the charge of one ion becomes the subscript of the other ion. Mg+2 Cl -1 Mg1Cl2 MgCl2 • If the subscripts are not the lowest whole number ratio, divide them by the greatest common factor.

  23. O2- O2- O2- Al3+ Al3+ Formulas of Ionic Compounds Example: Write the correct formula for a compound containing Al3+ and O2- ions Al2O3 Al3+O 2-

  24. SO42- SO42- SO42- Al3+ Al3+ Formulas of Ionic Compounds Example: Write the empirical formula for the compound formed from Al3+ and SO42- ions. Al2(SO4)3 Al3+ SO42-

  25. Formulas of Ionic Compounds Example: What are the empirical formulas for the compounds formed from: • Ca2+ and N3- • Sn4+ and SO42- Remember to use ( ) around polyatomic ions if you need more than one of them.

  26. Names & Formulas of Ionic Compounds • Ionic compounds are named using the names of the ions that compose them. • You must know the names and charges of all ions, including the polyatomic ions. • Ion chart hand-out • Trends discussed during lecture • General format for naming ionic compounds: • Cation name followed by anion name

  27. Naming Cations • Cations formed from metal ions have the same name as the metal. K+ potassium ion Ca2+ calcium ion Al3+ aluminum ion

  28. Naming Cations • Many transition metals and a few main group metals can form more than one cation (i.e. two or more charges) • the charge of the specific cation is given by Roman numeral in parentheses after the name of the metal Fe2+ iron (II) ion Fe3+ iron (III) ion Cu+ copper (I) ion Cu2+ copper (II) ion

  29. Naming Cations • Two common polyatomic cations NH4+ ammonium ion H3O+ hydronium ion

  30. Naming Anions • Monoatomic anions • drop the ending of the element’s name • add “ide” N nitrogen N3- nitride O oxygen O2- oxide

  31. Naming Anions • Some simple polyatomic anions also use the “ide” ending OH- hydroxide CN- cyanide O22- peroxide

  32. Naming Oxyanions • Oxyanions(polyatomic anions containing oxygen) have names ending in: • “ate” most common oxyanion of the element • “ite” same charge, 1 less O NO3- nitrateSO42- sulfate NO2-nitriteSO32-sulfite

  33. Oxyanions (cont.) • Prefixes are added if more than 2 oxyanions exist: • “per” 1 more O than the “ate” oxyanion • “hypo” 1 less O than the “ite” oxyanion ClO4-perchlorate ClO3- chlorate ClO2- chlorite ClO-hypochlorite

  34. Oxyanions • To learn & remember the names and formulas of the oxyanions: • learn the name and formula for the “ate” oxyanion • apply the rules discussed previously

  35. Oxyanions • The names & formulas of the common oxyanions can be learned using trends within the same group of elements: • Halogens: • The “ate” anion has 3 oxygens and a 1- charge • ClO3- = chlorate ion • BrO3- = bromate ion

  36. Oxyanions • Group 6 (S, Se, Te): • The “ate” anion has 4 oxygens and a 2- charge • SO42- = sulfate • SeO42- = selenate • Group 5 (N, P, As): • The “ate” anion has 4 oxygens and a 3- charge except for Nitrogen • PO43- = phosphate • NO3- = nitrate

  37. Oxyanions • Other common oxyanions that you must know: • MnO4- = permanganate ion • CrO42- = chromate ion • Cr2O72- = dichromate ion

  38. Oxyanions • Anions derived by adding H+ to an oxyanion: • add “hydrogen” or “dihydrogen” as prefix to oxyanion name CO32-carbonate HCO3-hydrogen carbonate(also called bicarbonate) PO43-phosphate H2 PO4- dihydrogenphosphate

  39. Ionic Compounds • Ionic compounds are named by: • Cation name followed by anion name NaCl CaBr2 NaClO Cu(NO3)2 sodium chloride calcium bromide sodium hypochlorite copper (II) nitrate

  40. Examples Example: Write the names of these ionic compounds. • Na2O • FeCl3 • (NH4)3PO4 • KClO4 • Pb(CO3)2

  41. Writing Formulas from Names • To write the correct empirical formula from the name of an ionic compound: • Identify the symbol and charge for each ion. • Determine the correct number of each ion needed to balance the charges.

  42. Writing Formulas from Names Example: Write the empirical formula for ammonium sulfate ammonium sulfate NH4+ (NH4)2SO4 SO42-

  43. Writing Formulas from Names Example: Write the formulas for these ionic compounds • sodium bicarbonate • barium nitrate • sodium bromate • iron(III) carbonate • sodium hydrogen phosphate • potassium dichromate • tin (IV) oxide

  44. Names & Formulas of Acids • Acid:a substance whose molecules form H+ ions when dissolved in water • HCl (aq) • HCN (g) • HClO3 (aq) • Name of acid depends on the type of acid, its physical state, and the name of the anion.

  45. Names & Formulas of Acids • Three naming systems for acids: • Acids containing oxygen • Acids without oxygen • aqueous solutions • gases

  46. Naming Acids • To name an acid: • Does it have oxygen? • Yes • Write name of anion • Change “ate” to “ic acid” • Example: HClO4 = perchloric acid • Change “ite” to “ous acid” • Example: HClO2 = chlorous acid

  47. Naming Acids • To name an acid: • If no oxygen, is it (aq)? • Yes • Start with hydro • Add the name of anion • Change “ide” to “ic acid” • Example: HCl (aq) = hydrochloric acid

  48. Naming Acids • To name an acid: • If no oxygen, is it (g)? • Yes • Start with hydrogen • Add the name of the anion • Example: HCN (g) = hydrogen cyanide

  49. Naming Acids • You must know the names and formulas for the following acids for the exam: • HCl (aq) hydrochloric acid • HBr (aq) hydrobromic acid • HI (aq) hydroiodic acid • HNO3 nitric acid • HClO4 perchloric acid • HClO3 chloric acid • H2SO4 sulfuric acid

  50. Naming Acids • You must know the names and formulas for the following acids for the exam: • HF (aq) hydrofluoric acid • H2S (g) hydrogen sulfide • HCN (g) hydrogen cyanide • HC2H3O2 acetic acid • H2CO3 carbonic acid • H3PO4 phosphoric acid

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