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2011-09-30 18:28:37

ch.5 Molecules & Compounds
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  1. What happens when two elements are combined?

    *Compounds are composed of atoms in fixed ratios.
    Their properties completely change.

    • Ex: Sodium: poisonous
    • Chlorine: poisonous

    = Sodium Chloride: table salt (safe)
  2. Who is Joseph Proust, and state his law.
    Law of constant composition:

    All samples of a given compund have the sam eproportions of their constituent elements.

    (the composition of each compound is constant)
  3. Diagram of the mass ratio for the decompositino of water.
    18.0 g sample of water:

    Mass ratio = 16.0 g O (oxygen) / 2.0 g H (hydrogen)

    = 8.0, or 8.0:1.
  4. Diagram of the water element.

    H: symbol for hydrogen.

    2: Subscript indicating 2 hydrogen atoms.

    O: Symbol for oxygen.

    *Implied subscript of 1 indicating 1 "oxygen" atom
  5. Characteristic of subscripts.
    The subscripts in a chemical formula represent the relative numbers of each type of atom in a chemical formula.
  6. What is the general rule for the ordering of elements?

    Ex: CO2? Not O2C
    Elements on the left are generally listed before elements on the right.

    The more metal-like element is listed first (elements to the left; Metals).

    For columns, elements toward the bottom are more metal-like than elements toward the top.
  7. Diagram for Mg(NO3)2.

    Defining total # of subscripts.

    Mg: symbol for magnesium

    *Implied subscript indicating 1 Mg atom.

    *(after N) Impled subscript indicating 1 nitrogen atom per NO3- group.

    3: subscript indicating 3 oxygen atoms per NO3- group

    2: subscript indicating 2, NO3-, groups.


    Mg: 1 Mg

    N: 1 x 2 = 2 N (implied 1 inside parentheses times 2 outside parentheses)

    O: 3 x 2 = 6 O (3 insdide parantheses times 2 outside parentheses).
  8. What are the 3 types of chemical formulas?

    Define them.
    1) Empirical: gives the simplest whole-number ratio of atoms of each element in a compound

    Ex: Hydrogen Peroxide: H2O2 (emp. is HO)

    2) Molecular: gives the actual number of atoms of each element in a molecule of the compound.

    *3-d representation of models.

    Ex: H2O2 (hydrogen peroxide)

    3) Structural: uses lines to represent chemical bonds and shows how the atoms in a molecule are connected to each other.

    Ex: Hydrogen Peroxide is H-O-O-H.
  9. Pure Substances are either elements/compounds (ch.3),
    Elements may either be what two compositions?

    Compounds may either be what to comositions?
    Elements: atomic (Ne); Molecular (O2)

    Compounds: Molecular (H2O); Ionic (NaCl)
  10. Define (molecular element) diatomic molecules.

    *Since molecular elements do not usually exist in nature w/ single atoms as their basic units, they must exist as diatomic molecules.
    Two atoms of that element bonded together-as their basic units.

    Ex: Hydrogen-H2 molecules; Oxygen-O2 molecules; chlorine-Cl2 molecules.
  11. What are the elements that occur as diatomic molecules?
    H2, N2, O2, F2, Cl2, Br2, I2

    (hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, iodine)
  12. Define Ionic compound

    Define Molecular compound

    Define atomic element
    ionic compound: Contain one or more cations paired w/ one or more anions, the cations are metals and the anions are nonmetals.

    KNO3 (metal + 2 nonmetals)

    molecular compound: Compounds formed from two or more nonmetals (2+ nonmetals)

    Ex: H2O (water); CO2 molecules (dry ice)

    Atomic elements: those that exist in nature w/ single atoms as their basic units.

    Molecular elements: do not normally exist in nature w/ single atoms as their basic units. They exist as diatomic molecules.
  13. What is the difference between a cation and an anion?
    cation is a positively charged atom or group of atoms.

    anion is a negatively charged atom or group of atoms.
  14. Writing formulas for ionic compounds.
    In general:

    1) Ionic compounds always contain positive & negative ions.

    2) In the chemical formula, the sum of the charges of positive ions (cations) must always equal the sum of the charges of the negative ions (anions).
  15. Naming Ionic Compounds (5.7)

    Ionic compounds are categorized into what two types?
    1) Meta forms only one type of ion.

    2) Metal forms more than one type of ion.
  16. Naming binary ionic compounds containing a metal that forms only one type of cation.
    Name of cation (metal); base name of anion (nonmetal) + -ide.

    Ex: NaCl

    Consists of the cation, sodium, followed by the base name of the anion, chlor, with the ending, -ide. Full name: sodium chloride.
  17. Naming binary ionc compounds containing a metal that forms more than one type of cation.

    The full name for these types of compounds have the form:
    Name of cation (metal)-->

    (charge of cation (metal) in roman numerals in parentheses)) -->

    • base name of anion (nonmetal) + -ide.
    • Ex: FeCl3 = iron(III) chloride (iron is the cation followed by the charge of the cation in parentheses (III), followed by the anion chlor, with the ending -ide.

    Full name: iron(III) oxide

    • *The charge of iron must be 3+ in order for the compound to be charge neutral.

  18. (5.9, pg. 140) Naming ionic compounds containing a metal that forms more than one type of cation.

    *Name the compound: PbCl4
    Pb = cation lead, followed by the charge of the cation in parentheses (IV), followed by the base name of anion, chlor-, with the ending -ide.

    Full name: lead(IV) chloride.

    The charge on Pb is 4+ because the charge on Cl is 1-. Since there are 4 Cl- anions, the Pb cation must be Pb4+.
  19. Naming ionic compounds containing a polyatomic ion.

    Ex: KNO3 = potassium nitrate

    If there are more than 2 ions in the series, then the prefixes hypo-, meaning "less than," and per-, meaning "more than," are used


    ClO- is called perchlorate, meaning "more oxygen than chlorate"

    • ClO- hypochlorite
    • ClO2- chlorite
    • ClO3- chlorate
    • ClO4- perchlorate
  20. Naming Molecular Compounds

    Ex: CO2 = carbon dioxide

    ~CCl4, BCl3
    [prefix][name of 1st element]

    [prefix][name of 2nd element + -ide]

    When writing the name of a molecular compound, as when writing the formula, the 1st is the more metal-like one.

    The prefixes given to each element indicate the # of atoms present.

    • ~CCl4 = carbon tetrachloride
    • ~BCl3 = boron trichloride
  21. Translate the following to the correct # of atoms in these prefixes.

    1, 2, 3, 4, 5, 6, 7, 8, 9, 10
    • 1-mono
    • 2-di
    • 3-tri
    • 4-tetra
    • 5-penta
    • 6-hexa
    • 7-hepta
    • 8-octa
    • 9-nona
    • 10-deca
  22. Define acids.
    molecular compounds that produce H+ ions when dissolved in water.

    *They're composed of H and one or more nonmetals in their formula.
  23. Acids can be seperated into what two groups?

    (model below)
    binary acids: those containing only hydrogen and only a nonmetal.

    oxyacids: those containing hydrogen, a nonmetal, and oxygen.

    • Binary:
    • contains only 2 elements

    • Oxyacids:
    • contain oxygen

    ***All depends on the # of elements in the acid.
  24. Naming binary acids:

    hydro+base name of nonmetal + -ic + acid

    Ex: define HCl(aq), HBr(aq)
    hydrochlor -ic acid

    hydrobrom -ic acid
  25. Naming oxyacids.

    -ite: name of oxyanion ends in -ite =ous

    -ate: name of oxyanion ends in -ate =ic

    The names of acids containing oxyanions ending with -ate takes this form:

    [base name of oxyanion + -ic] + [acid]

    Ex: H2SO3(aq) = sulfurous acid

    Ex(2): HNO3(aq) = nitric acid
  26. Nomenclature Summary:

    Name the steps in order to identify and name the different categories of compounds in this chapter.
    1) Decide whether the compound is ionic, molecular, or an acid.

    2) You can recognizer ionic compounds by the presence of a metal + a nonmetal.

    Molecular compounds by two or more nonmetals only,

    and acids by the presence of hydrogen (written first) and one or more nonmetals.
  27. define the formula mass.
    Formula mass =

    (# of atoms of 1st element in chemical formula x atomic mass of 1st element)

    + (plus)

    (# of atoms of 2nd element in chemical formula x atomic mass of 2nd element)

    Ex: CCl4

    • = 1 x (atomic mass C) + 4 x (atomic mass Cl)
    • =12.01 amu + 4(35.45 amu)
    • =12.01 amu + 141.80 amu
    • =153.8 amu (one decimal pt. addition rule of sfs)