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Chemical Formulae. symbols, naming, writing formulae. Symbols and Formulae. 118 known elements ten million known compounds elements - represented by chemical symbols (periodic table) compounds - represented by combos of chemical symbols so we need a very concise naming system!.

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Chemical Formulae


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chemical formulae
Chemical Formulae
  • symbols, naming, writing formulae
symbols and formulae
Symbols and Formulae
  • 118 known elements
  • ten million known compounds
    • elements - represented by chemical symbols (periodic table)
    • compounds - represented by combos of chemical symbols
  • so we need a very concise naming system!
some basics cations vs anions
Some basicscations vs anions
  • ions - electrically charged particle usually obtained from an atom by adding or removing electrons

anion - negatively charged particle

gains/adds electrons

cation - positively charged particle

loses/removes electrons

  • monatomicions - single atom with a charge
  • polyatomicions - several atoms covalently bonded but possessing an overall charge
monatomic naming cations
Monatomic NamingCations
  • You should remember or revisit monatomic naming handouts
  • cations are named by naming the element followed by the word “ion” (i.e. calcium ion)
  • specific charges can be found on the periodic table (see handout)
  • transition metals (gray boxes on handout) require Roman numerals because these elements have multiple oxidation numbers (charges): value of charge = oxidation number
monatomic naming cations1
Monatomic NamingCations
  • CAUTION
    • Silver ion is always 1+ and does not require a Roman numeral
    • Mercury (1) is Hg2+2 Mercury (II) Hg2+
    • Boron ion is B3+
    • Two polyatomic cations: ammonia (NH3+) and hydronium (H3O+)
monatomic naming anions
Monatomic NamingAnions
  • There are monatomic anions and polyatomic anions
  • Monatomic anions are named by naming the element, dropping the ending, and replacing with “-ide.” Charges can be determined from the periodic table (see handout).
monatomic naming anions1
Monatomic NamingAnions
  • CAUTION (monatomic anions)
    • nitrogen, hydrogen, oxygen, and phosphorus lose the last two syllables before adding “-ide”
    • oxide is O2- and peroxide is O22-
polyatomic anions
Polyatomic Anions
  • Polyatomic anions require a little work (see handout)
  • PLEASE learn the patterns for each group; they are clearly explained to you in the handout titled “Polyatomic Anions: The fifth level of the inferno”
  • If you know the “-ate” form of one member of each group you will be able to determine the other forms
polyatomic anions1
Polyatomic Anions
  • There are special cases of polyatomic ions that must be memorized, no trends! (see handout - 7th level)
    • acetate, cyanate, cyanide, hydroxide, oxalate, peroxide
polyatomic anions2
Polyatomic Anions
  • Sometimes there are prefixes with the polyatomic ions, this is memorization of prefix meanings
    • bi- and hydrogen: hydrogen ion (H+) is added and charge of polyatomic is changed
    • dihydrogen: two hydrogen ions are added and charge is changed
    • di-: two polyatomic ions bonded AND one oxygen atom is lost in the process (charge remains the same)
    • thio-: replace an oxygen with a sulfur
chemical symbols
Chemical Symbols
  • combo of symbols that represent the composition of the compound
  • indicates the elements present and the relative numbers of each element (subscripts)
oxidation numbers
Oxidation Numbers
  • predict oxidation number (charge on an atom) based on stability
  • to determine the ratio of elements in a compound when writing a chemical formula is to add charges algebraically to equal zero
ionic compounds
Ionic Compounds
  • compound/formula unit composed of cations and anions
  • positive ion is ALWAYS written first
  • gives the smallest possible integer number of different ions
  • parentheses enclose polyatomic ions when subscript is greater than one
  • ionic substances are electrically neutral
ionic compounds1
Ionic Compounds
  • Examples: Write the ionic compound that results from the combination of the following
      • calcium and bromine: Ca2+ and Br- : CaBr2
        • we need two bromines to balance the positive two charge of calcium
    • aluminum and sulfate: Al3+ and SO42-: Al2(SO4)3
        • we need two aluminums (@ 3+ each) to balance the three sulfates (@ 2- each)
ionic compounds2
Ionic Compounds
  • Shortcut: Cross-and-Drop Method
      • charge of cation becomes subscript of anion
      • charge of anion becomes subscript of cation
    • Examples: Write the ionic compound that results from the combination of the following
    • chromium and oxygen: Cr3+ and O2-
      • Cr3+ O2-: Cr2O3
ionic compounds3
Ionic Compounds
  • Naming ionic compounds: name of metal followed by anion name
    • Examples:
      • CaBr2 calcium bromide
      • CaCl2 calcium chloride
      • Al2(SO4)3 aluminum sulfate
      • Cr2O3 chromium oxide
      • SrO strontium oxide
try these
Try these...
  • Write the formula and name of the ionic compound that would result from the combination of the following ions
  • 1. K+ CrO42-
  • 2. Ca2+ O2-
  • 3. Pb4+ Cr2O72-
  • solutions:
    • 1. K2CrO4, potassium chromate
    • 2. CaO, calcium oxide
    • 3. Pb(Cr2O4)2, lead(IV) dichromate
try these1
Try these...
  • Write the ionic formula given the name of the compound
  • 1. iron(II) phosphate
  • 2. titanium (IV) oxalate
  • 3. thallium (III) nitrate
    • solutions:
      • 1. Fe3(PO4)2
      • 2. Ti(C2O4)2
      • 3. Tl(NO3)3
molecular compounds binary and organic
Molecular Compoundsbinary and organic
  • molecule - name given to covalently bonded compounds; formed by neutral elements combining
  • diatomic molecules - made of two atoms of the same element; there are 7 and they create a 7 on the periodic table (hydrogen does not help make the “7” due to placement)
  • H2, N2, O2, F2, Cl2, Br2, I2
binary molecular compounds
Binary Molecular Compounds
  • molecule composed of two elements; usually two nonmetals, two metalloids, or a nonmetal and metalloid
  • naming: use a prefix system
    • 1. name first element using exact element name
    • 2. name second element by writing stem of the name with the “-ide” ending
    • 3. add a Greek prefix to each element name to denote the subscript of each element in formula
      • (mono- is not usually used, unless needed to distinguish two compounds of the same two elements, CO2 and CO)
binary molecular compounds1
Binary Molecular Compounds
  • Greek prefixes
  • Oftentimes, the final vowel of prefix is dropped for ease in pronunciation (i.e. heptaoxide and heptoxide)
binary molecular compounds2
Binary Molecular Compounds
  • Examples:
    • N2O3: dinitrogen trioxide
    • P4O6: tetraphosphorus hexoxide
    • N2O4: dinotrogen tetroxide
    • SF6: sulfur hexafluoride
    • *note: the subscripts do not need to be the simplest ratio for molecular compounds
try these2
Try these…
  • Write the formula or name the following:
  • 1. Cl2O7
  • 2. disulfur trichloride
  • 3. SO3
  • 4. CO2
  • 5. carbon disulfide
  • 6. CO
  • solutions: 1. dichlorine hetpoxide; 2. S2Cl3; 3. sulfur trioxide; 4. carbon dioxide; 5. CS2; 6. carbon monoxide
organic molecular compounds usually called just organic compounds
Organic Molecular Compounds(usually called just organic compounds)
  • organic compounds - molecular substances that contain carbon combined with other elements (H, O, N…)
  • hydrocarbons - organic compounds that consist of only carbon and hydrogen (hence the name!)
organic compounds
Organic Compounds
  • naming hydrocarbons
  • 1. count the number of carbon atoms in the chain and select the appropriate stem (see next slide)
  • 2. add a suffix to indicate how the carbon atoms are attached (single, double, or triple bonds)
    • -ane (single bonds) CnH2n+2; n = number of carbon atoms, number of hydrogen atoms is 2n+2
    • -ene (double bond) CnH2n; n = number of carbon atoms, number of hydrogen atoms is 2n
    • -yne (triple bond) CnH2n-2; n = number of carbon atoms, number of hydrogen atoms is 2n-2
  • 3. combine prefix and suffix
organic compounds1
Organic Compounds
  • IUPAC Hydrocarbon Prefixes
organic compounds2
Organic Compounds
  • Example: name the following
  • C6H14
    • 1. C: 6 = hex
    • 2. H: 14 = 2n+2 = ane
    • 3. hexane
  • C3H6
    • 1. C: 3 = prop
    • 2. H: 6 = 2n = ene
    • 3. propene
organic compounds3
Organic Compounds
  • Examples: write the formula of the following
    • octyne: C8H14
    • methane: CH4(understood 1 for C)
try these3
Try these...
  • Write the name or formula for the following:
  • 1. C12H24
  • 2. nonane
  • 3. C20H42
  • 4. ethene
  • solutions: 1. dodecene; 2. C9H20; 3. icosane; 4. C2H4
please practice
Please Practice
  • There are several worksheets posted on moodle with solutions, please take some time to review naming concepts!
  • Please let me know of any difficulties or issues with this Keynote, PowerPoint, or PDF (whichever you select), thanks!