Chemical FormulaeChemical Formulaesymbols, naming, writing
formulae
Symbols and FormulaeSymbols 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 basicsSome basicscations vs anionscations 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
monatomic ions - single atom with a charge
polyatomic ions - several atoms covalently bonded but possessing an overall charge
Monatomic NamingMonatomic NamingCationsCations
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 NamingMonatomic NamingCationsCations
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 NamingMonatomic NamingAnionsAnions
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 NamingMonatomic NamingAnionsAnions
CAUTION (monatomic anions)
nitrogen, hydrogen, oxygen, and phosphorus lose the last two syllables before adding “-ide”
oxide is O2- and peroxide is O22-
Polyatomic AnionsPolyatomic AnionsPolyatomic 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 formsSuffix General number of oxygen atoms
per- whatever -ate 1 more oxygen than “-ate”
whatever -ate usually the most common form
whatever -ite 1 less oxygen than “-ate”
hypo- whatever -ite 1 less oxygen than “-ite”
Polyatomic AnionsPolyatomic 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 AnionsPolyatomic 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 SymbolsChemical Symbols
combo of symbols that represent the composition of the compound
indicates the elements present and the relative numbers of each element (subscripts)
Oxidation NumbersOxidation 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 CompoundsIonic Compoundscompound/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 CompoundsIonic 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 CompoundsIonic CompoundsShortcut: 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 CompoundsIonic CompoundsNaming 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 these...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 CompoundsMolecular Compoundsbinary and organicbinary 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 Binary Molecular CompoundsCompoundsmolecule 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 Binary Molecular CompoundsCompounds
Greek prefixes
Oftentimes, the final vowel of prefix is dropped for ease in pronunciation (i.e. heptaoxide and heptoxide)
subscript prefix
1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
6 hexa-
7 hepta-
8 octa-
9 nona-
10 deca-
Binary Molecular Binary Molecular CompoundsCompounds
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 these…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 Organic Molecular CompoundsCompounds (usually called just organic (usually called just organic
compounds)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 CompoundsOrganic Compoundsnaming 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 CompoundsOrganic Compounds
IUPAC Hydrocarbon Prefixes
# of carbon atoms prefix
1 meth-
2 eth-
3 prop-
4 but-
5 pent-
6 hex-
7 hept-
8 oct-
9 non-
10 dec-
11 undec-
12 dodec-
20 iscos-
Organic CompoundsOrganic CompoundsExample: 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 CompoundsOrganic Compounds
Examples: write the formula of the following
octyne: C8H14
methane: CH4 (understood 1 for C)
Try these...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 PracticePlease 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!
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