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!