naming and formula writing. chemical formulas molecular: indicates the numbers of each atom in a...

Naming and Formula Writing

Chemical Formulas

• molecular: indicates the numbers of each atom in a compound

C6H12O6

notation with numbers & symbols to show composition of a compound

• empirical: gives simplest whole-number ratio of atoms of elements

CH2O

• structural: indicates how the atoms are bonded to each other

Molecules• monatomic: single atoms of the same

elementEx: He, Ne, Kr, Xe, Rn (noble gases)

(the 1 subscript is understood)• diatomic: two atoms of the same element

Ex: H2, O2, N2, Br2

• more than two atoms of the same elementEx: P4 & S8

• two or more atoms of different elementsEx: H2O, NH4, CO2

Charges on all the atoms that make up a compound must add up to zero

Crisscross method for writing the formulas of binary ionic compounds

• the charge of each ion becomes the subscript for the other ion

(without + / - signs)• use simplest whole-number subscripts

Ex: calcium bromide Ca+2 + Br-1 CaBr2

• *same with polyatomic ions, but put

polyatomic ion in parentheses

Ex: calcium hydroxide Ca+2 + OH-1 Ca(OH)2

Some ions can exist with different charges (Fe+2 or Fe+3)

• remember that charges must = zero

• look at name to figure out charge

Ex: iron II chloride Fe? + Cl-1 FeCl2

Practice

• Strontium oxide calcium sulfide• Potassium carbonate lead (II) sulfate• Magnesium sulfide copper (I) chlorate• Strontium nitrate dihydrogen monosulfide• phosphorus pentachloride calcium

chloride• Sodium sulfide rubidium sulfide• Iron (III) chlorate

Rules for Naming Compounds

Basic Rule:

1) Name the first element in the compound

2) Name the second element by changing the ending of the name to –ide

OR if the compound is made up of more than 2 elements, you have a polyatomic ion and you will use the polyatomic ion’s name with no changes

Naming a Metal and a Nonmetal

• Basic rule—no changes

Ex: NaCl sodium chloride

CaSO4 calcium sulfate

Naming Compounds with transition metals

• Basic rule with one change:– Find the charge of the transition metal

(the charge of a transition metal can change)– Write the charge after the transition metal’s

name (in Roman numerals)

Ex CoI2 cobalt (II) iodide

Fe(ClO3) 3 iron (III) chlorate

Naming 2 nonmetals• Basic rule with one change:

– Look at the number of atoms for the second nonmetal and select the correct prefix to add to the name:Prefix Meaning

mono- 1

di- 2

tri- 3

tetra- 4

penta- 5

hexa- 6

2 nonmetals (continued):Ex CO carbon monoxide

CO2 carbon dioxide• If the 1st element in the compound has more

than one atom, a prefix must be added to the first element’s name also

2nd elment always gets a prefix,1st element only gets a prefix if more than one atom

Ex P2S3 diphosphorus trisulfide

N2O5 dinitrogen pentoxide• Usually you won’t have 2 vowels together

– Exceptions: di-, tri-, tetra-, & penta- iodide and oxide

Practice• CaS NiCl

• MgCl2 SiCl4• Zn(NO3)2 K2CO3

• Hg(C2H3O2)3 Li2SO4

• LiBr PCl5• H2O PbSO4

• SrO CF4

• Ag(CrO4) 2 CS2