Chemical Names and Formulas
Monatomic Ions
Cations
• Groups 1A, 2A, 3A charges = group number
• Name: element name “ion”
• Examples:
• Na+
• Mg2+
• Al3+
sodium ion
magnesium ion
aluminum ion
Common Cations
Monatomic Ions
Anions
• Group A element charges = 8 - group number
• Name: stem of element name + ide
• Examples
– Cl– S2– O2– N3-
chloride
sulfide
oxide
nitride
Monatomic Ions
Transition Metals (Group B)
• Charges can’t be predicted from Periodic Table
• Some are “multivalent”
– Form more than one ion
• Name: element name (charge) “ion”
• “Stock” naming system
– Use Roman numerals to indicate charge
•
•
•
•
•
Examples:
Fe2+
Fe3+
Cu+
Cu 2+
Stock name
iron (II) ion
iron (III) ion
copper (I) ion
copper (II) ion
Classical name
ferrous ion
ferric ion
cuprous ion
cupric ion
Ionic Charges of Representative
Elements
Multivalent Cations
Polyatomic Ions
• Group of covalently bonded atoms that has a
net charge
• Most are anions
• Oxyanions contain oxygen
– End in –ate or –ite
– SO42- sulfate
– NO3- nitrate
SO32- sulfite
NO2- nitrite
Common Anions
Chloroxyanions
• Polyatomic ions containing oxygen and
chlorine
Formula
Name
ClO-
hypochlorite
ClO2-
chlorite
ClO3-
chlorate
ClO4-
perchlorate
Polyatomic Ions
• Some begin with hydrogen
• H+ + CO32- → HCO3• H+ + PO43- → HPO42• H+ + HPO42- → H2PO4-
hydrogen carbonate
“bicarbonate”
hydrogen phosphate
“biphosphate”
dihydrogen phosphate
Polyatomic Cations
• Ammonium Ion
• H+ + :NH3 → NH4 +
NH4 +
9.3 Naming and Writing Formulas for Molecular
Compounds
• Molecular compounds are named using a system
of prefixes to indicate the number of each
element in the compound
• Do not use mono- before the first element
• Example: SF6 sulfur hexafluoride
• Example N2O4 dinitrogen tetroxide
9.4 Formulas and Names of Acids & Bases
• Acids are compounds that have one or more
ionizable hydrogens
• General formula HnX
• HCl (g) + H2O → H3O+ + Cl- (aq)
Common Acids
Names & Formulas for Bases
• Bases are compounds which produce the
hydroxide ion when dissolved in water
• NaOH (s) → Na+ (aq) + OH- (aq)
• NH3(g) + H2O → NH4+ (aq) + OH- (aq+
• Name as you would ionic compounds
Law of Definite Proportions
• aka Law of Constant Composition
• For any compound, the percent composition by
mass is always the same
• A given compound always contains elements in
exactly the same proportion by mass
• E.g. percent composition of water by mass is
11.1% H and 88.9% O regardless of how much or
how little there is
• An ice cube and an iceberg have the same %
composition.
Law of Multiple Proportions
• When two elements form different
compounds, the mass of one element
combining with the same mass of the other
element occur in small whole number ratios
H2O2
H2O
Mass O
32 g
16 g
Mass H
2g
2g
Ratio O:H
16:1
8:1
Ratio O:O
16:8 = 2:1
Flow Chart to Name Chemical
Compounds