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Unit 6B: Naming and Writing Formulas for Ionic and Covalent Compounds
Polyatomic Ions
Polyatomic ions are groups of atoms that are covalently bonded and have a charge.• PO4
3- = phosphate ion
• SO42- = sulfate ion
Polyatomic Ions
Ending of –ate or –ite means there are oxygen atoms in the formula of the ion. • SO4
2- = sulfate
• SO32- = sulfite
Polyatomic Ions
The –ate ending always has one more oxygen than the –ite ending.
SO42- = sulfate NO3
- = nitrate
SO32- = sulfite NO2
- = nitrite
Names for Cations and Anions
Monatomic Cation Names: Same as element name• Na+ sodium ion• Al3+ aluminum ion
Names for Cations and Anions
What about transition metals with more than one charge? • Fe2+ iron(II)• Fe3+ iron(III)
Names for Cations and Anions
What about transition metals with more than one charge?• Cu+ copper(I)• Cu2+ copper(II)
Names for Cations and Anions
Monatomic Anion Names: Element name with –ide ending• S2- sulfide ion• O2- oxide ion
Names for Cations and Anions
Monatomic Anion Names: Element name with –ide ending• P3- phosphide ion• N3- nitride ion
Naming Binary Ionic Compounds
A binary compound is composed of two elements and can be ionic or molecular (covalent).• Binary ionic compound = metal, then
nonmetal
Naming Binary Ionic Compounds
NaCl • sodium chlorideCa3P2 • calcium phosphide
CuCl2 • copper(II) chlorideNi3N2 • nickel(II) nitride
Naming Compounds with Polyatomic Ions
To name an ionic compound with a polyatomic ion, write the name of the cation first, followed by the name of the anion.
Naming Compounds with Polyatomic Ions
NaNO3 • sodium nitrate(NH4)2SO4 • ammonium sulfate
Ca(NO3)2 • calcium nitrate
Writing Formulas for Ionic Compounds
The metal (cation) always goes first, followed by the nonmetal (anion).
Writing Formulas for Ionic Compounds
Use the “criss-cross method” to balance out the charges.
Writing Formulas for Ionic Compounds
Use the “criss-cross method” to balance out the charges.
Parenthesis must be used if more than one polyatomic ion is needed.
Writing Formulas for Ionic Compounds
Use the “criss-cross method” to balance out the charges.
Always reduce the subscripts to lowest terms
Naming Binary Molecular Compounds
We use prefixes to tell how many of each element are in a binary molecular compound.
Naming Binary Molecular Compounds
Name the elements in the order listed in the compound, using prefixes to indicate the number of each element.• Never use the prefix mono- for the first
element• The second element always ends in -ide
Naming Binary Molecular Compounds
CO• carbon monoxideCO2
• carbon dioxide
P4O10
• tetraphosphorus decoxide
N2O5
• dinitrogen pentoxide
Writing Formulas forBinary Molecular Compounds
Write the formula in the same order the elements are named.
The prefix tells you the subscript for each element.
Writing Formulas forBinary Molecular Compounds
Dioxygen monofluoride • O2F
Phosphorus trichloride• PCl3
Review
Binary Ionic Compounds Binary Molecular Compounds
Electrons Give and Take Shared
Type of Elements Metal + Nonmetal Nonmetal + Nonmetal
Naming NO prefixes YES prefixes
YES Roman numerals (if > 1 charge) NO Roman numerals
Review
