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Naming Chemical Compounds3221.3.1, 3221.3.2
Objectives
TLW write chemical formulas of ionic and molecular compounds.
TLW name chemical compounds using the correct system.
TLW use polyatomic ions.
Significance of a chemical formula• Recall that a chemical formula indicates the relative
number of atoms of each kind in a chemical formula
C8H18
• Hydrocarbon: molecular compounds composed only of hydrogen and carbon
Two Types of Chemical Compounds1. ionic: bond between anions (-) and cations (+)
(electrons are donated)nonmetal—metal
2. molecular: (covalently bonded—electrons are shared)
nonmetal—nonmetal3. Metallic: electron “sea” allowing few electrons to
be shared among many atomsmetal—metal
Monatomic Ions• Ions formed from a single atom• Groups 1 and 2 metals lose electrons to form cations• Groups 15, 16, and 17 gain electrons to form anions• Naming cations is very simple: identified by the
element’s nameK+ potassium cationMg2+ magnesium cation
• Naming anions: drop the ending to the element’s name and add –ium
O2- oxideCl- chloride
Transition metals have variable
charges!!!
Stock SystemWhen naming ionic compounds and an element has multiple possible charges, the charge is given in roman numerals in () after the name of the metal
Fe2+ iron (II)Fe3+ iron (III)
Naming a binary ionic compound according to the stock system illustrated below.
CuCl2
Binary Ionic Compounds• Binary compounds: compounds composed of two
elements• The total number of positives and negatives must
be equal, resulting in an overall neutral chargeNa Cl Mg Br2
Writing chemical formulas for binary ionic compounds
“crossing over”: a method of balancing charges between ions in an ionic compound
1. Write the symbols for the ions side by side. Write the cation (+) first!
2. Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion
3. Check to make sure the numbers are in the smallest possible ratio!
Naming Binary Ionic Compounds-The nomenclature, or naming system, of binary ionic compounds involves combining the names of the compound’s positive and negative ions-the cation is ALWAYS written first!!-charges are ONLY given as part of the name if multiple charges are possible
PracticePotassium and iodine
Magnesium and chlorine
Sodium and sulfur
Sulfur and aluminum
Nitrogen and aluminum
More practiceAgCl
ZnO
CaBr2
SrF2
BaO
CaCl2
Compounds containing polyatomic ions• Most polyatomic ions are oxyanions—polyatomic
ions that contain oxygen• Some elements can combine with oxygen to form
more than one type of oxyanionNO2
- nitrite (fewer O atoms) NO3- nitrate
SO32- sulfite (fewer O atoms) SO4
2- sulfate
Sometimes an atom can form more than 2 oxyanions…
Hypochlorite ClO- fewer O than –ite ionChlorite ClO2
-
Chlorate ClO3-
Perchlorate ClO4- one more O than –ate ion
Practice
Sodium iodide
Calcium chloride
Potassium sulfide
Lithium nitrate
Copper (II) sulfate
Sodium carbonate
Calcium nitrite
Potassium perchlorate
PracticeAgO
Ca(OH)2
KClO3
NH4OH
Fe2(CrO4)3
KClO
Naming Binary Molecular CompoundsUnlike ionic compounds, molecular compounds are composed of individually bonded units, or moleculesTwo Systems:1. Prefixes (“Old system”)2. Stock system (uses oxidation numbers)
NONMETAL—NONMETAL
ExamplesCCl4 carbon tetrachloride (tetra: prefix for 4)
CO2 carbon dioxide (di: prefix for 2)
P4O10 tetraphosphorus decoxide (deca: prefix for 10)
PrefixesNumber Prefix 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-
Binary Compounds of N and ON2O dinitrogen monoxide
NO nitrogen monoxideNO2 nitrogen dioxide
N2O3 dinitrogen trioxide
N2O4 dinitrogen tetraoxide
N2O5 dinitrogen pentoxide
No prefix is used for the first atom if it is a single atom
PracticeSO3
ICl3
PBr5
Carbon tetraiodide
Phosphorus trichloride
Dinitrogen trioxide