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Naming and Formula Writing for Ionic and Covalent Compounds
Naming and Formula Writing for Ionic and Covalent Compounds
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Objectives… List differences among ionic and
covalently bonded compounds Identify polyatomic and monatomic
ions and name them properly Write the chemical formulas and
names for ionic compounds Write the chemical names and
formulas of acids Write the chemical names and
formulas of molecules
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Review of Ionic Compounds (Crystals)
Transfer of electrons Made from a metal and a non-metal Metals lose electrons, nonmetals gain
electrons Chemical formula is arranged in the
smallest whole number ratio (empirical formula) Formula unit: the smallest repeating pattern
within a crystal
Even though ionic compounds are made up of ions, they ARE ELECTRICALLY NEUTRAL!
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Ions can be monatomic or polyatomic: Monatomic: Made up of a single atom Polyatomic: Made up of multiple atoms
Remember…Group #: 1 2 13 14 15 16 17 18Charge: +1 +2 +3 X -3 -2 -1 X
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Monatomic cations have the same name as the element Example: Na+1 = Sodium ion, Ca+2 =
Calcium ion
Monatomic anions have the ending of the element name changed to“-ide” Example: Cl-1=chloride ion, O-
2=oxide ion
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Polyatomic ions: (See polyatomic ion sheet) are
made up of two or more elements
covalently bonded together with an overall
positive or negative charge.
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Review Molecular Compounds (Molecules)
Sharing of electrons Made from nonmetals only Molecules of the same compound are
IDENTICAL and INDEPENDENT of each other
Chemical formula indicates the exact makeup of one molecule (molecular formula)
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Rules for Formula Writing (Ionic Compounds)
Since all compounds are neutral, figure out how many of each ion is needed to make a neutral compound. (Neutral means having a net zero charge.)
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Examples
Mg and ClMg+2 Cl-1
Cl-1
Al and OAl+3 O-2
Al+3 O-2
O-2
MgCl2
Al2O3
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More Examples
Ca and SCa+2 S-2
Ca and (AsO4)
Ca+2 (AsO4)-3
Ca+2 (AsO4)-3
Ca+2
CaS
Ca3(AsO4)2
Parentheses are needed if there is more than one of the polyatomic ions!
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Aluminum SulfiteAl+3 (SO3)-2
Al+3 (SO3)-2
(SO3)-2
Chemical Name to Formula
Al2(SO3)3
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More Examples
Silver SulfateAg? (SO4)-2
Ag+1
Ag2(SO4)Ag+1
Use your Periodic Table to determine the charge
on transition metals!
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More Examples
Nickel (II) NitrateNi+2 (NO3)-1
(NO3)-1 Ni(NO3)2
The Roman Numeral will always tell you the charge and it will always be positive
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More Examples
Iron (III) ChlorideFe+3 Cl-1
Cl-1
Cl-1FeCl3
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Chemical Formula to NameRecall the format for chemical formulas…
(name of cation – metal) (name of anion – nonmetal)
Examples:KBr
CaI2
Na(SO4)
Potassium Bromide
Calcium Iodide
Sodium Sulfate
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For elements with more than one possible charge (transition metals)
…Use the charge on the anion to determine the charge on the
cation!Example:
Fe2(CrO4)3
-2(3)=-6+6/2=+3
Iron (III) Chromate
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Example:Sn(CO3)2
-2(2)=-4+4
Tin (IV) Carbonate
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Example:Cu3P
-3+3/3=+1
Copper (I) Phosphide
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Criss Cross Short Hand MethodJust use the number of the charge (not the charge itself) and criss cross as shown
below. You will note that the overall charge is neutral, as the total positive charge of the metals offsets the total negative charge of the nonmetal.
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Naming Acids
Acids are ionic compounds that contain H+1 as their cation.
Acids are named based on their anion.
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If the anion ends in…
“-ide” hydro ___ ic acid
Example: H2S
Hydrosulfuric acid
Sulfide (S-2) is the anion!
The root name of the anion goes here
(remove-ide)
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If the anion ends in…
“-ate” ___ ic acid
Example: H2SO4
Sulfuric acid
Sulfate (SO4-2) is the
anion!
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If the anion ends in…
“-ite” ___ ous acid
Example: H2SO3
Sulfurous acid
Sulfite (SO3-2) is the anion!
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Mnemonic devices to help you remember Acid Nomenclatire
#1) “eight is great”er number of oxygens
“ite” is slight” less number of oxygens
#2) Chemistry “Diseases” (joke..I am suffering from eight-ic-ite-ous or)....
“ate” -ic “ite”-ous
SO4 = sulfate SO3 = sulfite
H2SO4 H2SO3
Sulfuric Acid Sulfurous Acid
or
lessous icmore
NO2 = nitrite NO3 = nitrate
HNO2 nitrous acid HNO3 nitric acid
PO3 = phosphite PO4 = phosphate
H3PO3= phoshporous Acid H3PO4 = phosphoric Acid
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Formula Writing
Use the reverse to determine the anion and balance out the
charges for a neutral compound.
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Examples
Hydrophosphoric acid
H+1 P-3
H+1
H+1
All acids contain a H+1 charge as the cation!
Ask yourself, “What was the original
ending?”H3P
Original ending “ide”
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Examples
Chromic acid
H+1 (CrO4)-2
H+1
Original ending “ate”
H2CrO4
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Naming Molecular Compounds
Recall, covalently bonded molecules are made up of
nonmetals only.
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Prefixes
mono – 1 hexa – 6di – 2 hepta – 7tri – 3 octa – 8tetra – 4 nona –
9penta – 5 deca -
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Must be memorized!
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RulesUse the prefixes to indicate how many of each element is in one molecule.Change the ending on the second element to “-ide”
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ExamplesN2O4
CO
SiO2
If there is only one of the first element, do not write mono.
dinitrogen tetraoxide
carbon monoxide
silicon dioxide
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Formula WritingUse the prefixes to determine the subscripts
Examples: trisulfur hexafluoride
carbon pentaoxide
tetraphosphrous dioxide
S3F6
DO NOT REDUCE!
CO5
P4O2