Ionic Compounds: Writing Formulas and Names Formula Units.
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Transcript of Ionic Compounds: Writing Formulas and Names Formula Units.
Ionic Compounds:Writing Formulas and Names
Formula Units
Empirical FormulasEmpirical Formulas
• Give the smallest whole-number ratio of elements in the compound.
• Ionic compounds have empirical formulas only.
Identify the empirical formulas
• H2O• H2O2
• CaF2
• NaCl• CH4
• C2H6
• NiO• FeCl3
Empirical and possibly MolecularEmpirical and possibly Molecular
MolecularMolecular
Empirical and IonicEmpirical and Ionic
Empirical and IonicEmpirical and Ionic
Empirical and possibly MolecularEmpirical and possibly Molecular
MolecularMolecular
Empirical and Ionic
Empirical and Ionic
Formula Unit
• The simplest ratio of the ions in an ionic compound.
• KBr means potassium ions and bromide ions are in a 1-to-1 ratio and is the formula unit.
• For ionic compounds, the formula mass is based on the formula unit.
Binary CompoundsBinary Compounds
• Composed of two elements–Positive monatomic metal ion
–Negative monatomic nonmetal ion
–Monoatomic ion is a one-atom ion.
Note: A binary compound may contain more than 2 ions but only 2 kinds of ions like Al2O3.
Oxidation Number or StateOxidation Number or State
• Charge of a monatomic ion.
• Given by right superscript.
• Some elements form only 1 ion.
• Some elements can form more than 1 ion.
• Try to find patterns.
Ca+2
Na+1
OO-2-2
FeFe+2+2 and Fe and Fe+3+3
Oxidation State of Selected Oxidation State of Selected ElementsElements
• Group 1 ions always +1• Group 2 ions always +2• MOST group 13 ions are +3• Groups 14, 15, 16, and 17 have multiple
oxidation states, both positive and negative. (Start with the first ox #)
• Transition metals (Group B) can have more than 1 oxidation state but always positive.
Writing Formulas for Binary Cmpds
• The first rule in writing formulas for ionic compounds is
POSITIVE ION FIRSTPOSITIVE ION FIRST
But how do you get the subscripts?But how do you get the subscripts?
We will start by writing formulas from the ions.
Writing Formulas for Binary Cmpds
• Compounds are electrically neutral – no charge.
• Take the number of each kind of ion X the charge on the ion. Sum these terms. Should get 0.
• Positive and negative charges must balance out.
Equal but Opposite Charges
• Na+1 and Cl-1: NaCl +1 + (-1) = 0
• Mg+2 and O-2: MgO +2 + (-2) = 0
• Al+3 and P-3: AlP +3 + (-3) = 0
• Rule: Just write the symbols, POSITIVE FIRSTPOSITIVE FIRST!
Try a few formulas:
• Li+1 and I-1
• Ca+2 and O-2
• Al+3 and N-3
• K+1 and F-1
• Ba+2 and S-2
LiILiICaOCaO
AlNAlN
KFKF
BaSBaS
Criss-Cross Method
• When the charges don’t cancel out immediately:
• Mg+2 and Cl-1, CROSS and DROP!CROSS and DROP!• (Numbers only, forget signs!)(Numbers only, forget signs!)
• Mg1Cl2 but if the subscript is 1, forget it!
• MgCl2 means 1 Mg+2 and 2 Cl-1
Check the Math
• MgCl2 means 1 Mg+2 and 2 Cl-1
• (1 X +2) + (2 X -1) = 2 – 2 = 0
• The charges add up to zero!
Try a few formulas:
• Ca+2 + Cl-1
• Na+1 + O-2
• Cs+1 + S-2
• Al+3 + Cl-1
• Al+3 + Se-2
• Mg+2 + F-1
• K+1 + N-3
CaClCaCl22NaNa22OO
CsCs22SSAlClAlCl33AlAl22SeSe33
MgFMgF22
KK33NN
Of course, it gets more difficult
• Potassium (K) and Fluorine (F)• Zinc (Zn) and Iodine (I)• Sodium (Na) and Oxygen (O)• Magnesium (Mg) and Oxygen (O)• Aluminum (Al) and Oxygen (O)• Calcium (Ca) and Bromine (Br)• Cesium (Cs) and Iodine (I)• Silver (Ag) and Sulfur (S)
KFKF
NaNa22OO
MgOMgOAlAl22OO33
CaBrCaBr22
CsICsI
ZnIZnI22
AgAg22SS
Naming Binary Ionic Compounds
1. Always name the metal (the cation or positive ion) first and use its full name.
2. Write the stemstem of the nonmetal (the anion or negative ion).
3. Add the ending “ide” to the nonmetal.
Stems of nonmetals
Nitr Ox Fluor
Phosph Sulf Chlor
Arsen Selen Brom
Tellur Iod
Hydr is the stem for H
The First Step in NamingThe First Step in Naming
• Look up the positive metal in the periodic table in your reference tables.
• If the metal has only one oxidation state (possible charge), it’s easy.
• If the metal has more than one oxidation state, there’s an extra step.
Metals with one oxidation state
• CaO• BaS• AlN• LiCl• Al2Se3
• Na2O• K3N• MgF2
Calcium OxideCalcium OxideBarium SulfideBarium SulfideAluminum NitrideAluminum Nitride
Lithium ChlorideLithium ChlorideAluminum SelenideAluminum Selenide
Sodium OxideSodium OxidePotassium NitridePotassium NitrideMagnesium FluorideMagnesium Fluoride
Metals with > 1 oxidation state.
• Use the formula to figure out which Use the formula to figure out which oxidation state the metal ion has.oxidation state the metal ion has.
• Ex: Fe can be Fe+2 oror Fe+3
• Name FeO and Fe2O3. These are
two differenttwo different compounds. You cannot name them iron oxide. Every formula goes with 1 name and vice-versa.
FeO and Fe2O3
• Compounds are electrically neutral.
• Oxygen is -2.
FeOFeO
Name:Name:Iron (II) oxideIron (II) oxideThe roman numeral II is The roman numeral II is the charge on the Fe.the charge on the Fe.
1 O which is -2.1 O which is -2.The Fe must be +2.The Fe must be +2.
FeO and Fe2O3
• Compounds are electrically neutral.
• Oxygen is -2.
FeFe22OO33
Each O is -2.Each O is -2.
There are 3 O’s.There are 3 O’s.3 X (-2) = -6.3 X (-2) = -6.Total negative charge.Total negative charge.
Total positive Total positive charge must charge must be +6.be +6.
Each Fe is +3.Each Fe is +3.Iron (III) oxideIron (III) oxide
Name the followingHint: Positive Always FirstPositive Always First
• TiCl3• Mn2O4
• Co2O3
• PdBr2
• AuCl3• MoN• MnO• TiO
Titanium (III) chlorideTitanium (III) chloride
Manganese (IV) oxideManganese (IV) oxide
Cobalt (III) oxideCobalt (III) oxide
Palladium (II) bromidePalladium (II) bromideGold (III) chlorideGold (III) chloride
Molybdenum (III) nitrideMolybdenum (III) nitride
Manganese (II) oxideManganese (II) oxide
Titanium (II) oxideTitanium (II) oxide
POLYATOMIC IONSPOLYATOMIC IONS
• A group of covalently bonded atoms that carries a charge.
• See Table E. May be +’ve or –’ve.
• Polyatomic ions have “names.”
• Because they are charged, polyatomic ions can form ionic bonds with oppositely-charged ions.
SOSO442-2- CO CO33
2-2- PO PO443-3- OH OH--
Ternary (or more) Compounds
• Contain 3 or more elements (uppercase letters)
• Usually have a polyatomic ion– If the polyatomic is +’ ve, it’s bonded to a
nonmetal– If the polyatomic is –’ve, it’s bonded to a
metal– Once in a while, 2 polyatomics are
bonded together.
Formulas with polyatomicsFormulas with polyatomics
• What’s the formula for the compound formed from NH4
+1 and Cl-1?
• The charges add up to zero, so just write the symbols, positive first!
NHNH44ClCl
Try a few more:
• Na+ and OH-
• K + and HCO3-1
• Mg+2 and CO3-2
• Li + and NO3-
• NH4 + and CN-
• Ca+2 and SO4-2
NaOHNaOH
KHCOKHCO33
MgCOMgCO33
LiNOLiNO33
NHNH44CNCN
CaSOCaSO44
These are more challenging:
• Mg+2 and (PO4)-3
• (NH4)+1 and S-2
• Al+3 and (NO3)-1
• Fe+2 and OH-1
• Hg2+2 and SCN-1
• Mg+2 and HCO3-
• Al+3 and C2O42-
MgMg33(PO(PO44))22
(NH(NH44))22SS
Al(NOAl(NO33))33
Fe(OH)Fe(OH)22
HgHg22(SCN)(SCN)22
Mg(HCOMg(HCO33))22
AlAl22(C(C22OO44))33
Some of the most challenging are
• Zinc + Nitrate ion• Magnesium + Hydroxide ion• Lithium + Carbonate ion• Ammonium ion + Bromine• Potassium + Sulfate ion• Calcium + Phosphate ion• Beryllium + Chlorate ion• Ammonium ion + Sulfate ion
Zn(NOZn(NO33))22
Mg(OH)Mg(OH)22
LiLi22COCO33
NHNH44BrBrKK22SOSO44
CaCa33(PO(PO44))22
Be(ClOBe(ClO33))22
(NH(NH44))22SOSO44
Naming compounds with polyatomics
• Polyatomic ions have names, given in Table E.
• Naming is parallel to binary naming.
• Positive always first.
• If +’ve ion is a metal, check to see how many oxidation states it has. If > 1, name has a roman numeral.
• If –’ve is polyatomic, 2nd part of name is name of polyatomic. Don’t modify ending.
Name the following
• NaOHNaOH• KHCOKHCO33
• LiNOLiNO33
• CaSOCaSO44
• Al(NOAl(NO33))33
• Fe(OH)Fe(OH)22
• CuSOCuSO44
• CuSCNCuSCN
Sodium hydroxideSodium hydroxidePotassium hydrogen carbonatePotassium hydrogen carbonate
Lithium nitrateLithium nitrateCalcium sulfateCalcium sulfate
Aluminum nitrateAluminum nitrateIron (II) hydroxideIron (II) hydroxide
Copper (II) sulfateCopper (II) sulfateCopper (I) thiocyanateCopper (I) thiocyanate
Summary for Ionic CompoundsSummary for Ionic Compounds
• Name = metal + stem of nonmetal + ide.
• If the metal has more than 1 oxidation state, it has a roman numeral in the name.
• Formula: positive first, always.
• Compounds are electrically neutral.
• Use oxidation states you know, like O, to figure out the oxidation states that have more than 1 possibility.