chapter 7 chemical formulas & chemical compounds
DESCRIPTION
Chapter 7 Chemical Formulas & Chemical Compounds. 7.1 Chemical Names & Formulas. Ions. Cation : A positive ion Mg 2+ , NH 4 + Anion : A negative ion Cl - , SO 4 2 - Ionic Bonding : Force of attraction between oppositely charged ions. Predicting Ionic Charges. Groups 3 - 12 :. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 7Chapter 7Chemical Formulas &Chemical Formulas &Chemical CompoundsChemical Compounds
7.1 Chemical Names & Formulas
IonsIons• Cation: A positive ion
• Mg2+, NH4+
• Anion: A negative ion
• Cl, SO42
• Ionic Bonding: Force of attraction between oppositely charged ions.
Predicting Ionic ChargesGroups 3 - 12Groups 3 - 12:: Many Many transitiontransition elements have elements have
more than one possible more than one possible oxidation state.oxidation state.
Iron (II) = Fe2+
Iron (III) = Fe3+
Predicting Ionic ChargesGroups 3 - 12Groups 3 - 12:: Some Some transitiontransition elements elements
have only one possible have only one possible oxidation state.oxidation state.
Zinc = Zn2+
Silver = Ag1+
Formula Writing for Binary Ionic Compounds
Magnesium Bromide
Mg+ 2 Br – 1
Mg1Br2
MgBr2
Calcium Sulfide
Ca + 2 S – 2
Ca2S2
CaS
criss-cross the oxidation numbers to balance criss-cross the oxidation numbers to balance out the charge.out the charge.
Writing Ionic Compound FormulasExample: Iron (III) chloride
1. Write the formulas for the cation and anion, including CHARGES!
FeFe3+3+ ClCl--2. Check to see if charges are balanced.
3. Balance charges, if necessary, using subscripts.
Not balanced!
33
Naming Ionic CompoundsNaming Ionic Compounds
1. Cation first, then anion
2. Monatomic cation = name of the element
• Ca2+ = calcium ion
3. Monatomic anion = root + -ide• Cl = chloride
• CaCl2 = calcium chloride
Naming Ionic CompoundsNaming Ionic Compounds
• some metal forms more than one cation
• use Roman numeral in name
• PbCl2
• Pb2+ is cation
• PbCl2 = lead (II) chloride
Metals with multiple oxidation statesMetals with multiple oxidation states
Elements with Multiple Oxidation Numbers
Copper ICopper I Cu Cu+1+1
Copper IICopper II Cu Cu+2+2
Iron IIIron II Fe Fe+2+2
Iron IIIIron III Fe Fe+3+3
Mercury IMercury I Hg Hg+1+1
Mercury IIMercury II Hg Hg+2+2
Lead IILead II Pb Pb+2+2
Lead IVLead IV Pb Pb+4+4
Tin IITin II Sn Sn+2+2
Tin IVTin IV Sn Sn+4+4
Chromium IIChromium II Cr Cr+2+2
Chromium III CrChromium III Cr+3+3
Chromium VI CrChromium VI Cr+6+6
Manganese IIManganese II MnMn+2+2
Manganese IIIManganese III MnMn+3+3
Manganese VIIManganese VII MnMn+7+7
Cobalt IICobalt II CoCo+2+2
Cobalt IIICobalt III CoCo+3+3
Gold IGold I AuAu+1+1
Gold IIIGold III AuAu+3+3
Nickel IINickel II NiNi+2+2
Nickel IIINickel III NiNi+3+3
Nickel IVNickel IV NiNi+4+4
**Silver**Silver Ag Ag+1+1
**Zinc**Zinc Zn Zn+2+2
**Cadmium Cd**Cadmium Cd+2+2
♥ Poly Atomic Ions to Know and Love ♥ Name Formula Name Formula
AcetateAcetateCC22HH33OO22
-1-1
(CH(CH33COO COO -1-1))
HypochloriteHypochlorite ClOClO-1-1
DichromateDichromate CrCr22OO77
-2-2 ChloriteChlorite ClOClO22
-1-1
AmmoniumAmmonium NHNH44
+1+1 ChlorateChlorate ClOClO33
-1-1
NitrateNitrate NONO33
-1-1 PerchloratePerchlorate ClOClO44
-1-1
NitriteNitrite NONO22
-1-1 CyanideCyanide CNCN-1-1
HydroxideHydroxide OHOH-1-1 CarbonateCarbonate COCO33
-2-2
PhosphatePhosphate POPO44
-3-3 ChromateChromate CrOCrO44
-2-2
SulfiteSulfite SOSO33
-2-2 Hydrogen Hydrogen CarbonateCarbonate
HCOHCO33
-1-1
SulfateSulfate SOSO44
-2-2 Hydrogen Hydrogen PhosphatePhosphate
HPOHPO44
-2-2
Hydrogen Hydrogen SulfiteSulfite
HSOHSO33
-1-1 Hydrogen Hydrogen SulfateSulfate
HSOHSO44
-1-1
PermanganatePermanganate MnOMnO44
-1-1 OxalateOxalate CC22OO44-2-2
HydroniumHydronium HH33OO++ SilicateSilicate SiOSiO
33-2-2
PeroxidePeroxide OO22-2-2 PhosphitePhosphite POPO
33-3-3
BromateBromate BrOBrO33
-1-1 ArsenateArsenate AsOAsO44
-2-2
♥ More Poly Atomic Ions to Know and Love ♥
Name Formula Name Formula
Naming Compounds with Polyatomic Ions
Formula Name
• (NH4)2SO4 ammonium sulfate
• ZnCO3 zinc carbonate
• NH4Br ammonium bromide
• Li2CO3 lithium carbonate
* Polyatomic & monatomic cation names remain the same, monatomic anions change their ending to –ide.
Writing Ionic Compound Formulas
Example: Barium nitrate
1. Write the formulas for the cation and anion, including CHARGES!
BaBa2+2+ NONO33--
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
( )( )22
Writing Ionic Compound Formulas
Example: Ammonium sulfate
1. Write the formulas for the cation and anion, including CHARGES!
NHNH44++ SOSO44
2-2-
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
( )( )22
Writing Ionic Compound Formulas
Example: Aluminum sulfide
1. Write the formulas for the cation and anion, including CHARGES!
AlAl3+3+ SS2-2-
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
22 33
Writing Ionic Compound Formulas
Example: Magnesium carbonate
1. Write the formulas for the cation and anion, including CHARGES!
MgMg2+2+ COCO332-2-
2. Check to see if charges are balanced.
They are balanced!
3. Simplify to a formula unit.
Writing Ionic Compound Formulas
Example: Zinc hydroxide
1. Write the formulas for the cation and anion, including CHARGES!
ZnZn2+2+ OHOH--
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
( )( ) 22
Writing Ionic Compound Formulas
Example: Aluminum phosphate
1. Write the formulas for the cation and anion, including CHARGES!
AlAl3+3+ POPO443-3-
2. Check to see if charges are balanced.
They ARE balanced!
More Examples…
1. Cr2O3 2. Cr2O 3. CuSO4
4. Ni(OH)2
5. Cr2(C2O4)3
6. Cu2S7. CuS
1. chromium (III) oxide2. chromium (I) oxide3. copper (II) sulfate4. nickel (II) hydroxide5. chromium (III) oxalate6. copper (I) sulfide7. copper (II) sulfide
Chemical Formula Chemical Name
Hydrates• Hydrate – when a water molecule (s) are
chemically bonded to the ionic compound.
• Normal ionic naming protocol are used, then followed by the word “hydrate.”
• Prefixes are added to indicate the number of water molecules when naming hydrates.
Hydrate Prefixes
# of water molecules
prefix # of water molecules
prefix
1 mono- 6 hexa-
2 di- 7 hepta-
3 tri- 8 octa-
4 tetra- 9 nona-
5 penta- 10 deca-
Hydrates• Example: MgBr2 ∙ 6H2O
Magnesium bromide hexahydrate
• The “ ∙ ” means “loosely bonded”
• Hygroscopic - easily absorb water molecules from the air.
• Deliquescent- very hygroscopic; takes out water from the air to dissolve completely to form a liquid solution.
• Anhydrous – when all of the water has been removed.
Naming Binary Covalent CompoundsNaming Binary Covalent Compounds• Compounds between two nonmetals• First element in the formula is named first.• Second element is named as if it were an anion.• Use prefixes• Only use mono on second element
PP22OO55 = =COCO22 = =CO =CO =
NN22O =O =
didiphosphorus phosphorus pentpentoxideoxidecarbon carbon didioxideoxidecarbon carbon monmonoxideoxidedidinitrogen nitrogen monmonoxideoxide
Acids• Acids always begin with Hydrogen
Anion Formula Name
Cl-1 HCl Hydrochloric Acid
Br-1 HBr Hydrobromic Acid
SO4-2 H2SO4 Sulfuric Acid
SO3-2 H2SO3 Sulfurous Acid
NO3-1 HNO3 Nitric Acid
CN-1 HCN Hydrocyanic Acid
PO4-3 H3PO4 Phosphoric Acid
Bases
Cation Formula Name
Na+1 NaOH Sodium Hydroxide
K+1 KOH Potassium Hydroxide
NH4+1 NH3 Ammonia
Organic Compounds
• Organic compounds are named using a different set of rules.
• The simplest group is the hydrocarbons. These compounds are composed solely of the elements carbon and hydrogen.
• Carbon atoms can link to each other in chains and in rings.
Naming Hydrocarbons• The stem of the compound name is then
chosen from the following table:
# of carbon atoms
prefix # of carbon atoms
prefix
1 meth- 6 hexa-
2 eth- 7 hepta-
3 prop- 8 octa-
4 but- 9 nona-
5 penta- 10 deca-
Hydrocarbons: Alkanes
• These molecules have the generic formula: CnH2n+2
• They contain all single bonds.
CH4 methane
C2H6 ethane
C3H8 propane
C4H10 butane
C5H12 pentane
C6H14 hexane
Hydrocarbons: Alkenes
• These molecules have the generic formula:
CnH2n
• They contain double bonds between carbon atoms.
C2H4 ethene
C3H6 propene
C4H8 butene
C5H10 pentene
C6H12 hexene
Hydrocarbons: Alkynes
• These molecules have the generic formula:
CnHn
• They contain triple bonds between carbon atoms.
C2H2 ethyne
C3H3 propyne
C4H4 butyne
C5H5 pentyne
C6H6 hexyne
Chapter 7Chapter 7Chemical Formulas &Chemical Formulas &Chemical CompoundsChemical Compounds
7.2 Oxidation Numbers
Oxidation Numbers
• Oxidation Number – numbers assigned to atoms composing a compound or ion that indicate the general distribution of electrons among bonded atoms
Chapter 7Chapter 7Chemical Formulas &Chemical Formulas &Chemical CompoundsChemical Compounds
7.3 Using Chemical Formulas
Molar Mass• The mass of 1 mole of a pure substance is called
its Molar Mass.
• Ex: Molar mass of Iron is 55.847 g/mol
What is the molar mass of Platinum?
195.08 g/mol
Molar Mass• The molar mass depends on the particles that
compose the compound. If your element exists as a molecule, i.e. BrINClHOF, one mole of these particles contains 2 moles of the element as an atom.
• Determine the molar mass of oxygen molecules (O2)
(16.00 g/mol) x (2 atoms) = 32.00 g/mol
The molar mass of oxygen molecules (O2) is twice the molar mass of oxygen atoms!
Formula Mass
• The molar mass of a compound is the mass of the atomic mass units of one molecule.
• This takes into consideration the number of atoms of each element in a compound.
• Formula Mass is calculated the same way as molar mass except it is measured in amu, instead of g/mol.
Calculating Formula Mass
Calculate the formula mass of magnesium carbonate, MgCOCalculate the formula mass of magnesium carbonate, MgCO33..
24.31 + 12.01 + 3(16.00) =24.31 + 12.01 + 3(16.00) = 84.32 amu84.32 amu
Steps for Calculating Molar Mass for Compounds
1. List the elements
2. Determine how many atoms of each
3. Identify the atomic masses from the periodic table
4. Multiply how many atoms by the respective atomic mass
5. Add up the totals for the Molar Mass
Practice• H2O
H 2 x 1.008 = 2.016
O 1 x 15.99 = 15.99
18.006
• C6H12O6
C 6 x 12.01 = 72.06
H 12 x 1.008 = 12.096
O 6 x 15.99 = 95.94
180.096
• NaCl
Na 1 x 22.9 = 22.9
Cl 1 x 35.45 = 35.45
58.35
• K2O
K 2 x 39.1 = 78.2
O 1 x 15.99 = 15.99
94.19
g/mol
g/mol
g/molg/mol
Calculating Percentage Composition
Calculate the percentage composition of magnesium Calculate the percentage composition of magnesium carbonate, MgCOcarbonate, MgCO33..
24.31 + 12.01 + 3(16.00) = 84.32 amu24.31 + 12.01 + 3(16.00) = 84.32 amu
24.31100 28.83%
84.32Mg
12.01
100 14.24%84.32
C 48.00
100 56.93%84.32
O
100.00
• So…. In one mole of H2O, how many grams of Hydrogen are there?
2 mol H x 1.008g H = 2.016 g H in 1 mol H2O 1 mol H
• What % of Hydrogen, by mass, is in H2O?
2.016 g H x 100 = 11.2 % H 18 g H20
*Must also find molar mass of H2O
What % of Oxygen, by mass is in H2O?
Mass Percent
Formulas
molecular formula = (empirical formula)n
[n = integer] molecular formula = C6H6 = (CH)6
empirical formula = CH
Empirical formula: the lowest whole number ratio of atoms in a compound.
Molecular formula: the true number of atoms of each element in the formula of a compound.
Formulas
Formulas for Formulas for ionic compoundsionic compounds are are ALWAYSALWAYS empirical (lowest whole number ratio). Often, empirical (lowest whole number ratio). Often, these are called these are called formula unitsformula units..
Examples:Examples:
NaCl MgCl2 Al2(SO4)3 K2CO3
Formulas
Formulas for Formulas for molecular compoundsmolecular compounds MIGHTMIGHT be be empirical (lowest whole number ratio).empirical (lowest whole number ratio).
Molecular:Molecular:
H2O
C6H12O6 C12H22O11
Empirical:
H2O
CH2O C12H22O11
Chapter 7Chapter 7Chemical Formulas &Chemical Formulas &Chemical CompoundsChemical Compounds
7.4 Determining Chemical Formulas
Empirical Formula Determination
1. Base calculation on assumption of 100 grams of compound.
2. Determine moles of each element in 100 grams of compound.
3. Divide each value of moles by the smallest of the values.
4. Multiply each number by an integer to obtain all whole numbers.
Empirical Formula DeterminationAdipic acid contains 49.32% C, 43.84% O, and 6.85% H by mass. What is the empirical formula of adipic acid?
49.32 14.107
12.01
g C mol Cmol C
g C
6.85 16.78
1.01
g H mol Hmol H
g H
43.84 12.74
16.00
g O mol Omol O
g O
Empirical Formula Determination(part 2)
4.1071.50
2.74
mol C
mol O
6.782.47
2.74
mol H
mol O
2.741.00
2.74
mol O
mol O
Divide each value of moles by the smallest of the values.Divide each value of moles by the smallest of the values.
Carbon:Carbon:
Hydrogen:Hydrogen:
Oxygen:Oxygen:
Empirical Formula Determination(part 3)
Multiply each number by an integer to obtain all whole Multiply each number by an integer to obtain all whole numbers.numbers.
Carbon: 1.50Carbon: 1.50 Hydrogen: 2.50Hydrogen: 2.50 Oxygen: 1.00Oxygen: 1.00x 2 x 2 x 2
33 55 22
Empirical formula: C3H5O2
Finding the Molecular FormulaThe empirical formula for adipic acid is The empirical formula for adipic acid is CC33HH55OO22. The molecular mass of adipic acid is . The molecular mass of adipic acid is
146 g/mol. What is the molecular formula of 146 g/mol. What is the molecular formula of adipic acid?adipic acid?
1. Find the formula mass of C1. Find the formula mass of C33HH55OO22
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
Finding the Molecular FormulaThe empirical formula for adipic acid is The empirical formula for adipic acid is CC33HH55OO22. The molecular mass of adipic acid is . The molecular mass of adipic acid is
146 g/mol. What is the molecular formula of 146 g/mol. What is the molecular formula of adipic acid?adipic acid?
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
2. Divide the molecular mass by the 2. Divide the molecular mass by the mass given by the emipirical formula.mass given by the emipirical formula.
1462
73
Finding the Molecular FormulaThe empirical formula for adipic acid is The empirical formula for adipic acid is CC33HH55OO22. The molecular mass of adipic acid is . The molecular mass of adipic acid is
146 g/mol. What is the molecular formula of 146 g/mol. What is the molecular formula of adipic acid?adipic acid?
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
1462
73
3. Multiply the empirical formula by this 3. Multiply the empirical formula by this number to get the molecular formula.number to get the molecular formula.
(C(C33HH55OO22) x 2 =) x 2 = CC66HH1010OO44
Determining Chemical Formulas from Mass Percents
A sample has been analyzed, here are the results:
18.8 % Na
29.0 % Cl
52.2 % O
• How can you determine the chemical formula?
• Step 1: Assume a 100 g sample.
Then, your percent quantities become gram (mass) quantities.
18.8 g Na , 29.0 g Cl & 52.2 g O• Step 2: Convert those masses to moles.
18.8 g Na x 1 mol Na = 0.817 mol Na
23 g Na
29.0 g Cl x 1 mol Cl = 0.817 mol Cl
35.5 g Cl
52.2 g O x 1 mol O = 3.26 mol O
16 g O
• Step 3: Since your empirical formula is in small, whole number ratios, divide your mole amounts by the smallest mole quantity.
0.817 mol Na / 0.817 = 1.00 mol Na
0.817 mol Cl / 0.817 = 1.00 mol Cl
3.26 mol O / 0.817 = 3.99 ≈ 4.00 mol O
• Step 4: Use these values as subscripts in your formula
Na1Cl1O4 ≈ NaClO4
• Step 5: In the event the chemical formula is not the same as the empirical formula, you need the molar mass of the desired compound and you must compare it to the molar mass of the empirical formula.
• Step 6: Divide the given molar mass by the empirical molar mass to get the multiple quantity.
• Step 7: Multiply each subscript in the formula by that multiple quantity.
• Ex: MM of molecular formula = 180 g/mol
Using steps 1-4, you found that the empirical formula is CH2O.
Find the molar mass of the empirical formula: MM EF = 30 g/mol
Divide MM MF / MM EF to get a whole number.
Ex: 180 / 30 = 6
C1x6 H2x6 O1x6
C6H12O6
Practice Problems:• A sample has been analyzed to be 10.04 % C, 0.84
% H & 89.12% Cl. Find the Empirical Formula.
• A compound’s empirical formula has been determined to be HF. The compound’s molar mass is 40 g/mol. What is its chemical formula?
• A compound’s empirical formula has been determined to be CH2. The compound’s molar mass is 42 g/mol. What is its chemical formula?