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Modern ChemistryModern ChemistryChapter 7Chapter 7
Chemical Formulas and Chemical Formulas and Chemical CompoundsChemical Compounds
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Section 1
Chemical Namesand Formulas
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Molecular compounds – for one molecule
Ionic compounds – for one formula unit; the simplest ratio of cations to anions
Chemical Formula
Eight carbon atoms in the
molecule
Eighteen hydrogen atoms in the molecule
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5 ions – two Al 3+ ions and three (SO4) 2-
ions
Chemical Formula
2 Al atoms
4 O atoms4 SO4 ions
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• Binary Compound – compound with only two types of atoms
• Nomenclature – a naming system• Salt- an ionic compound
composed of a cation and an anion from an acid
Definitions
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• Monatomic ions – ions formed from a single atom
• For negative monatomic ions, -ide is added to the root name
Definitions
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Ionic compounds contain
a metal and a nonmetal or
a polyatomic ion !!!
How can I tell if the compound is ionic or
covalent ????
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Ionic Compounds
Writing Fomulas and Naming
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1+
2+3+ 3-2-1-
Charges on Monatomic Ions
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Ag 1+Zn 2+Cu 1+ or 2+Fe/Cr2+ or 3+Sn 2+ or 4+Pb 2+ or 4+See list.
Charges on Transition Metals
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PbO2 and PbOCharges of Metals
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Polyatomic Ions Page 226
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Formulas1. Write the symbols2. Determine the charges
1. Monatomic ions from the periodic table
2. Transition metals from a roman numeral
3. Polyatomic ions from sheet.
3. Cross the charges.4. Reduce to lowest ratio.
Ionic Compounds
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Names1. Write the cation name.2. Write the anion name.
• Add –ide to the anion if monatomic
3. Add the roman numeral for any transition metal.
4. NO PREFIXES!!!!
Ionic Compounds
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(charge x subscript)+(charge x subscript) = 0
Ionic Binary CompoundsAluminum Oxide
3+ 2-
(3+ x ) + (2- x ) = 02 3
Al2O3
FO
RM
ULA
S
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Ionic Binary CompoundsAluminum Oxide
3+ 2-
Al2O3
FO
RM
ULA
S
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Mg3N2
Magnesium
Ionic BinaryCompoundsN
AM
ING
Nitrogen
ide
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Pra
cti
ce P
ag
e 2
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1. Write formulas for the binary ionic compounds formed between the following elements:a. potassium and iodineb. magnesium and chlorine c. sodium and sulfurd. aluminum and sulfure. aluminum and nitrogen
2. Name the binary ionic compounds indicated by the following formulas:a. AgCl e. BaOb. ZnO f. CaCl2c. CaBr2
d. SrF2
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Iron (III) Chloride
3+ 1-
(3+ x ) + (1- x ) = 01 3
FeCl3
Ionic Compounds with Transition MetalsF
OR
MU
LAS
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Tin (II) Oxide
2+ 2-
(2+ x ) + (2- x ) = 01 1
SnO
Ionic Compounds with Transition MetalsF
OR
MU
LAS
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Tin (II) Oxide
2+ 2-
SnO
Ionic Compounds with Transition MetalsF
OR
MU
LAS
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Pra
cti
ce P
ag
e 2
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1. Write the formula and give the name for the compounds formed between the following ions:a. Cu 2+ and Br − d. Hg 2+ and S 2−
b. Fe 2+ and O 2− e. Sn 2+ and F −
c. Pb 2+ and Cl − f. Fe 3+ and O 2−
2. Give the names for the following compounds:a. CuO c. SnI4b. CoF3 d. FeS
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PbO
Lead
Ionic Compounds with Transition Metals
NA
MIN
G
OxygenideII
( x 1 ) + ( 2- x 1 ) = 02+
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Ionic Compounds with Polyatomic Ions
Ammonium Sulfate+ 2-
(1+ x ) + (2- x ) = 02 1
(NH4)2SO4Parenthesis are needed if the p. ion has a subscript from the crossed charge – outside
the ( ).
FO
RM
ULA
S
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Ca(NO3)2
Calcium
Ionic Compounds with Polyatomic Ions
NA
MIN
G
Nitrate
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Pra
cti
ce P
ag
e 2
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1. Write formulas for the following ionic compounds:a. sodium iodide e. copper(II) sulfateb. calcium chloride f. sodium carbonatec. potassium sulfide g. calcium nitrited. lithium nitrate h. potassium perchlorate
2. Give the names for the following compounds:a. Ag2O
b. Ca(OH)2
c. KClO3
d.NH4OH
e. Fe2(CrO4)3
f. KClO
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Molecular Compounds
Writing Fomulas and Naming
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Pre
fixes f
or
Covale
nt
p. 228
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Formulas1. Write the symbols.2. Use prefixes for subscripts.3. DON’T reduce.
Molecular Compound
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Names1. Write the name of the elements.
– Order: Smaller group number first;– Same group? Greater period
number first.
2. Add –ide to the second element.3. Add prefixes to each element for
the number of atoms.
Molecular Compound
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Disulfur difluoride
S2F2
Binary Molecular CompoundsF
OR
MU
LAS
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nitrogen
Binary Molecular CompoundsN
AM
ING
oxygenidedi tetra
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Pra
cti
ce P
ag
e 2
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1. Name the following binary molecular compounds:
a. SO3
b. ICl3c. PBr5
2. Write formulas for the following compounds:
a. carbon tetraiodideb. phosphorus trichloridec. dinitrogen trioxide
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• Acids – Chapter 14• Binary Acids – two elements;
hydrogen and one other element• Oxyacids – contain hydrogen, one
other element and oxygen• Acid – typically thought of as an H
donor; usually referred to as a solution of the compound in water.
Acids and Salts
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• Salt – an ionic compound• Made from
– the cation of a base and– the anion of an acid
• Some retain an H in the anion– Example: CO3
2- carbonate
HCO3 1- hydrogen
carbonate or bicarbonate
Acids and Salts
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Salt
Defi
nit
ion
An
imati
on
p. 230
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Lis
t of
Acid
s
p. 230
Know these acids:
HF, HCl, H3PO4, HNO3, H2SO4 CH3COOH
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Section 3
Oxidation Numbers
Oxidation Numbers• Oxidation numbers are numbers assigned
to the atoms in a molecular compound or ion that indicates the general distribution of electrons among bonded atoms.
• Oxidation numbers are not actual charges.
• Oxidation numbers can be useful in naming compounds and writing formulas.
+2-1
+3+1
-2
Rules for Assigning Oxidation Numbers
– Atoms in a pure element have an oxidation number of zero – O2 Ox. # = 0
– Fluorine always has ox. # of -1– Oxygen almost always has ox. # of
-2 except in peroxides such as H2O2
– then it is a -1.
Rules for Assigning Oxidation Numbers
• (Rules continued):– Hydrogen’s ox. # is +1 unless it is
with metals – then it is -1– The sum of the ox. # in molecules
must be zero, but in polyatomic ions, it is equal to the ions charge.
Oxidation Numbers• What are the oxidation numbers for each
atom in these compounds?UF6 : Fluorine is -1 x 6 = -6
Uranium +6 {+6 + (-6)} = 0
H2SO4 : Oxygen is -2 (x 4 = -8)Hydrogen is +1 (x 2 = +2)
soSulfur has to be +6
{ (+6) + (+2) + (-8) }= 0
Oxidation Numbers
• What are the oxidation numbers for the chlorate polyatomic ion?
ClO3- : Oxygen is -2 x 3 = -6
Chlorine must be +5 { (+5) + (-6)} = -1 (the ion’s
charge)
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Section 4
Using Chemical Formulas
Formula Mass
• With a chemical formula, you can calculate many characteristic values for a compound.
• Formula Mass: – Compounds have masses – just
like elements.
Formula Mass
• Formula Mass: – The formula mass of any molecule,
formula unit, or ion is the sum of the average atomic masses of all the atoms represented in its formula.
– To find the mass of a compound simply add the masses of the atoms that make up the compound. Units are amu’s.
Formula Mass
• To find the formula mass of sulfuric acid (H2SO4):
element # of atoms x mass (to 2 decimals)
H 2 1.01 = 2.02 amuS 1 32.01=32.01 amuO 4 16.00=64.00 amu
98.03 amu
Formula Mass
• To find the formula mass of Calcium Nitrate Ca(NO3)2
element # of atoms x mass = Ca 1 40.08 =40.08 amuN 2 14.01 =28.02 amuO 6 16.00= 96.00 amu
164.10 amu
Molar Mass
• Molar Mass– The mass of a mole of any substance
is equal to its formula mass – except instead of amu’s it is in grams.
– Formula mass of sulfuric acid = 98.03 amu
– Molar mass of sulfuric acid = 98.03 grams
Molar Mass
• To find the molar mass of Calcium Nitrate Ca(NO3)2
element # of atoms x mass = Ca 1 40.08 =40.08 gN 2 14.01 =28.02 gO 6 16.00= 96.00 g
164.10 g
Percentage Composition
• It is sometimes useful to know what the percentage of a compound is an element.
• What percentage of water is oxygen?H: 1.01 x 2 = 2.02
O: 16.0 x 1 = 16.0
Molar Mass= 18.02 g
16.0 ÷18.02 = 88.79%
Molar Mass
• Molar Mass can be used as a conversion factor.
1 mole H2SO498.03 grams
1 mole H2SO4
98.03 gramsor
Problems
• How many moles are there in 25 g of H2SO4?
1 mole H2SO498.03 grams
25 g H2SO4 x = 0.255 mol
Problems
• What is the mass of 4.2 moles of H2SO4?
98.03 g H2SO41 mol H2SO4
4.2 mol H2SO4
x = 411.73 mol
Problems
• How many molecules are in 54 g of H2SO4?
6.02 x 1023 molecules H2SO498.03 g H2SO4
54 g H2SO4 x =
3.32 x 1023 molecules
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Section 4
Determining Chemical Formulas
Chemical Formula from % Comp
• Check periodic table for molar masses of each element
• Find moles of each element present (assume 100g since we are working with percentages)
• To determine the simplest ratio of moles in the compound, select the smallest number of moles calculated and divide the other moles calculated by that number
• Write the formula using the smallest whole number ratio of elements
Empirical formulas
• Simplest formula• Consists of element symbols and
subscripts showing the numbers of each element
• Really, subscripts represent the smallest whole number ratios
Empirical formulas
What is the empirical formula of a compound containing 56.6% K, 8.7% C and 34.7 % O ?
K= 39.10 g/molC = 12.01 g/molO = 16.00 g/mol
Empirical formulas
K 56.6 g K x 1 mol K = 1.45 mol 39.10 g K C 8.7 g C x 1 mol C = 0.724 mol 12.01 g CO 34.7 g O x 1 mol O = 2.17 mol 16.00 g OSmallest value = 0.724 Divide all
answers by this number.
Empirical formulas
K = 1.45 mol = 2.00 0.724 molC = 0.724 mol = 1.00 0.724 molO = 2.17 mol = 3.00 0.724 molTherefore, the empirical formula = K2CO3
Name? Potassium Carbonate
Molecular formulas
• Gives the type and actual number of atoms in the compound
• CH2O – empirical formula for glucose
• C6H12O6 – molecular formula for glucose
• So far, we have been studying ionic compounds, so molecular and empirical formulas were the same
• In most compounds, however, not the same
Molecular formulas
• Molecular formulas can be determined from empirical formulas
X (empirical formula) = molecular formula
(X is a whole number)
Also true . . .Molecular molar mass = XEmpirical molar mass
Molecular formulas
Empirical formula of mercury (I) chloride is HgCl. What is the molecular formula, knowing that molar mass is 472.08 g/mol?
Empirical formula HgClMolar mass of unknown = 472.08
g/mol1 mol Hg = 200.59 g/mol1 mol Cl = 35.45 g/molMolar mass of HgCl = 236.04 g/mol
Molecular formulas
472.08 g/mol = 2.00236.04 g/mol2(HgCl) = Hg2Cl2