Transcript AP Notes Chapter 3

AP Notes Chapter 2
Molecules, Ions and Their Compounds
Chemical Compounds
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Chemical compounds result from the joining
together of atoms
Chemical Bonds are the forces that hold
atoms together.
Chemical formulas are used to describe the
number and kind of atoms in a compound
There are two major types of compounds
that differ mostly by the way the atoms
hold on to each other or the type of bond.
Ionic Compounds
•Ionic compound are held together with an
Ionic bond joining metal ions and non metal
ions
•Transfer of electrons cause the formation of
ions or charged particles
Ions & Ionic Compounds
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Atoms or groups of atoms with a charge.
Cations- positive ions - get by losing
electrons(s). Metallic
Anions- negative ions - get by gaining
electron(s). Nonmetallic
It is these opposite charges that define an
ionic compound and an ionic bond
Solid Ionic compounds are called salts.
+1+2
-3 -2 -1
Ionic Compounds
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Law of Definite Proportion- compounds
have a constant composition.
Ions react in specific ratios by mass and
charge.
Ionic compounds do not have a charge
Positive and negative charges balance
Ions exist in small whole number ratios.
Get charges from table, name of metal
ion, or memorized from the list.
Use parenthesis to indicate multiple
polyatomics.
Naming Ionic Compounds
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Cation is wrtiten first in name and
formula.
If the cation is monoatomic- Name the
metal (cation) just write the name.
If the cation is polyatomic- name it.
THEN If the anion is monoatomic- name it
but change the ending to –ide.
If the anion is poly atomic- just name it
Practice Ion names and formula w/charge
Naming Ionic Compounds
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Have to know what ions they form
off table, polyatomic, or figure it out
CaS
Calcium sulfide
K2S
Potassium sulfide
AlPO4
Aluminum phosphate
K2SO4
FeS
CoI3
Potassium sulfate
Iron II sulfide or Ferrous sulfide
Cobalt III iodide or Cobaltic iodide
Naming Ionic Compounds
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Fe2(C2O4)
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MgO
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MnO
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KMnO4
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NH4NO3
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Hg2Cl2
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Cr2O3
Writing Ionic Formulas
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Sodium nitride
sodium- Na is always +1
Nitride - ide tells you it comes from the
table
nitride is N-3
Doesn’t add up to zero.
+1
Na
-3
N
Writing Ionic Formulas
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Sodium nitride
sodium- Na is always +1
nitride - ide tells you it comes from the
table
nitride is N-3
Doesn’t add up to zero
Need 3 Na
+1
Na
-3
N
Na3N
Ionic Compound Formulas
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Sodium sulfite
calcium iodide
Lead (II) oxide
Lead (IV) oxide
Mercury (I) sulfide
Barium chromate
Aluminum hydrogen
Cerium (IV) nitrite
Na2S
CaI2
PbO
Pb2O4 or PbO2
Hg2S
BaCrO4
sulfate Al(HSO4)3
Ce(NO3)4
Covalent Compounds
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Composed of Molecules
Law of Multiple Proportions- When two elements
form more than one compound, the ratios of the
masses of the second element that combine with
one gram of the first can be reduced to small
whole numbers.
Chemical formula- the number and type of
atoms in a molecule.
C2H6 - 2 carbon atoms, 6 hydrogen atoms
Structural formula shows the connections, but
not necessarily the shape.
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Molecules differ by the number and kind
of elements that make them up
Speculate on the formula of two oxides of
carbon and oxygen
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Carbon monoxide = CO
Carbon dioxide
= CO2
Show that these compounds follow the
law of multiple proportion.
Sometimes formula is not enough to get
an adequate picture of a compound
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There are also other models that attempt
to show three dimensional shape.
Ball and stick.
H
H C
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Ball and stick.
H
H
C H
H
Covalent compounds
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Two words, with prefixes.
Prefixes tell you how many.
mono, di, tri, tetra, penta, hexa, septa,
nona, deca
First element whole name with the
appropriate prefix, except mono.
Second element, -ide ending with
appropriate prefix.
Practice
Naming Covalent Compounds
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Two words, with prefixes
Prefixes tell you how many.
mono, di, tri, tetra, penta, hexa, septa,
nona, deca
First element whole name with the
appropriate prefix, except mono
Second element, -ide ending with
appropriate prefix
Practice
Naming Covalent Compounds
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CO2
CO
CCl4
N2O4
XeF6
N4O4
P2O10
Covalent compounds
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The name tells you how to write the
formula
Sulfur dioxide
difluorine monoxide
nitrogen trichloride
diphosphorus pentoxide
Summary for Writing Formulas
and Names of Compounds
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Two sets of rules, ionic and covalent
To decide which to use, decide what the
first word is.
If is a metal or polyatomic use ionic.
If it is a non-metal use covalent.
Acids
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Substances that produce H+ ions when
dissolved in water.
All acids begin with H.
Two types of acids:
Oxyacids
Non-oxyacids
Naming acids
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If the formula has oxygen in it
write the name of the anion, but change
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ate to -ic acid
ite to -ous acid
Watch out for sulfuric and sulfurous
H2CrO4
HMnO4
HNO2
Naming acids
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If the acid doesn’t have oxygen
add the prefix hydrochange the suffix -ide to -ic acid
HCl
H2S
HCN
Formulas for acids
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Backwards from names.
If it has hydro- in the name it has no
oxygen
Anion ends in -ide
No hydro, anion ends in -ate or -ite
Write anion and add enough H to balance
the charges.
Formulas for acids
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hydrofluoric acid
dichromic acid
carbonic acid
hydrophosphoric acid
hypofluorous acid
perchloric acid
phosphorous acid
Percent Composition
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Percent of each element a compound is
composed of.
Find the mass of each element, divide by
the total mass, multiply by a 100.
Easiest if you use a mole of the
compound.
Find the percent composition of CH4
Al2(Cr2O7)3
CaSO4 · 2H2O
Working backwards
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From percent composition, you can
determine the empirical formula.
Empirical Formula the lowest ratio of
atoms in a molecule.
Based on mole ratios.
A sample is 59.53% C, 5.38%H,
10.68%N, and 24.40%O what is its
empirical formula.
Sample Problem
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A 0.2000 gram sample of a compound
(vitamin C) composed of only C, H, and O
is burned completely with excess O2 .
0.2998 g of CO2 and 0.0819 g of H2O are
produced. What is the empirical formula?
Empirical To Molecular Formulas
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Empirical is lowest ratio.
Molecular is actual molecule.
Need Molar mass.
Ratio of empirical to molar mass will tell
you the molecular formula.
Must be a whole number because...
Sample Problem
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A compound is made of only sulfur and
oxygen. It is 69.6% S by mass. Its molar
mass is 184 g/mol. What is its formula?
Hydrates
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Some salts trap water crystals when they
form crystals.
These are hydrates.
Both the name and the formula needs to
indicate how many water molecules are
trapped.
In the name we add the word hydrate
with a prefix that tells us how many water
molecules.
Hydrates
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In the formula you put a dot and then
write the number of molecules.
Calcium chloride dihydrate
CaCl22O
Chromium (III) nitrate hexahydrate
Cr(NO3)3 6H2O