molecules, compounds, and chemical equations chemistry... · in a chemical formula, the sum of the...
Post on 28-Jul-2018
216 Views
Preview:
TRANSCRIPT
3.2 CHEMICAL BONDS
Compounds are composed of atoms held
together by chemical bonds.
Chemical bonds result from the attractions
between the charged particles (the electrons
and protons) that compose atoms.
Chemical bonds are classified into two types:
Ionic
Covalent
IONIC BONDS
Ionic bonds—which occur between metals
and nonmetals—involve the transfer of
electrons from one atom to another.
When a metal interacts with a nonmetal, it
can transfer one or more of its electrons to
the nonmetal.
The metal atom then becomes a cation.
The nonmetal atom becomes an anion.
IONIC BONDS
These oppositely charged ions attract one
another by electrostatic forces and form an
ionic bond.
The result is an ionic compound, which in
the solid phase is composed of a lattice—a
regular three-dimensional array—of
alternating cations and anions.
COVALENT BONDS
Covalent bonds—which occur between two or
more nonmetals—involve the sharing of
electrons between two atoms.
When a nonmetal bonds with another nonmetal,
neither atom transfers its electron to the other.
Instead the bonding atoms share some of their
electrons.
The covalently bound atoms compose a
molecule.
Hence, we call covalently bonded compounds
molecular compounds.
3.3 REPRESENTING COMPOUNDS:
CHEMICAL FORMULAS
A compound is represented with its chemical
formula.
Chemical formula indicates the elements
present in the compound and the relative
number of atoms or ions of each.
Water is represented as H2O.
Carbon dioxide is represented as CO2.
Sodium Chloride is represented as NaCl.
Carbon tetrachloride is represented as CCl4.
Problem 23 on page 130
TYPES OF CHEMICAL FORMULAS
Chemical formulas can generally be
categorized into three different types:
Empirical formula
Molecular formula
Structural formula
TYPES OF CHEMICAL FORMULAS
An empirical formula gives the relative
number of atoms of each element in a
compound. (Lowest whole # ratio)
A molecular formula gives the actual number
of atoms of each element in a molecule of a
compound.
(a) For C4H8, the greatest common factor is 4.
The empirical formula is therefore CH2.
(b) For B2H6, the greatest common factor is 2.
The empirical formula is therefore BH3.
(c) For CCl4, the only common factor is 1, so the
empirical formula and the molecular formula
are identical.
TYPES OF CHEMICAL FORMULAS
A structural formula uses lines to represent
covalent bonds and shows how atoms in a
molecule are connected or bonded to each
other. The structural formula for H2O2 is
shown below:
Learn more about in chapter 10!!!
A molecular model is a more
accurate and complete way to
specify a compound.
A ball-and-stick molecular model
represents atoms as balls and
chemical bonds as sticks; how
the two connect reflects a
molecule’s shape.
The balls are typically color-
coded to specific elements.
Problem 25 on page 130
MOLECULAR MODELS
MOLECULAR MODELS
In a space-filling molecular model, atoms fill the space between each other to more closely represent our best estimates for how a molecule might appear if scaled to visible size.
3.4 AN ATOMIC-LEVEL VIEW OF ELEMENTS
AND COMPOUNDS
Elements may be either atomic or molecular.
Compounds may be either molecular or ionic.
VIEW OF ELEMENTS AND COMPOUNDS
Atomic elements exist in nature with single
atoms as their basic units. Most elements fall
into this category.
Examples are Na, Ne, C, K, Mg, etc.
Molecular elements do not normally exist in
nature with single atoms as their basic units;
instead, they exist as molecules—two or more
atoms of the element bonded together.
There only seven diatomic elements and they are H2, N2,
O2, F2, Cl2, Br2, and I2. (HOFBrINCl)
Also, P4 and S8 are polyatomic elements.
MOLECULAR COMPOUNDS
Molecular compounds are usually composed
of two or more covalently bonded nonmetals.
The basic units of molecular compounds are
molecules composed of the constituent
atoms.
Water is composed of H2O molecules.
Dry ice is composed of CO2 molecules.
Propane (often used as a fuel for grills) is composed
of C3H8 molecules.
IONIC COMPOUNDS
Ionic compounds are composed of cations
(usually a metal) and anions (usually one
or more nonmetals) bound together by
ionic bonds.
The basic unit of an ionic compound is the
formula unit, the smallest, electrically neutral
collection of ions.
The ionic compound table salt, with the formula
unit NaCl, is composed of Na+ and Cl– ions in a
one-to-one ratio.
3.5 IONIC COMPOUNDS: FORMULAS AND
NAMES Summarizing Ionic Compound Formulas:
Ionic compounds always contain positive and
negative ions.
In a chemical formula, the sum of the charges of
the positive ions (cations) must equal the sum of
the charges of the negative ions (anions).
+ = -
The formula of an ionic compound reflects the
smallest whole-number ratio of ions.
IONIC COMPOUNDS: FORMULAS AND
NAMES The charges of the representative elements
can be predicted from their group numbers.
The representative elements forms only one
type of charge.
Transition metals tend to form multiple types
of charges.
Hence, their charge cannot be predicted as in
the case of most representative elements.
Ionic compounds can
be categorized into two
types, depending on
the metal in the
compound.
The first type contains
a metal whose charge
is the same from one
compound to another.
Whenever the metal in
this first type of
compound forms an
ion, the ion always has
the same charge.
NAMING IONIC COMPOUNDS
NAMING BINARY IONIC COMPOUNDS OF
TYPE I CATIONS
Binary compounds contain only two different
elements. The names of binary ionic
compounds take the following form:
NAMING TYPE I BINARY IONIC COMPOUNDS
For example, the name for KCl consists of the
name of the cation, potassium, followed by
the base name of the anion, chlor, with the
ending -ide.
KCl is potassium chloride.
The name for CaO consists of the name of the
cation, calcium, followed by the base name of
the anion, ox, with the ending -ide.
CaO is calcium oxide.
BASE NAMES OF MONOATOMIC ANIONS
The base names of some nonmetals, and their most common charges in ionic compounds, are shown in Table 3.3.
NAMING TYPE II IONIC COMPOUNDS
The second type of ionic compound contains
a metal with a charge that can differ in
different compounds.
The metals in this second type of ionic
compound can form more than one kind of
cation (depending on the compound).
Its charge must therefore be specified for a
given compound.
TYPE II IONIC COMPOUNDS
Iron, for instance, forms a 2+ cation in some
of its compounds and a 3+ cation in others.
Metals of this type are often transition
metals.
FeS Here iron is +2 cation (Fe2+).
Fe2S3 Here iron is +3 cation (Fe3+).
Cu2O Here copper is +1 cation (Cu+).
CuO Here copper is +2 cation (Cu2+).
Some main group metals, such as Pb, Tl, and Sn,
form more than one type of cation.
NAMING TYPE II BINARY IONIC
COMPOUNDS
For these types of metals, the name of the
cation is followed by a roman numeral (in
parentheses) that indicates the charge of
the metal in that particular compound.
For example, we distinguish between Fe2+ and
Fe3+ as follows:
Fe2+ Iron(II)
Fe3+ Iron(III)
NAMING TYPE II BINARY IONIC
COMPOUNDS The full names for compounds containing
metals that form more than one kind of
cation have the following form:
The charge of the metal cation can be determined by
inference from the sum of the charges of the nonmetal.
NAMING TYPE II BINARY IONIC
COMPOUNDS For example, to name CrBr3 determine the
charge on the chromium.
Total charge on cation + total anion charge = 0.
Cr charge + 3(Br– charge) = 0.
Since each Br has a –1 charge, then
Cr charge + 3(–1) = 0
Cr charge –3 = 0
Cr = +3
Hence, the cation Cr3+ is called chromium(III), while
Br– is called bromide.
Therefore, CrBr3 is chromium(III) bromide.
POLYATOMIC ION
Many common ionic compounds contain
ions that are themselves composed of a
group of covalently bonded atoms with an
overall charge.
This group of charged species is called
polyatomic ions.
NaNO3 contains Na+ and NO3–.
CaCO3 contains Ca2+ and CO32–.
KClO Contains K+ and ClO–.
NAMING IONIC COMPOUNDS CONTAINING
POLYATOMIC IONS
We name ionic compounds that contain a
polyatomic ion in the same way as other ionic
compounds, except that we use the name of
the polyatomic ion whenever it occurs.
For example, NaNO2 is named according to
its cation, Na+, sodium, and
its polyatomic anion, NO2–, nitrite.
Hence, NaNO2 is sodium nitrite.
OXYANIONS
Most polyatomic ions are oxyanions, anions
containing oxygen and another element.
Notice that when a series of oxyanions contains
different numbers of oxygen atoms, they are
named according to the number of oxygen
atoms in the ion.
If there are two ions in the series, the one with more oxygen atoms has the ending -ate, and
the one with fewer has the ending -ite.
For example, NO3
– is nitrate SO42– is sulfate
NO2– is nitrite SO3
2– is sulfite
OXYANIONS
If there are more than two ions in the series
then the prefixes hypo-, meaning less than,
and per-, meaning more than, are used.
ClO– hypochlorite BrO– hypobromite
ClO2– chlorite BrO2
– bromite
ClO3– chlorate BrO3
– bromate
ClO4– perchlorate BrO4
– perbromate
AGENDA FOR WEDNESDAY
Check problems 35, 36, 41-44
Return polyatomic ion quizzes
Return test and discuss test corrections
More review on ionic compounds
Hydrated compounds
Check answers on worksheet.
Questions
Quick Review
Hydrated compounds
Molecular Compounds
Naming Acids
Write the names for the following compounds:
NaBr SrS
Mg3P2 Ti(SO4)2
FePO4 K3N
NH4I CoCO3
ZnI2 Mn(NO3)3
CuOH Zn(NO2)2
Write the formulas for the following chemical
compounds:
nickel (III) sulfide
manganese (II) phosphate
silver acetate
potassium carbonate
ammonium oxide
tin (IV) selenide
lead (IV) sulfite
copper (II) bicarbonate
sodium phosphide
QUICK REVIEW
Write the names for the following compounds:
Mg3P2 FePO4
Mn(NO3)3 NH4I CuOH Zn(NO2)2
Write the formulas for the following chemical compounds:
nickel (III) sulfide
manganese (II) phosphate
silver acetate
potassium carbonate
HYDRATED IONIC COMPOUNDS
Hydrates are ionic compounds containing a
specific number of water molecules
associated with each formula unit.
For example, the formula for epsom salts is
MgSO4 • 7H2O.
Its systematic name is magnesium sulfate
heptahydrate.
CoCl2 • 6H2O is cobalt(II)chloride hexahydrate.
Common hydrate prefixes
hemi = ½
mono = 1
di = 2
tri = 3
tetra = 4
penta = 5
hexa = 6
hepta = 7
octa = 8
Other common hydrated
ionic compounds and their
names are as follows:
CaSO4 • 1/2H2O is called calcium
sulfate hemihydrate.
BaCl2 • 6H2O is called barium
chloride hexahydrate.
CuSO4 • 6H2O is called copper
sulfate hexahydrate.
Do Problems 45 and 46 on page
131.
HYDRATES
BINARY MOLECULAR COMPOUNDS
(COVALENT COMPOUNDS)
No ions form
Elements share electrons
ALWAYS between two nonmetals
Use prefixes to indicate the # of atoms
present
MOLECULAR (COVALENT) COMPOUNDS
mono = 1 hexa = 6
di = 2 hepta = 7
tri = 3 octa = 8
tetra = 4 nona = 9
penta = 5 deca = 10
NAMING COVALENT COMPOUNDS
Prefixes are always used to indicate the number
of atoms
Only time a prefix is not used mono- for the first
element.
So, if only one of the first element then no prefix is
used
If the numerical prefix ends with the letter a or o
and the name of the element begins with an a or
o the last letter of the prefix is dropped.
WRITING FORMULAS FROM NAMES
Use prefixes to tell you how many of each atom
you need in the formula.
DO NOT SIMPLIFY!!!!
ACIDS
Acids are molecular compounds that release
hydrogen ions (H+) when dissolved in water.
Acids are composed of hydrogen, usually
written first in their formula, and one or more
nonmetals, written second.
HCl is a molecular compound that, when
dissolved in water, forms H+(aq) and Cl–(aq) ions,
where aqueous (aq) means dissolved in water.
ACIDS
Acids are molecular compounds that form H+
when dissolved in water.
To indicate the compound is dissolved in water (aq) is
written after the formula.
A compound is not considered an acid if it does not
dissolve in water.
Sour taste
Dissolve many metals
such as Zn, Fe, Mg; but not Au, Ag, Pt
Formula generally starts with H
e.g., HCl, H2SO4
Binary acids have H+1 cation and nonmetal anion.
Oxyacids have H+ cation and polyatomic anion.
ACIDS
NAMING BINARY ACIDS
Write a hydro- prefix.
Follow with the nonmetal name.
Change ending on nonmetal name to –ic.
Write the word acid at the end of the name.
REVIEW
Silicon Dioxide Copper (II) Bicarbonate
Sodium Phosphide Arsenic Pentachloride
Selenium Tetrafluoride Lead (IV) Sulfite
PCl3` Cl2O7
Al2O3 Ba3P2
Fe(OH)3 Mg(NO2)2
SF6 N2O3
ACIDS
Anion doesn’t contain oxygen
Prefix hydro-
Name anion
Suffix –ic
Add acid
HCl (aq)
H2S (aq)
HBr (aq)
HF (aq)
Notice the formulas have a zero charge. Like ionic compounds
NAMING OXYACIDS
If polyatomic ion name ends in –ate, then
change ending to –ic suffix.
If polyatomic ion name ends in –ite, then
change ending to –ous suffix.
Write word acid at the end of all names.
oxyanions ending with -ate
oxyanions ending with -ite
ACIDS
Anion contains oxygen-Polyatomic Ions
Name formed from the root name of the anion with a
suffix –ic or –ous
Anion ends in –ate change to –ic
I ate something icky.
Anion ends in –ite change to –ous
I took a bite of something delicious.
H3PO4 (aq)
H2SO4 (aq)
H2SO3 (aq)
HNO3 (aq)
HNO2 (aq)
Stem changes to:
Sulfide Hydrosulfuric acid
Sulfate Sulfur Sulfuric acid
Sulfite Sulfurous acid
Phosphate Phosphor Phosphoric acid
Phosphite Phosphorous acid
Anion Ending Acid Name
-ide hydro-(stem)-ic acid
-ate (stem)-ic acid
-ite (stem)-ous acid
ACID NOMENCLATURE REVIEW
No Oxygen
w/Oxygen
hydrosulfuric acid
chloric acid
acetic acid
1. H2S (aq)
2. HClO3 (aq)
3. HC2H3O2 (aq)
Name the Following
WRITING FORMULAS FOR ACIDS
When name ends in acid, formulas starts with H.
Write formulas as if ionic, even though it is
technically molecular. (H is a nonmetal that forms
an ion in solution)
Hydro- prefix means it is binary acid; no prefix
means it is an oxyacid.
For oxyacid
if ending is –ic, polyatomic ion ends in –ate.
if ending is –ous, polyatomic ion ends in –ite.
Make sure to include the (aq) after the formula.
Do problems 51-54.
Do problems 55-58.
Assignments
Test corrections due on Monday!
Types of compounds WS (front and back) due
Tuesday.
Extra credit WS due on Tuesday.
Read and take notes on pages 107-116 for
Monday.
Naming Acid Ws due before you can got to lunch.
Turn in test corrections, make sure to staple your
original tests to your corrections.
Get out naming acids nomenclature WS-just going
to check answers
Reminders
Types of compounds WS (front and back) due
tomorrow.
Extra credit WS due tomorrow.
MOLAR MASS
Molar Mass-the mass in grams of one mole of
the compound (molecular weight)
Obtained by summing the masses of the
component atoms in the compound.
CH4-breaks down into
1 mol C= 12.01 grams
4 mol H = 4 x 1.008 grams =4.032 grams
1 mol CH4 = 16.04 grams
1 mol of element = grams (mass on the periodic
table)
1 mol of a compound = 6.022 x 1023 molecules of
that compound
1 mol of an element = 6.022 x 1023 atoms
1 mol of a compound = molar mass
Compounds are made of elements
Molecules Atoms
Molecules are made up of atoms
PERCENT COMPOSITION
Percentage by mass of elements in a compound –
mass % (weight percent)
Determined by comparing the mass of the
element in 1 mole of the compound to the total
mass of 1 mole of the compound multiplied by
100. Mass percent of element = mass of element in 1 mole of compound x 100 mass of 1 mol of compound
The percentages of each element in the compound should add up to 100% if done
correctly. A way to check your work.
DETERMINING THE FORMULA OF A COMPOUND
Empirical formula-simplest formula for a compound that
shows the atomic ratio of the elements in the compound
Empirical formula lowest whole # ratio
Simplest form
Molecular formula- the actual formula of a molecular
substance that gives the ratio of atoms of each element to
the substances molecules
Molecular formula can be a higher whole # ratio than the
empirical formula must compare the molar mass of the
compound and the mass of the empirical formula you
determined
Sometimes the empirical and molecular formula will be the
same!!!!
HOW TO FIND THE EMPIRICAL FORMULA
FROM % COMPOSITION DATA. 1. Change the % to grams(assume dealing with a
100.0 gram sample)
2. For each element convert the # of grams of each
element into moles using molar mass
3. Get a ratio by dividing all the mole values by the
smallest number of moles
4. Need ratios to be in whole numbers so may need
to multiply to get a whole number-these values will
be the subscripts in our formula
If given grams then skip step one to determine the
empirical formula.
DETERMINING THE MOLECULAR FORMULA
Obtain empirical formula
Compute the mass that corresponds to that formula
Calculate the ratio
Molar Mass (given to you) = x
Empirical formula Mass
Multiply the empirical formulas subscripts by
“x” to get the molecular formula (can be 1)
CHEMICAL REACTIONS
Reactions involve chemical changes in matter
resulting in new substances.
Reactions involve rearrangement and
exchange of atoms to produce new
molecules.
Reactants Products
CHEMICAL EQUATIONS
Shorthand way of describing a reaction
Provide information about the reaction
Formulas of reactants and products
States of reactants and products
Relative numbers of reactant and product
molecules that are required
Can be used to determine weights of reactants
used and products that can be made
COMBUSTION OF METHANE
Methane gas burns to produce carbon dioxide gas and gaseous water.
Whenever something burns it combines with O2(g).
CH4(g) + O2(g) CO2(g) + H2O(g)
If you look closely, you should immediately
spot several problems.
To correct these problems, we must balance
the equation by adding coefficients, not
changing the subscripts.
COMBUSTION OF METHANE, BALANCED
To show the reaction obeys the Law of
Conservation of Mass the equation must be
balanced.
We adjust the numbers of molecules so there
are equal numbers of atoms of each element on
both sides of the arrow.
1 C + 4 H + 4 O 1 C + 4 H + 4 O
ORGANIC COMPOUNDS
Early chemists divided compounds into two
types: organic and inorganic.
Compounds from living things were called
organic; compounds from the nonliving
environment were called inorganic.
Organic compounds are easily decomposed
and could not be made in the lab.
Inorganic compounds are very difficult to
decompose, but are able to be synthesized.
MODERN ORGANIC COMPOUNDS
Today organic compounds are commonly
made in the lab and we find them all around
us.
Organic compounds are mainly made of C
and H, sometimes with O, N, P, S, and trace
amounts of other elements
The main element that is the focus of organic
chemistry is carbon.
CARBON BONDING
Carbon atoms bond almost exclusively
covalently.
Compounds with ionic bonding C are generally
inorganic.
When C bonds, it forms four covalent bonds:
4 single bonds, 2 double bonds, 1 triple + 1 single,
etc.
Carbon is unique in that it can form limitless
chains of C atoms, both straight and
branched, and rings of C atoms.
HYDROCARBONS
Organic compounds can be categorizing into
types: hydrocarbons and functionalized
hydrocarbons.
Hydrocarbons are
organic compounds
that contain only
carbon and hydrogen.
Hydrocarbons
compose common
fuels such as
oil,
gasoline,
liquid propane gas,
and natural gas.
HYDROCARBONS
Hydrocarbons containing
only single bonds are
called alkanes,
while those containing
double or triple bonds are
alkenes and alkynes,
respectively.
Hydrocarbons consist of a
base name and a suffix.
alkane (-ane)
alkene (-ene)
alkyne (-yne)
The base names for a
number of
hydrocarbons are listed
here:
1 meth 2 eth
3 prop 4 but
5 pent 6 hex
7 hept 8 oct
9 non 10 dec
NAMING OF HYDROCARBONS
Base name
determined by
number of C atoms
Suffix
determined by
presence of
multiple bonds
FUNCTIONALIZED HYDROCARBONS
The term functional group derives from the
functionality or chemical character that a
specific atom or group of atoms imparts to
an organic compound.
Even a carbon–carbon double or triple bond can
justifiably be called a “functional group.”
A group of organic compounds with the
same functional group forms a family.
OPTIONAL PROBLEMS FOR EXTRA PRACTICE
60. c & d 83. a & c
61. a & b 86, b & c
62. a & b 88
64. b & c 90
66. a & b 94
68. b & c 98
72. a & b 100 108
74 102 110
78 104
82 c & d 106
top related