atoms, elements, molecules and compounds
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Copyright 2011 Pearson Education, Inc.Tro: Chemistry: A Molecular Approach, 2/e
Topic 1:
Atoms,Elements,
Molecules andCompounds
Ms. Amira Raihana Adnan
Chemistry Unit, CFGS,
Universiti Tenaga Nasional (UNITEN).
1
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Law of Conservation of Mass
2
Antoine Lavoisier
1743-1794
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Total mass of the materialsyou have before thereaction must equal the
total mass of the materialsyou have at the endtotal mass of reactants =
total mass of products
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Reaction of Sodium with Chlorine to
Make Sodium Chloride
3
7.7 g Na + 11.9 g Cl2 19.6 g NaCl
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4
Daltons Atomic Theory
Law of Multiple Proportions
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Daltons Atomic Theory
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1. Each element is composed of tiny, indestructibleparticles called atoms
2. All atoms of a given element have the samemass and other properties that distinguish themfrom atoms of other elements
3. Atoms combine in simple, whole-number ratios
to form molecules ofcompounds
4. In a chemical reaction, atoms of one elementcannot change into atoms of another element
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Practice Decide if each statement is correct
according to Daltons model of the atom
Copper atoms can combine with zinc atoms tomake gold atoms
Water is composed of many identicalmolecules that have one oxygen atom and two
hydrogen atoms
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J.J. Thomson
Measured the mass and charge of electronusing cathode ray tube
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Millikans Oil Drop Experiment
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Measured mass of electron
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Electrons
Electrons are tiny, negatively chargedparticles found in all atoms
The electron has a charge of1.60 x 1019 C
The electron has a mass of 9.1 x 1028 g
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Thomsons Plum Pudding Atom
The structure of the atom containsmany negatively charged electrons
These electrons are held in theatom by their attraction for a
positively charged electric fieldwithin the atom
The mass of the atom is due to themass of the electrons within it
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Predictions of the
Plum Pudding Atom
The mass of the atom is due to the mass ofthe electrons within it
electrons are the only particles in Plum Pudding
atoms, therefore the only source of mass
The atom is mostly empty spaceshould not have a bunch of negatively charged
particles near each other as they would repel
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Rutherfords Interpretation
the Nuclear Model
1. The atom contains a tiny dense center calledthe nucleus
2. The nucleus has essentially the entire mass of
the atom
3. The nucleus is positively charged
4. The electrons are dispersed in the empty spaceof the atom surrounding the nucleus
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Structure of the Nucleus Rutherford proposed that the nucleus
had a particle that had the sameamount of charge as an electron butopposite sign these particles arecalled protons
based on measurements of the nuclearcharge of the elements
protons are subatomic particles foundin the nucleus with a charge = +1.60 x
1019
C and a mass = 1.67262 x 1024
g Because protons and electrons have
the same amount of charge, for the atomto be neutral there must be equal
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Neutron
Neutrons are subatomic particles with a mass= 1.67493 x 1024 g and no charge, and are
found in the nucleus
1 amu
slightly heavier than a proton
no charge
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Elements
Each element has a unique number of protonsin its nucleus
The number of protons in the nucleus of anatom is called the atomic numberthe elements are arranged on the Periodic Table in
order of their atomic numbers
Each element has a unique name and symbolsymbol either one or two letters
one capital letter or one capital letter and one
lowercase letter
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Isotopes
Element have the same number of protons butdifferent masses and numbers of neutrons
Identified by theirmass numbers
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Neon
9.25%221210Ne-22 or
0.27%211110Ne-21 or
90.48%201010Ne-20 or
Percent
Natural
Abundance
A, Mass
Number
Number of
Neutrons
Number of
ProtonsSymbol
Ne2010
Ne2110
Ne2210
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E l 2 3b H t l t
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Example 2.3b: How many protons, electrons,
and neutrons are in an atom of ?
for most stable isotopes, n0 p+Check:
Z = 24 = # p+
# e = # p+ = 24
Solution:
in neutral atom, # p+ = # e-
mass number = # p+ + # n0
Conceptual
Plan:
Relationships:
therefore A = 52, Z = 24
# p+, # e, # n0
Given:
Find:
Cr5224
symbol atomic
number# p+ # e
symbol atomic & mass
numbers
# n0
A = Z + # n0
52 = 24 + # n0
28 = # n0
21
Cr5224
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Charged Atoms
When atoms gain or lose electrons, theyacquire a charge
Charged atoms or groups of atoms arecalled ions
When atoms gain electrons, they becomenegatively charged ions, called anions
When atoms lose electrons, they becomepositively charged ions, called cations
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Ions and Compounds
Ions behave much differently than theneutral atoms
e.g., the metal sodium, made of neutral Na
atoms, is highly reactive and quite unstable;
however, the sodium cations, Na+, found in table
salt are very nonreactive and stable
Because materials such as table salt areneutral, there must be equal amounts ofcharge from cations and anions in them
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Atomic Structures of Ions
Nonmetals form anions For each negative charge, the ion has
one more electron than the neutral atom
F = 9 p+ and 9 e, F = 9 p+ and 10 e
P = 15 p+ and 15 e, P3 = 15 p+ and 18e
Anions are named by changing theending of the name to - ide
fluorine F + 1e F fluoride ionoxygen O + 2e O2 oxide ion
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Atomic Structures of Ions
Metals form cations For each positive charge, the ion has one less
electron than the neutral atom
Na atom = 11 p+ and 11 e, Na+ ion = 11 p+ and 10 eCa atom = 20 p+ and 20 e, Ca2+ ion = 20 p+ and 18e
Cations are named the same as the metal
sodium Na
Na+
+ 1e
sodium ioncalcium Ca Ca2+ + 2e calcium ion
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Practice Complete the table
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3Al
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Practice Complete the table
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2Mg
2S
Br
3Al
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About of the elements are classified as metals.
They have a reflective surface, conduct heat andelectricity better than other elements, and are
malleable and ductile
Most of the remaining elements are classified as
nonmetals. Their solids have a non-reflectivesurface, do not conduct heat and electricity well,
and are brittle.
A few elements are classified as metalloids.
Their solids have some characteristics of metalsand some of nonmetals.
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The Modern Periodic Table
Elements with similar chemical andphysical properties are in the same column
Columns are called Groups orFamiliesdesignated by a number and letter at top
Rows are called Periods
Each period shows the pattern ofproperties repeated in the next period
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Practice What is the charge on each of
the following ions?
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potassium cation
sulfide anion
calcium cation bromide anion
aluminum cation
K+
S2
Ca2+
Br
Al
3+
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Mass Spectrometry
Masses and abundances of isotopes are measured with amass spectrometer
Atoms or molecules are ionized, then accelerated down atube
some molecules are broken into fragments during the ionizationprocess
these fragments can be used to help determine the structure of the
molecule
Their path is bent by a magnetic field, separating them bymass
similar to Thomsons cathode ray experiment
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Mass Spectrometer
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Mass Spectrum
A mass spectrum is agraph that gives therelative mass and relativeabundance of each
particle Relative mass of the
particle is plotted in thex-axis
Relative abundance of theparticle is plotted in the y-axis
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Example 2.5: If copper is 69.17% Cu-63 with a mass of 62.9396
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Example 2.5: If copper is 69.17% Cu 63 with a mass of 62.9396amu and the rest Cu-65 with a mass of 64.9278 amu, find
coppers atomic mass
the average is between the two masses,
closer to the major isotope
Check:
Solution:
Conceptual
Plan:
Relationships:
Cu-63 = 69.17%, 62.9396 amu
Cu-65 = 100-69.17%, 64.9278 amuatomic mass, amu
Given:
Find:
isotope masses,
isotope fractionsavg. atomic mass
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Practice Ga 69 with mass 68 9256 amu and
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PracticeGa-69 with mass 68.9256 amu and
abundance of 60.11% and Ga-71 with mass 70.9247
amu and abundance of 39.89%. Calculate the
atomic mass of gallium.
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Chemical Bonds
Chemical bonds are forces of attractionbetween atoms
The bonding attraction comes fromattractions between protons and electrons
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Bond Types Two general types: ionic and covalent
Ionic bondsresult when electrons have beentransferred between atoms, resulting in oppositelycharged ions that attract each othergenerally found when metal atoms bond to nonmetal
atoms Covalent bondsresult when two atoms share
some of their electronsgenerally found when nonmetal atoms bond together
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Chemical Formula
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To represent the compounds
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Types of Formula:
Empirical Formula
An empirical formulagives the relative numberof atoms of each elementin a compound
The empirical formula for the ionic compound fluorspar is CaCl2.
This means that there is 1 Ca
2+
ion for every 2 Cl
ions in thecompound.
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Types of Formula:
Molecular Formula
Amolecular formulagives the actual numberof atoms of each element in a molecule of a
compound
The molecular formula is C2H2O4. This does not tell you that the
carbon atoms are attached together in the center of the molecule,
and that each is attached to two oxygen atoms.
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Types of Formula:
Structural Formula
A structural formulauses lines to representcovalent bonds and shows how atoms in a
molecule are connected or bonded to each other
single line = two shared electrons, a single covalent bond
double line = four shared electrons, a double covalent bond
triple line = six shared electrons, a triple covalent bond
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Structural Formula of Oxalic Acid
O C
O
C
O
O HH
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Representing Compounds:
Molecular Models
Models show the 3-dimensional structurealong with all the other information given in the
structural formula
Ball-and-stick models use balls to representthe atoms and sticks to represent the
attachments between them
Space-filling models use interconnectedspheres to show the electron clouds of atoms
connecting together
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Models of Oxalic Acid
Ball and stickSpace filling
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Classifying Elements & Compounds
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Atomic elements = elements whose particles aresingle atoms
Molecular elements = elements whose particlesare multi-atom molecules
Molecular compounds = compounds whoseparticles are molecules made of only nonmetals
Ionic compounds = compounds whose particlesare cations and anions
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Classify Each of the Following as Either an
Atomic Element, Molecular Element,
Molecular Compound, or Ionic Compound
Aluminum, Al
Aluminum chloride, AlCl3Chlorine, Cl2
Acetone, C3H6O
Carbon monoxide, COCobalt, Co
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atomic element
ionic compoundmolecular element
molecular compound
molecular compoundatomic element
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Ionic Compounds
Compounds of metals with nonmetals aremade of ions
Have a 3-dimensional array of cations andanions made offormula units
Many contain polyatomic ionsseveral atoms attached together by covalent
bonds into one ion
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E l 3 3 W i h f l f d
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Example 3.3: Write the formula of a compound
made from aluminum ions and oxide ions
1. Write the symbol for themetal cation and its charge
2. Write the symbol for thenonmetal anion and its
charge3. Charge (without sign)becomes subscript for other
ion
4. Reduce subscripts tosmallest whole number ratio
5. Check that the total chargeof the cations cancels the
total charge of the anions
Al3+ column 3A
O2 column 6A
Al+3 O2
Al2O3
Al = (2)(+3) = +6
O = (3)(2) = 6
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Practice What are the formulas for
compounds made from the following ions?
Potassium ion with a nitride ion
Calcium ion with a bromide ion
Aluminum ion with a sulfide ion
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Practice What are the formulas for
compounds made from the following ions?
K+ with N3 K3N
Ca2+ with Br CaBr2
Al3+
with S2
Al2S3
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Naming Metal Cations
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Metals with variable
Chargesmetals whose ions
can have more than
one possible charge
Naming Metal Cations
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Naming Metal Cations
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Metals with invariant chargemetals whose ions can only
have one possible charge
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Naming Monatomic Nonmetal Anion
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To name anion, change ending on the elementname toide
1. KCl
2. MgBr2
3. Al2S3
potassium chloride
magnesium bromide
aluminum sulfide
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Practice Find the charge on the cation
1. TiCl4
2. CrO3
3. Fe3N2
4 Cl = 4, Ti = 4+
3 O = 6, Cr = 6+
2 N = 6, 3 Fe = 6+, Fe = 2+
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Example: Naming binary ionic
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p g y
with variable charge metal
CuF2
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1. Identify cation and anion
F = F because it is Group 7
Cu = Cu2+ to balance the two () charges from 2 F
2. Name the cationCu2+ = copper(II)
3. Name the anion
F = fluoride
4. Write the cation name first, then the anion name
copper(II) fluoride
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Name the following compounds
1. TiCl4
2. PbBr2
3. Fe2S3
titanium(IV) chloride
lead(II) bromide
iron(III) sulfide
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Practice What are the formulas for
compounds made from the following ions?
copper(II) ion with a nitride ion
iron(III) ion with a bromide ion
Cu
2+
with N
3
Cu3N2
Fe3+ with Br FeBr3
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Compounds Containing Polyatomic Ions
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Polyatomic ions are single ions that containmore than one atom
Often identified by parentheses around ion informula
Name and charge of polyatomic ion do not change
Name any ionic compound by naming cation firstand then anion
P i di P tt f P l t i I
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Periodic Pattern of Polyatomic Ions
-ate groups
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Name the Following Compounds
1. NH4Cl
2. Ca(C2H3O2)2
3. Cu(NO3)2
ammonium chloride
calcium acetate
copper(II) nitrate
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Example Writing formula for ionic
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Example Writing formula for ionic
compounds containing polyatomic ion
Iron(III) phosphate
1. Write the symbol for the
cation and its charge
2. Write the symbol for the
anion and its charge
3. Charge (without sign)
becomes subscript for other
ion
4. Reduce subscripts to
smallest whole number ratio
5. Check that the total charge
of the cations cancels the
total charge of the anions
Fe3+
PO43
Fe3+ PO43 Fe3(PO4)3
Fe = (1)(3+) = +3
PO4= (1)(3) = 3
FePO4
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Practice What are the formulas for
compounds made from the following ions?
aluminum ion with a sulfate ion
chromium(II) with hydrogen carbonate
Al3+ with SO42 Al2(SO4)3
Cr2+ with HCO3 Cr(HCO3)2
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Hydrates are ionic compounds containing a
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specific number of watersfor each formula unit
CoCl2
6H2
O = cobalt (II) chloride hexahydrate
CaSO4H2O = calcium sulfate hemihydrate
MgSO47H2O = magnesium sulfate heptahydrate
NiCl26H2O = nickel (II) chloride hexahydrate
Example: Naming binary molecular
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Example: Naming binary molecular
BF3
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1. Name the first element
boron
2. Name the second element with anide
fluorine
fluoride3. Add a prefix to each name to indicate the subscript
monoboron, trifluoride
4. Write the first element with prefix, then the second
element with prefixa) drop prefix monofrom first element
boron trifluoride
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Name the Following
NO2
PCl5
I2F7
nitrogen dioxide
phosphorus pentachloride
diiodine heptafluoride
68Tro: Chemistry: A Molecular Approach, 2/e
E l Bi M l l
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Example: Binary Molecular
dinitrogen pentoxide
69Tro: Chemistry: A Molecular Approach, 2/e
Identify the symbols of the elements
nitrogen = N
oxide = oxygen = O Write the formula using prefix number for subscript
di = 2, penta = 5
N2O5
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Write Formulas for the Following
dinitrogen tetroxide
sulfur hexafluoride
diarsenic trisulfide
N2O4
SF6
As2S3
70Tro: Chemistry: A Molecular Approach, 2/e
Example: Naming binary acids
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Example: Naming binary acids
HCl(aq)
71Tro: Chemistry: A Molecular Approach, 2/e
1. Identify the anion
Cl = Cl, chloride because Group 7A
2. Name the anion with anicsuffix
Cl = chloride chloric
3. Add a hydro-prefix to the anion name
hydrochloric
4. Add the word acidto the endhydrochloric acid
E l N i id
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Example: Naming oxyacids
H2SO4(aq)
72Tro: Chemistry: A Molecular Approach, 2/e
1. Identify the anion
SO4 = SO42 = sulfate
2. If the anion hasatesuffix, change it toic. If the
anion hasi tesuffix, change it to -ousSO4
2 = sulfate sulfuric
3. Write the name of the anion followed by the wordacid
sulfuric acid
(kind of an exception, to make it sound nicer!)
Example: Naming oxyacids
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Example: Naming oxyacids
H2SO3(aq)
73Tro: Chemistry: A Molecular Approach, 2/e
1. Identify the anion
SO3 = SO32 = sulfite
2. If the anion hasatesuffix, change it toic. If the
anion hasi tesuffix, change it to -ousSO3
2 = sulfite sulfurous
3. Write the name of the anion followed by the wordacid
sulfurous acid
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Name the Following
H2S
HClO3
HNO2
hydrosulfuric acid
chloric acid
nitrous acid
74Tro: Chemistry: A Molecular Approach, 2/e
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Writing Formulas for Acids
When name ends in acid, formulas starts with H
Write formulas as if ionic, even though it ismolecular
Hydro prefix means it is binary acid, no prefixmeans it is an oxyacid
For oxyacid, if ending is ic, polyatomic ion
ends in
ate; if ending is
ous, polyatomic ionends in ous
75Tro: Chemistry: A Molecular Approach, 2/e
Example: Oxyacids
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Example: Oxyacids
sulfurous acid
1. Write the symbol for thecation and its charge
2. Write the symbol for the
anion and its charge
3. Charge (without sign)becomes subscript for other
ion
4. Add (aq) to indicate
dissolved in water
5. Check that the total charge
of the cations cancels the
total charge of the anions
H+
SO32
H+ SO32 H2SO3
H = (2)(1+) = +2
SO3= (1)(2) = 2
H2SO3(aq)
in all acids thecation is H+
no hydro means
polyatomicion
-ous means -ite ion
76Tro: Chemistry: A Molecular Approach, 2/e
P ti Wh t th f l f th
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Practice What are the formulas for the
following acids?
H+ with ClO2 HClO2
H+ with PO43 H3PO4
H+ with Br HBr
chlorous acid
phosphoric acid
hydrobromic acid