Chapter 2
Atoms, Molecules, and Ions
1
Atoms and Atomic Structure
•
Dalton’s Atomic Theory - 1808
1. -Elements are composed of small, nondivisible
2.
3.
4.
5.
6.
particles called atoms
-Atoms of an element have identical properties
and differ from those of other elements
-Atoms cannot be created, destroyed, or
transformed into other atoms
-Compounds are formed when atoms of different
elements combine in whole-number ratios
-Atom ratios are constant in a given compound
-Chemical reactions rearrange and recombine 2
atoms but do not destroy them
Structure of the Atom
1. -atom is mostly empty space
2. -consists of a very small, dense center called the
nucleus
3. -nearly all of the atom’s mass is in the nucleus
4. -the nuclear diameter is 1/10,000 to 1/100,000
times less than the atom’s radius
3
Structure of the Atom
• -Sir John Joseph Thompson and Ernest
Rutherford established a model of the
atom still in use today
• -Three fundamental particles make-up
atoms:
Particle
Mass (amu) Charge
Electron (e-)
0.00054858
-1
Proton (p,p )
1.0073
+1
Neutron(n,n0)
1.0087
0
+
4
5
Elements
• substances that cannot be decomposed
into simpler substances via chemical
reactions
• Elemental symbols-abbreviation representing
each element on periodic table
– -First letter capital, second letter lower case
– ie: C, Ca, Co
– CO is not an element (it’s a compound)
because there are two capital letters
6
The Periodic Table
• 1869 - Mendeleev & Meyer
– Discovered the periodic law
• -Organized based on related chemical
reactivities, physical properties, other behaviors
and trends
• -The properties of the elements are periodic
functions of their atomic numbers (not atomic
masses)
Law of Chemical Periodicity
7
The Periodic Table
• Groups or families
– Vertical group of elements on periodic table
– Similar chemical and physical properties
•Period
–Horizontal group of elements on periodic table
–Transitions from metals to nonmetals
•Three regions
–Metals, nonmetals and metalloids
8
• Period
– Horizontal group of elements on the
periodic table
• -Transition from metals to nonmetals
9
• Groups (families)
– Vertical group of elements on the
periodic table
• -similar chemical and physical properties
10
• Metalloids
• separate metals from nonmetals
• Metals are to the left of stair
step
– -Approximately 80% of the
elements
• Nonmetals are to the right of
stair step
– -Approximately 20% of the
elements
• Elements box on the stair step
have properties between
metals and nonmetals
11
The Periodic Table
•
Chemical properties of metals
1.
2.
3.
4.
-Outer (valence) shells contain few electrons
-Form cations by losing electrons
-Form ionic compounds with nonmetals
-Solid state characterized by metallic bonding
-Conductors of electricity and heat
-Malleable: can be hammered
-Ductile: drawn into wire
-Typically solids (except mercury)
12
The Periodic Table
• Chemical properties of nonmetals
1. -Outer shells contain four or more electrons
2. -Form anions by gaining electrons (- charge)
3. -Form ionic compounds with metals and
covalent compounds with other nonmetals
4. -Form covalently bound molecules; noble
gases are monatomic and have full electron
shells
5. -Insulators meaning poor conductors
6. -Typically gasses or solids (Br2 liquid I2 solid)
13
The Periodic Table:
• Periodic trends
Atomic number increase
More
AtomicMetallic
number
increase
Size increases
More
Metallic
Size decreases
Periodic
Periodic Table
Chart
Form compounds
with similar formulas
14
Metals
• Group IA metals:
– Alkali metals- Li, Na, K, Rb, Cs, Fr
– -solids, reactive, and never found in nature as free elements
– -chemical formula from top-to-bottom are the same
• Group IIA metals:
– Alkaline earth metals- Be, Mg, Ca, Sr, Ba, Ra
– -solids, reactive, and mostly found in nature as compounds
– -chemical formula from top-to-bottom are the same
15
Metals
Group IIIA: B, Al, Ga, In, Tl
• -Aluminum (Al) most abundant metal in the earth’s crust
• -Boron (B) is the only nonmetal
• -forms compounds of analogous chemical formulas
Group IVA: C, Si, Ge, Sn, Pb
-most variation in their properties
-Carbon (C) is the “element of life”
CO2
carbonate-limestone, coral, shells
fossil fuels-coal, petroleum, natural gas
-Silicon (Si) is found as gemstones, glass, and sand
-Lead (Pb) was used as water pipes, paint, and in gasoline
-form compounds of analogous chemical formulas
16
Allotropes
• elements (nonmetals) that exist in
several different and distinct forms each
having its own properties
17
Group VA: N, P, As, Sb, Bi
• Nitrogen (N)
• -makes up ~75% of the earth’s atmosphere
• -used to make fertilizer (NH3)
• -found in biological systems in proteins and DNA
• Phosphorous (P)
• -has several allotropes most common are white
and red phosphorus
• -white ignites spontaneously in air and used to
make phosphoric acid
• -red phosphorus is used in striking strips of
matchbooks
18
• -form similar types of chemical compounds
• Group VIA: nonmetals
– Chalcogens
– O, S, Se, Te
-Oxygen (O) is the power source of life on earth by
combining with other substances, and has allotropes
-Sulfur (S) (and even Selenium, Se) is fowl smelling, and S
appears as allotropes
-these elements are considered poisonous, but essential for
human diets
-Some variations is chemistries, but form analogous
formulas
19
• Group VIIA nonmetals
– halogens
– F, Cl, Br, I
-All exist in the form of diatomic molecules
-At room temperature, Fluorine (F) and Chlorine (Cl) are
gases where Bromine (Br) is a liquid and Iodine (I) is a
solid
-Some of the most reactive of all elements they react
with metals and nonmetals to form compounds
20
• Group VIIIA nonmetals
– noble, inert or rare gases
– He, Ne, Ar, Kr, Xe, Rn
-least reactive elements and for a long time considered
unreactive
-all are gases and none are abundant on earth
-He is the second most abundant element in the universe
21
Transition Metals
• Most are found as compounds in nature
– -Ag, Au, Pt are less reactive and can be
found as pure substances
– -These elements are commercially useful as
building materials, in paints, catalytic
converters, coins, batteries, and fireworks
– -Play important roles in biological
processes
– -Bottom two rows of the periodic table are
used in television picture tubes, atomic
fuel, smoke detectors
22
23
Atomic Number (Z)
the number of protons in the nucleus
• -numbered consecutively on the periodic table
• atomic number determines the element:
• -elements differ from one another by the number
of protons in the nucleus
• -the number of electrons in a neutral atom (no
charge) is equal to the atomic number
• -negatively charged species have more electrons
• -positively charged species have less electrons
24
Mass Number (A)
• sum of the number of protons and neutrons
– Z = atomic number (number of protons)
– N = number of neutrons
–A=Z+N
• One common symbolism used to show mass
and proton numbers is:
A
Z
E for example
12
6
48
20
C, Ca,
197
79
14
?
63
?
18
8
Au
N, Cu, ?
25
Mass Number (A)
• How many protons and neutrons are in the
following?
16
23

Na
8
11
O
18
8
40
20
2
238
92
82
35

O
U
236
92
U
Ca
32
16
Br
S
2
26
Mass Number (A)
Give the number of protons, neutrons and
electrons and the correct element symbol:
24
12
?
200
79
15
7
?
?
27
Isotopes
• Atoms of the same element but with different
numbers of neutrons (or same atomic number,
but different mass numbers)
Isotopes have different masses and mass number(A)
values but are the same element
• Example: hydrogen isotopes
1
or protium is the most common hydrogen isotope
1
• -one proton and no neutrons
or deuterium (D) is the second most abundant hydrogen
2
isotope
1
• -one proton and one neutron
3
or tritium (T) is a radioactive hydrogen isotope
28
1
• -one proton and two neutrons
H
H
H
Atomic Weights
• How do we know what the
values of these atomic
weights are?
29
Atomic Weight
• the weighted average of the masses of the
elements stable isotopes
• Example: Naturally occurring Cu consists of
2 isotopes. It is 69.1% 63Cu with a mass of
62.9 amu, and 30.9% 65Cu, which has a mass
of 64.9 amu. Calculate the atomic weight of
Cu to one decimal place.
30
Atomic Mass
• weighted average of the masses of an
elements stable isotopes as listed on
the periodic table
– For example: hydrogen (H) = 1.008 amu
–
calcium (Ca) = 40.078 amu
31
Molecules
smallest unit of a pure substance that can be
divided and still retain the composition and
chemical properties of the substance
Examples of molecules:
–
–
–
–
–
–
H2
O2
S8
H2O
CH4
C2H6O
Molecular formulas: describe the composition of32
substances, but provide no structural information
Classes of Substances:
monatomic elements
He, Au, Na
diatomic elements (binary molecules)
O2, H2, Cl2, F2, I2, N2,Br2
complex elements
O3, S4, P8
Compounds (molecules)
H2O, C12H22O11
33
Molecular (Chemical) Formulas
Compound
HCl
H2O
NH3
C3H8
Contains
34
Chemical bonds
Attractive forces that hold atoms together in
compounds
Chemical bond types:
1.
Ionic bonding: resulting from electrostatic attractions
between ions
-formed by the transfer of one or more electrons from
one atom to another
-attraction of cations for anions typically form solids
-most often formed by interactions between metals
and nonmetals
2.
Covalent bonding: results from sharing one or more
electron pairs between two atoms
- typically formed by interactions between nonmetals35
and nonmetals
Ionic Compounds
An ion is an atom or a group of atoms
possessing a net electrical charge
positive (+) ions or cations
These atoms have lost 1 or more electrons
Metals lose electrons to form cations (monoatomic cations)
Consider Group IA and IIA metals
negative (-) ions or anions
These atoms have gained 1 or more electrons.
Nonmetals gain electrons to form anions (monoatomic
anions)
Consider the nonmetals-groups IVA through VIIA
36
Ionic Compounds
• Coulomb’s Law: dictates the strength of
ionic bonds – it is an inverse square law

q q 
F
= k

d
where

2
F  force of attraction between ions
q  magnitude of charge on ions
d  distance between center of ions
37
Ionic Compounds
Cations:
Na+, Ca2+, Al3+ (monoatomic cations)
NH4+ (polyatomic cation)
Anions:
F-, O2-, N3- (monoatomic anions)
SO42-, PO43-, HCO3- (polyatomic anions)
Transition metals forming cations
No pattern exists for determining the charge
Many metals form several different ions (charge
states)
H and noble gases are special cases
38
Ionic Formulas
Formulas of ionic compounds are
determined by the charges of the ions
-total charge of the cations must equal the
total charge of the anions
-The compound must be neutral
NaCl
KOH
CaSO4
Al(OH)3
sodium chloride
(Na1+ & Cl1-)
potassium hydroxide (K1+ & OH1-)
calcium sulfate
(Ca2+ & SO42-)
aluminum hydroxide (Al3+ & OH1-)
39
Writing binary chemical formulas
Charge becomes subscript. Then give the
subscript as lowest common denominator
Li1
Cl 
LiCl
Ca 2 F 
CaF2
Al 3 Br 
AlBr3
Mg 2 O 2
Mg 2O2  MgO
Ba 2
Ba 3 N 2
K

Cu2
N 3
Cl

I
Fe3 O 2
??
??
??
40
Naming Ionic Compounds
metal cation and a nonmetal anion
1. Name the cation
2. Name the anion, nonmetal stem with –ide
ending
LiBr
Li2S
Al2O3
lithium bromide
magnesium chloride
lithium sulfide
You do it!
41
Naming Ionic Compounds
LiBr
MgCl2
Li2S
Al2O3
Na3P
Mg3N2
lithium bromide
magnesium chloride
lithium sulfide
aluminum oxide
Notice that binary ionic compounds with
metals having one oxidation state
They do not use prefixes or Roman
numerals!!!
42
Naming Cations
Monoatomic cations
use the name of the metal plus the word “cation”
Examples: Al3+, Li+, Ca2+
Transition metals that have multiple charges:
Two methods are used
1. Older method:
-add suffix “ic” to element’s Latin name for higher oxidation
state (higher positive charge)
-add suffix “ous” to element’s Latin name for lower
oxidation state (lower positive charge)
2. Modern method:
use Roman numerals in parentheses to indicate metal’s43
oxidation state
Naming Ionic Compounds
ionic compounds containing metals with
more than one oxidation state (charge)
memorize them on your handout
Metals exhibiting multiple oxidation states
are:
1. most of the transition metals
2. metals in groups IIIA (except Al), IVA, & VA
on the periodic table
44
Naming Ionic Compounds
Compound
Old System
FeBr2
ferrous bromide
ferric bromide
SnO
SnO2
CoCl2
CoCl3
cobaltous chloride
cobaltic chloride
plumbous sulfide
plumbic sulfide
Modern System
iron(II) bromide
iron(III) bromide
tin(II) oxide
tin(IV) oxide
lead(II) sulfide
lead(IV) sulfide
45
Naming Ionic Compounds
There are polyatomic ions that form binary
ionic compounds
1. OH- hydroxide
2. CN- cyanide
3. NH4+ ammonium
KOH
Al(OH)3
Fe(OH)2
potassium hydroxide
barium hydroxide
aluminum hydroxide
You do it!
46
Naming Ionic Compounds
KOH
Ba(OH)2
Al(OH)3
Fe(OH)2
potassium hydroxide
barium hydroxide
aluminum hydroxide
iron (II) hydroxide
iron (III) hydroxide
Ba(CN)2
ammonium sulfide
NH4CN
47
Naming Anions
Monoatomic anions
use the name of the nonmetal plus the word “-ide” at the end
Examples: F-, Cl-, S2-
Polyatomic anions
Some guidelines for oxoanions (contain Oxygen)
• If only 2 similar formula type anions exist, the one containing the
greater number of oxygen atoms have an “–ate” ending, and the
smaller number of oxygen atoms have an “-ite” ending
NO3NO2SO42SO32• If more than two exist, the one with the largest number of oxygen
atoms have a prefix “per-” and an “-ate” ending, and the smallest
number of oxygen atoms have a prefix “hypo-” and an “-ite” ending
ClO4ClO3ClO2ClO• Oxoanions containing H are named with the word hydrogen in front,
if more than one H is contained in the oxoanion, then prefixes are
used to indicate the number of hydrogen atoms
48
HPO42H2PO4-
Naming Ionic Compounds
On Your Own
NaNO2
Na2SO3
Na3PO4
MgSO4
Ca(NO3)2
BaCO3
sodium nitrite
sodium nitrate
sodium sulfate
potassium phosphate
49
Ionic Formulas
What is the name of K2SO3?
Potassium sulfite
What is charge on sulfite ion?
-2
What is the formula of ammonium sulfide?
(NH4)2S
What is charge on ammonium ion?
+1
What is the formula of aluminum sulfate?
Al2(SO4)3
What is charge on both ions?
+3
-2
50
Name or Write the formula:
Formula
1. Cu(OH)2
2. CuOH
3. MgCl2
4. Li2O
5. Zn3N2
6.
7.
8.
9.
10.
Name
calcium bromide
sodium hydroxide
aluminum phosphide
barium iodide
magnesium cyanide
51
Name or Write the formula:
Formula
1.
2.
3.
4.
Name
iron(II) bromide
iron(III) hydroxide
copper(II) oxide
lead(IV) cyanide
52
Commonly Found Ionic Compounds
53
Covalent Compounds
Covalent Bonds: Sharing of one or
more electron pairs between atoms
Representation of the formation of
a H2 molecule from 2 H atoms
54
Naming Molecular (Covalent)
Compounds
molecular formulas for these compounds are
generally written with increasing group number
–
–
Use the first nonmetal’s name with the appropriate prefix
di-, tri-, tetra-, etc (excluding mono-)
Followed by the next nonmetal: use this nonmetal’s stem
with “-ide” ending and the appropriate prefix mono-, di-,
tri-, etc
Exception: hydrogen
– write the word hydrogen
– then the following nonmetal: use the nonmetal stem with
55
the “-ide” ending
Naming Nonmetals
Element
Boron (B)
Carbon (C)
Silicon (Si)
Nitrogen (N)
Fluorine (F)
Chlorine (Cl)
Stem
bor
carb
silic
nitr
fluor
chlor
56
Naming Nonmetals
Element
Bromine (Br)
Iodine (I)
Oxygen (O)
Sulfur (S)
Selenium (Se)
Phosphorus (P)
Hydrogen (H)
Stem
brom
iod
ox
sulf
selen
phosph
hydr
57
Naming Molecular Compounds
58
Naming Covalent Compounds
Formula
HF
HCl
HBr
H2S
Name
hydrogen fluoride (hydrofluoric acid)
hydrogen chloride (hydrochloric acid)
hydrogen bromide (hydrobromic acid)
You do it!
59
Names and Formulas
• What is the formula of nitric acid?
• What is the formula of sulfur trioxide?
60
Naming Covalent Compounds
Formula
CO
_____
SO3
Name
____________
carbon dioxide
oxygen difluoride
P4O6
tetraphosphorus decoxide
61
Naming Covalent Compounds
Formula
N 2O
NO
N2O3
NO2
Modern Name
dinitrogen monoxide
nitrogen monoxide
dinitrogen tetroxide
dinitrogen pentoxide
62
63
Describing Compound Formulas
% composition = mass of an individual
element in a compound divided by the total
mass of the compound x 100
% comp =
component mass
total mass
x 100
64
Percent Composition
What is the percent composition of H in
C3H8?
65
Percent Composition
What is the percent composition of H in
H2O?
66
Ans: 11.21%
Percent Composition
Calculate the percent composition of each
component in Fe2(SO4)3 to 3 sig. fig.
On your own
27.9% Fe
24.1% S
48.0% O
67
Total = 100%
Empirical and Molecular Formulas
Empirical Formula:
smallest whole-number ratio of atoms present in a
compound
Molecular Formula:
actual numbers of atoms of each element present
in a molecule of the compound
We determine the empirical and molecular
formulas of a compound from the percent
68
composition
Empirical And Molecular Formulas
69
Empirical Formulas
A compound contains 24.74% K, 34.76%
Mn, and 40.50% O by mass. What is
its empirical formula?
Make the simplifying assumption that we
have 100.0 g of compound
In 100.0 g of compound there are:
24.74 g of K
34.76 g of Mn
40.50 g of O
70
Empirical Formulas
A sample of a compound contains 6.541g
of Co and 2.368g of O. What is
empirical formula for this compound?
You do it!
71
Molecular Formulas
A compound is found to contain 85.63% C
and 14.37% H by mass. In another
experiment its molar mass is found to be
56.1 g/mol. What is its molecular
formula?
72
More Practice
What mass of ammonium phosphate,
(NH4)3PO4, would contain 15.0 g of N?
MW = 149.08626 g/mol
73
The Mole
• an amount of a substance that contains
as many elemental entities as there are
atoms in exactly 12.000g of carbon-12
isotope
– -This number is an amount of atoms, ions,
or molecules that is large enough to see
and easier to handle
– -A mole (mol) = some number of things
• Just like a dozen = 12 things
• One mole = 6.022 x 1023 things
– -Avogadro’s number (NA) = 6.022 x 1023
74
The Mole
• Molar mass: mass in grams that is equal to the
atomic weight of the element (in grams)
• H has an atomic weight of 1.00794 g
1.00794 g of H atoms = 6.022 x 1023 H atoms (= 1 mol)
• Mg has an atomic weight of 24.3050 g
24.3050 g of Mg atoms = 6.022 x 1023 Mg atoms (= 1 mol)
75
The Mole
76
The Mole
77
The Mole
• Calculate the mass of a single Mg atom,
in grams, to 3 significant figures.
78
The Mole
• Calculate the number of atoms in onemillionth of a gram of Mg to 3
significant figures.
79
The Mole
• How many atoms are contained in 1.67
moles of Mg?
80
The Mole
• How many moles of Mg atoms are present in
73.4 g of Mg?
YOU MUST KNOW
HOW TO DO THESE PROBLEMS
81
Molecular Weights
Add atomic weights of each atom in
the molecule
molar mass (molecular weight) of propane
(C3H8):
3  C  3  12.01 amu  36.03 amu
8  H  8  1.01 amu  8.08 amu
Molar mass
 44.11 amu
82
Molecular Weights
molar mass of calcium nitrate, Ca(NO3)2:
83
Formula Weights, Molecular Weights,
and Moles
One Mole of:
Cl2 = 70.90g
C3H8 = 44.11 g
Contains
6.022 x 1023 Cl2 molecules
2(6.022 x 1023 ) Cl atoms
= 1.204 x 1024 Cl atoms
6.022 x 1023 C3H8 molecules
3 (6.022 x 1023 ) C atoms
8 (6.022 x 1023 ) H atoms
84
Formula Weights, Molecular Weights,
and Moles
Calculate the number of C3H8 molecules in
74.6 g of propane:
85
Formula Weights, Molecular Weights,
and Moles
Calculate the number of O atoms in 26.5
g of Li2CO3:
86