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Chapter Two:
Atoms, Molecules & Ions

Atomic Theory & Structure

Isotopes, Numbers & Masses

Periodic Table

Molecules, Ions, Compounds & Formulas

Naming Species
Atomic Theory and Structure
What is the smallest piece of matter possible?

Democritus called the smallest particles “atomos”

Dalton’s atomic theory of matter:

-elements are composed of small particles -- atoms
-all atoms of an element are identical
-atoms are not created or destroyed chemically
-compounds formed by chemical combination of two
or more elements
-a given compound has same relative number &
type of atoms (law of constant composition)
-atoms retain character during chemical rxns. only
undergo rearrangement (conservation of matter)
Law of Multiple Proportions
If two elements, A & B, form more than one compound,
the masses of B that can combine with a given mass of A are
in a ratio of small whole numbers
carbon dioxide
12 g of Carbon &
32 g of Oxygen
O
2x
12 g of Carbon &
16 g of Oxygen
C
O
carbon monoxide
C
O
Subatomic Particles
-J.J. Thompson determined charge:mass ratio of e-, 1897
-Robert Millikan measured charge of e-, 1909
-Thompson developed “plum pudding” model of atom
-Rutherford developed “nuclear” model of atom
alpha particle
source
detector
Modern Atomic Structure
PARTICLE CHARGE * MASS (AMU)
Proton
+1
1.0073
Neutron
0
1.0087
Electron
-1
5.486 x 10-4
* unit charge = 1.602 x 10-19 C (coulomb)
 amu (u) -- atomic mass unit = 1.66054 x 10-24 g
Atomic Number

number of protons in an atom
defines an element

shown as the symbol subscript

6C
Mass Number

total number of protons plus neutrons
will vary between isotopes

shown as the symbol superscript

12C
Isotopes

elements which have the same atomic number
but different mass numbers

12C
6
13C
6
14C
6
are isotopes
Periodic Table
–Allows for organization of elements
–Allows for grouping of elements in terms of
physical and chemical characteristics
Metals, Non-metals & Metalloids
–Group 1A
Alkali Metals
–Group 2A
Alkaline Earth Metals
–Group 6A
Chalcogens
–Group 7A
Halogens
–Group 8A
Nobel Gases
–B Groups
Transition Metals
Know these !!
Molecules and Molecular Compounds
•Molecule
— the smallest particle of a compound that can be
identified as that compound
— chemical combination of two or more atoms
— a pure substance
• Chemical Formula
— a symbol representation of a molecule/compound
— shows the type and ratio of atoms in a molecule
type is given by symbol
ratio is given by a subscript to right of symbol
Examples:
Molecule
Ratio
H2O
2:1
heteroatomic
H2O2
2:2
heteroatomic
CO2
1:2
heteroatomic
CO
1:1
heteroatomic
O2
-
homoatomic
• Formulas
—Molecular Formulas
Give the type and exact number of each type of atom
—Empirical Formulas
Give only the type and simplist ratio of atoms
Molecular Formula
H2O
Empirical Formula
H2O
H2O2
HO
C6H6
CH
C2H6
CH3
— Structural Formulas
Show which atoms are attached to which atoms
C2H6O
H
H
H
C O
C H
H
H
dimethylether
H
H
H C
C
H
H
ethanol
O H
Ions & Ionic Compounds
• Some elements will either lose or gain one or
more electrons to become charged species
• Metals
– typically lose electrons, become +, cations
• Non-Metals
– typically gain electrons, become -, anions
Monatomic Ions
– made from a single element
• Na  Na+ + 1e• Cl + 1e-  Cl-
11 p+
11 e-
17 p+
17 e-
1e-
Na
Cl
+ 1e-
+
Na+
Cl-
11 p+
10 e-
17 p+
18 e-
Hints to Determine Ion Charges
• Hydrogen
+1
• Oxygen
-2
• Group IA
+1
• Group IIA
+2
• Group VIA
-2
• Group VIIA
-1
Polyatomic Ions -- “molecules”
which have a net
positive or negative charge
– CO32– NH4+
– OH-
carbonate ion
ammonium ion
hydroxide ion
Prediction of Charges -- all species tend toward the
most stable state
– Nobel gases are very stable
– Elements add or lose electrons to “mimic” nobel
gases
Ionic Compounds
• Oppositely charged ions form ionic compounds
– held together by ionic bonds due to the
electrostatic attraction between the opposite
charges
• Ionic compounds are always neutral species
• Mg2+
and
or Mg2Cl
Cl-
form MgCl2
not MgCl
Naming Inorganic Compounds
• Names of Monatomic Ions
– cations are named for the elements
Na+ is sodium ion
Fe+2 is iron(II) ion
(ferrous ion)
Cu+ is copper(I) ion
(cuprous ion)
Al+3 is aluminum ion
Fe+3 is iron(III) ion
(ferric ion)
Cu2+ is copper(II) ion
(cupric ion)
– anions are named for the root name of
the element with the ending -ide
O-2 is oxide ion
H- is hydride ion
Cl- is chloride ion
N-3 nitride ion
•Naming Polyatomic Ions
• Know the names, charges and formulas of the
important polyatomic ions
– NH4+ ammonium ion
– CO3-2 carbonate ion
– SO4-2sulfate ion
– OH- hydroxide ion
– NO3- nitrate ion
• Polyatomic ions are treated as separate entities or
units
• Naming and formula rules are the same as for
compounds with monatomic ions
Naming Binary Ionic Compounds
• Cations always named first
• Anions always named last
– NaCl sodium chloride
– BaCl2 barium chloride
• for cations which have more than one
possible charge, the charge of the ion must
be given in the name
– Fe2O3
– FeO
iron(III) oxide
iron(II) oxide
• Combinations must be neutral!
• Examples:
– 2 Na+ and
Na2CO3
1 CO3-2 is sodium carbonate
– 2 NH4+ and 1 S-2
(NH4)2S
is ammonium sulfide
– 1 Ba+2 and 2 OHBa(OH)2
is barium hydroxide
– 3 Mg+2 and 2 PO4-3 is magnesium phosphate
Mg3(PO4)2
– 1 Na+ , 1 H+ and 1 CO3-2 is sodium hydrogen
carbonate or sodium bicarbonate, NaHCO3
Acids
• A compound that produces hydrogen ions
(H+) when dissolved in water
• tastes sour
• turns litmus red
• has a pH less than 7
• typically the formula begins with one or more
H’s
– HCl(aq)
– H2SO4(aq)
– HC2H3O2(aq)
hydrochloric acid
sulfuric acid
acetic acid
Binary Acids
• Acids which contain H and another nonmetallic element
• Naming -- to the root name of the nonmetallic element:
– add the prefix hydro– add suffix -ic acid
• HF(aq) hydrofluoric acid
• HBr(aq) hydrobromic acid
• HCl(aq) hydrochloric acid
Note!
Oxyacids
• Acids which contain H and O and another
element (or H and a polyatomic anion
containing O)
• Naming -- to the polyatomic ion name
– if the suffix is -ate, change it to -ic
– if the suffix is -ite, change it to -ous
– add acid to the end of the name
• HNO3 nitric acid
HNO2 nitrous acid
• H2SO4 sufuric acid
H2SO3 sulfurous acid
• You must know polyatomic ion
Binary Molecular Compounds
• Chemical combinations of non-metals and nonmetals (no ions involved)
• The more metallic element is named first
• The second element (less metallic) is named with
the ending -ide
• Because there are no ions to use to determine
relative ratio of atoms we must indicate the number
of each atom by a prefix
– N2O3 dinitrogen trioxide
– SO3 sulfur trioxide
Name the Following:
• CaI2
calcium iodide
• Cu2O
copper(I) oxide
• CuO
copper(II) oxide
• Cl2O7
dichlorine heptaoxide
• HClO3
chloric acid
note
Write Formulas for the Following:
• calcium hypochlorite
Ca(ClO)2
• Mg+2 and ClO2-
Mg(ClO2)2
• carbon tetrachloride
CCl4
• NH4+ and SO4-2
(NH4)2SO4