Atoms, Molecules, and
Ions
Chapter 2
Democritus
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460 BC
First to propose
atomic nature of
matter
“atomos” indivisible
Dalton
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Studied
experiments from
other scientists
Law of multiple
proportions
First Modern Atomic
Theory
Dalton’s Postulates
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Each element is composed of tiny
particles
All atoms of an element are identical
Atoms of an element are not changed
into different types of atoms in a chem
rxn
Compounds form when 2 or more
atoms combine
J.J. Thomson
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Cathode ray
experiments
Discovered
electrons and their
charge-to-mass
ratio
Plum Pudding
Model of Atom
Plum Pudding Model
electrons
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JJ Thomson
1897
Electrons float in a
positively charged
ooze.
No nucleus
Positively charged ooze
Millikan
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Oil drop experiment
Determined the
charge of the
electron as
-1
Rutherford
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1911 - Gold foil
experiment
Discovered that the
atom was mostly
empty space with a
small dense positively
charged core he called
the nucleus
Also discovered
protons in 1919
The Nuclear Model
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1911
Rutherford
*Nucleus: positively
charged center
Electrons orbit the
nucleus
*Atom is mostly
empty space.
Chadwick
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Discovered neutron
in 1932
Neutrons are about
the same size as a
proton, but have no
charge.
Found in nucleus
Bohr
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Planetary model of
atom in 1913
Wavelengths of
emissions of
hydrogen spectrum
Bohr’s Model
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1913
Electrons orbit the
nucleus in specific
energy levels
Electrons can jump
between energy levels
Each energy level
holds a specific
number of electrons
nucleus
n=1
n=2
Energy levels
Electron cloud model
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Schrodinger
1926
We now know that
electrons move very
fast around the
nucleus.
This fast movement
causes the electrons
to form a “cloud”
around the nucleus.
The cloud is a
mathematical
probability of where
the electrons are in
orbit.
Marie Curie
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Radiation
Discovered radium
and polonium
Used X-ray
machines in WWI
Becquerel
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Discovered
radiation
Worked with Curies
Discovery of Atomic Structure
What is it?
characteristics
Alpha
particles
(α)
Beta
particles
(β)
Helium nucleus
(4He)
2 protons, 2 neutrons,
positive charge
Weakest
High speed eemitted from
nucleus at time of
creation
-1 charge
Weak
Gamma
particles
(γ)
High energy X-ray
Strongest
Cause and cure
cancer
Modern View of Atomic
Structure
Protons Neutrons Electrons
Location Nucleus Nucleus
Moving very fast in energy
levels around nucleus
Relative
size
Charge
Large
Large
Extremely tiny
+1
0
-1
Symbol
p+
n0
e-
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Atomic Mass - based on #s of protons,
neutrons, and electrons in the atom
protons and neutrons have about the
same mass and size; found in the
nucleus; make up almost ALL of the
mass of the atom
electrons are extremely tiny, have
almost NO mass
on periodic table, atomic mass is
AVERAGE atomic mass
Isotopes
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isotopes - atoms of an element
that have different masses
same # of p+, different
# of n
Some symbols, formulas,
and terms
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A = mass number = protons +
neutrons
Z = atomic number = protons =
electron (neutral atom)
number of neutrons = mass # protons = A-Z
Isotopic notation
Element-A
AX
X-A
Neon - 20
20Ne
Ne-20
Cobalt - 60
60Co
Co-60
Average Atomic Mass
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Average of all the isotopes found in
nature
Naturally occurring chlorine is 75.78%
35Cl, which has an atomic mass of
34.969amu and 24.22% 37Cl, which
has a mass of 36.966 amu. Calculate
the average atomic mass.
Practice problem on page 46.
Development
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Dobereiner
– Triads – groups of 3 based on similar
properties
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Newlands
– Law of octaves – same properties repeat
every 8th element
– 7 rows of 7 elements each
Mendeleev
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Father of the Periodic Table
Elements were put into columns
according to properties and increasing
atomic mass.
Rows varied in length.
LEFT BLANK SPOTS FOR
UNDISCOVERED ELEMENTS.
Properties of the elements depends on
atomic mass.
Moseley
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Used X-rays to study protons in the
atoms
He noticed that atomic number
increased according to Mendeleev’s
chart.
Led to modern periodic law
Periodic Law, based on
Moseley’s Work
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The properties of the elements are a
periodic function of their atomic
number.
That is, the properties of the elements
depends on the atomic #.
Organization
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Mendeleev
Elements are arranged according to their
properties.
Each group or family (vertical columns)
have similar properties.
Each horizontal row is called a period.
The A groups (columns 1,2,13-18) are
representative elements.
The B groups (columns 3-12) are transition
elements.
Family Names
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Group IA (1) – Alkali Metals
Group IIA (2) – Alkaline Earth Metals
Group VIA (16) – Chalcogens
Group VIIA (17) – Halogens
Group VIIIA (18) – Noble Gases
Groups 3-12 – Transition Metals
Top Row – Lanthanides
Bottom Row - Actinides
Valence Electrons
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Electrons in the outermost energy
level of the atom.
Electrons most responsible for atom
behavior.
Valence Electrons
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Alkali Metals – 1
Alkaline Earth Metals – 2
Boron Group (13) – 3
Carbon Group (14) – 4
Nitrogen Group (15) – 5
Chalcogens – 6
Halogens – 7
Noble Gases - 8
Stability
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Ultimate goal: to become stable
Octet rule: 8 valence electrons make an atom
stable because that completes the outer
energy level; full = stable
Atoms want to achieve a noble gas electron
configuration – isoelectronic.
Some exceptions: a full or half-full sublevel
will also make an atom relatively stable
Properties of Metals
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Good conductors of heat & electricity
Malleable (pounded into sheets)
Ductile (stretched into wires)
Hard, shiny appearance
3 or less valence electrons
Lose electrons to form compounds
Left side of PT
Properties of Nonmetals
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Poor conductors of heat & electricity
Good insulators
Solids are dull and brittle.
Most are gases at room temperature.
5 or more valence electrons
Gain electrons to form compounds
Right side of PT
Properties of Metalloids
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Semiconductors
Share electrons to form compounds
Both metallic and nonmetallic
properties
Follow stair-step line
Molecules - Two or more
atoms tightly bound together
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Chemical formulas
– H2O
– Ca3(PO4)2
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Diatomic molecules
– Br2I2N2Cl2H2O2F2
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Molecular compounds
– Composed of molecules and contain more
than one type of atom
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Most contain only nonmetals
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Molecular formula
– Actual numbers and types of atoms
– H2O; C6H6
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Empirical formula
– Only gives the ratio of atoms
– H2O; CH
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Structural formula
– Shows how atoms are bonded
Ions and Ionic
Compounds
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Ion – charged particle
Cation – positive ion
Anion – negative ion
Polyatomic ions – atoms joined in a
molecule, but with an overall charge
Charges (Oxidation
numbers)
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Pattern on PT
Transition metals vary
– Can be determined from formula
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CuCl2
– Are denoted with roman numerals
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Iron (III) nitrate
Writing Formulas
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MUST HAVE CHARGES TO WRITE
FORMULAS!!!
Sodium chloride
Barium bromide
Copper (II) sulfate
Iron (III) nitrate
Magnesium phosphate
Binary Compounds
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Metal-nonmetal compound consisting
of 2 elements
– Name the cation.
– Name the anion by changing the ending
to –ide.
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Example: NaCl – sodium chloride
Example: Li2S – lithium sulfide
Naming Compounds
Containing Polyatomic Ions
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1. Name the cation.
2. Name the anion. Do NOT change
the ending of a polyatomic ion.
Example: NaSCN – sodium
thiocyanate
Example: CaCO3 – calcium carbonate
Example: NH4Cl – ammonium chloride
Transition Metals (except
Ag+, Zn+2, Cd+2)
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Determine charge of cation by looking
at the formula and the anion.
Name the cation, indicating charge
using Roman numerals in parentheses.
Name the anion.
Example: FeCl3 – iron (III) chloride
Example: PbSO4 – lead (II) sulfate
Acids
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If the compound has an H as a cation,
it is usually an acid.
HCl, HBr, HI, HNO3, HClO4, H2SO4
– Know these 6 strong acids
Naming acids containing
H and a nonmetal
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1. Determine the root of the nonmetal.
2. Place the prefix “hydro” in front of
the base.
3. Change the ending to –ic and add
the word “acid”
Example: HCl: hydrochloric acid
Example: HBr: hydrobromic acid
Example: HI: hydroiodic acid
Naming Acids containing
polyatomic ions
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Name the polyatomic ion, changing
the ending as follows:
– -ate  -ic acid
– -ite  -ous acid
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Example: HNO3: nitric acid
Example: HNO2: nitrous acid
Naming compounds
containing 2 nonmetals
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Name the compound following the rules for
binary compounds and add prefixes to
indicate the number of each atom in the
compound.
Prefixes:
–
–
–
–
–
Mono – 1
Di- 2
Tri – 3
Tetra – 4
Penta – 5
hexa - 6
hepta - 7
octa - 8
nona - 9
deca - 10
Naming compounds
containing 2 nonmetals
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Example: S2O8 : disulfur octoxide
Example: P3N5 : triphosphorous
pentanitride
Example: CO: carbon monoxide
Example: CO2: carbon dioxide
Polyatomic Ions
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Ions that consist of more than one atom
Know the ones for the quiz; list for others
Naming of Pis with O
– Most common form –ate; ClO3- chlorate
– One less O: -ite; ClO2- chlorite
– Two less O: hypo<root>ite; ClO- hypochlorite
– One more O: per<root>ate; ClO4- perchlorate