Unit 3
Atomic Theory
Atom
Smallest particle possessing the
properties of an element.
Nucleus
Dense, positively charged central
region that contains protons and
neutrons.
Protons
Positively charged subatomic
particles that are found in the
nucleus
Neutrons
Neutral subatomic particles (have
no electrical charge) that are
found in the nucleus.
Electron Cloud
Different energy levels
surrounding the atom’s nucleus
where electrons can be found.
Electrons
Negatively charged subatomic
particles that surround the
nucleus.
Atomic Number
The number of protons in an
atom.
Atomic Mass
The relative average mass of an
atom of an element as found in
nature.
Atomic mass = # of protons + # of
neutrons.
II: Atomic Particles
Particle
Proton
Mass
Location
Charge
1 AMU Nucleus
Positive
Neutron 1 AMU Nucleus
Neutral
Electron 0 AMU Electron
cloud
Negative
Isotopes
Atoms of the same element that
have a different number of
neutrons.
Isotopes


Two (2) or more atoms of the same element with
a different mass.
Percent (%) abundance:
Protium, Deuterium, Tritium
99.985%, 0.015%,
0%
Self Check
1. What two subatomic particle are
found in the nucleus?
A. Neutrons and Electrons
B. Protons and Electrons
C. Neutrons and Protons
D. Neutrons only
Self Check
2. The atomic number is equal to the
_______.
A. Number of neutrons in an atom.
B. Number of electrons in an atom.
C. Number of neutrons plus the
number of protons in an atom.
D. Number of protons in an atom.
Self Check
3. Isotopes are atoms of the same
element that have a different
number of ______.
A. Neutrons
B. Protons
C. Electrons
D. All of the above
Self Check
4. The element with an atomic number
of 14 is?
A. Nitrogen
B. Silicon
C. Aluminum
D. Sulfur
Important Number Stuff


Atomic number is
equal to the
number of protons
(and electrons in a
neutral atom)
Atomic Mass is the
sum of protons and
neutrons
Examples…
Element
#
protons
#
neutrons
#
electrons
5
6
5
10.811
Sulfur 16
16
16
32.006
Gold
118
79
196.96
Boron
79
Ave.
Atomic
mass
Sample—look at “2_weighted ave.”
 Of
100 marbles:
– 25 have a mass of 2.00g
– 75 have a mass of 3.00g
– What is the average mass?
 25%

= 0.25
75% = 0.75
(0.25 x 2.00) + (3.00 x 0.75) = Ave Mass
 0.5
+
2.25 = 2.75
Sample with Atoms
Copper 63 amu = 69.17%
 Copper 65 amu = 30.83%
 Calculate the Average
atomic mass

Continued…
Copper 63 amu = 69.17
 Copper 65 amu = 30.83
 Calculate the Average atomic mass

(63 x 0.6917) + (65 x 0.3083)
 63.617 AMU

– Check on periodic table
Ions
Electrically charged atoms or
groups of atoms.
Cations = positively charged
Anions = negatively charged
I: Models of the atom over time
 Democritus:
fifth century BC Philosopher
– First to describe matter as made of tiny
particles
 John
Dalton: “Billiard ball” theory 1803
– Atom = small solid sphere
 In
an element = all the same “sphere”
 Different elements = different “sphere”
 Compounds = different spheres combined in
different ratios
Continued…

JJ Thompson: 1897
“Plum Pudding”
model
– Atom = sphere of +
and – particles
– Discovered the
electron = Nobel
prize
Continued

Ernest Rutherford:
1908
– Atom = mostly
empty space
+
nucleus
 - electrons outside

Niels Bohr: 1913
– Electrons traveled
in circular orbits
Continued…

Electron Cloud
Model: 1920’s
– Atom = Dense
nucleus of + protons
and neutral
neutrons.
– Electrons surround
nucleus in “clouds”
of different NRG
levels.
(NRG =Numerical
Renormalization
Group)
Elements on the Periodic Table
1
Hydrogen
H
1.008
Self Check
5. Draw a picture of what Iron in its
neutral state would look like on the
periodic table.
Hint:
Self Check Answers
1.
2.
3.
4.
5.
C
D
A
B
26
Iron
Fe
55.85
III. Molar
Conversions
A. What is the Mole?
A
counting number (like a dozen)
 Avogadro’s
1
number (NA)
mol = 6  1023 items
A
large
amount!!!!
1
A. What is the Mole?
mole of hockey pucks would
equal the mass of the moon!
1
mole of basketballs would fill
a bag the size of the earth!
1
mole of pennies would cover
the Earth 1/4 mile deep!
 The
B. Molar Mass
mass of 1 mole of an element
or compound. Round to nearest
whole number (except chlorine)
 Atomic
weight label:
– amu/atom or g/mol
 Molecular
weight label:
– amu/molecule or g/mol
B. Molar Mass Examples
 carbon
12 g/mol
 aluminum
27 g/mol
 zinc
65 g/mol
B. Molar Mass Examples
 water
– H2O
– 2(1) + 16 = 18 g/mol
 sodium
chloride
– NaCl
– 23 + 35.5 = 58.5 g/mol
B. Molar Mass Examples
 sodium
bicarbonate
– NaHCO3
– 23 + 1 + 12 + 3(16)
= 84 g/mol
 sucrose
– C12H22O11
– 12(12) + 22(1) + 11(16)
= 342 g/mol
C. Molar Conversions
molar
mass
6  1023
MASS
NUMBER
MOLES
IN
GRAMS
OF
PARTICLES
(g)
(atoms/molecules)
C. Molar Conversion Examples
 How
many moles of carbon
are in 26 g of carbon?
26 g C 1 mol C
12 g C
= 2.17 mol C
C. Molar Conversion Examples
 How
many molecules are in
2.50 moles of C12H22O11?
2.50 mol 6  1023
C12H22O11 molecules
1 mol
= 1.5  1024
molecules
C12H22O11
C. Molar Conversion Examples
 Find
the mass of 2.5 moles of
NaHCO3.
2.5 mol
NaHCO3
84 g
1 mol
= 210 g NaHCO3
Patterns on the Periodic Table