MODELS OF THE ATOM
CHM 130
GCC
Review - Rounding
• Round 399
Hopefully you said 400 not 4. What is
wrong with 4???
The zeroes ARE important, they are place
holders. 400 and 4 are NOT the same! If you
had $400 in the bank but they said you had only
$4 you’d be pissed off!
Round 2389 to 2 sig fig, now round to 1 sig fig
Answer: 2400 NOT 24
2000 NOT 2
5.1 DALTON’S ATOMIC THEORY
1. An element is made of tiny,
indestructible particles called
atoms. (Not quite true – why?)
2. All atoms of an element
are identical and have the
same properties.
(Not quite true – why?)
3. Atoms of different
elements combine to form
compounds.
+
4. Compounds contain atoms in
small whole number ratios.
e.g. Each H2O molecule consists
of one O and two H atoms, not
½ atoms or ¾ atoms.
5. Atoms of 2 or more
elements can combine to form
different compounds.
E.g. C and O may form CO or CO2
5.2 Thomson cathode ray experiment
Thompson “Plum Pudding Model”
http://highered.mcgrawhill.com/sites/0072512644/student_view0/
chapter2/animations_center.html#
•Atom is + charged
-
-
-
+
•e-’s are distributed
throughout atoms
like raisins in plum
pudding
-
-
5.3 Rutherford’s Scattering Experiment
http://www.mhhe.com/physsci/chemistry/animati
ons/chang_2e/rutherfords_experiment.swf
Explanation of Scattering
Nuclear Model
1) The atom is mostly empty space with
electrons moving around.
2) Each atom has a small, dense
nucleus with the Protons & Neutrons.
Rutherford’s model
atom (~10-8 cm diameter)
-
+
nucleus
(~10-13 cm diameter)
-
-
If nucleus = size of a small marble, then atom
is the size of Cardinal’s stadium!
Subatomic Particles
Particles
Electrons
Symbol Charge
Relative Mass (amu)
-
-1
1/1836
+
+1
1
0
1
e
Protons
p
Neutrons
n
5.4 Atomic Notation
ATOMIC NUMBER
Every atom of an element has the same
# of protons
The # of protons defines an element
Carbon atoms ALWAYS have 6 protons
Mass number
Mass number = # protons + neutrons
So how calculate # neutrons?
# neutrons = mass - # protons
Isotopes
Isotopes of an element have the same
atomic number (# pro), but a different
mass number (# neu).
Ex: carbon-12, carbon-13 and carbon-14
How many protons do the above have?
Neutrons? 6, 7, 8
6
Ex. 1: Write the atomic notation for
potassium-40.
40
19
K
How many neutrons are there?
40 – 19 = 21
______________
Ex. 2: a. Write the atomic notation
for bromine-81.
81
35
Br
b. How many neutrons are there?
_________________
81 - 35 = 46
Isotope
oxygen-16
oxygen-17
oxygen-18
mass #
16
17
18
# protons # neutrons # electrons
8
8
8
8
9
10
8
8
8
5.5 Atomic Mass
Masses of atoms are so small that we
define the atomic mass unit (amu)
•Mass of proton & neutron  1 amu.
•Mass of electron is basically zero amu
Atomic mass
Atomic Mass in the P. Table
is the weighted average of
all atoms for that element
in the world, so that is why
it is NOT a whole number.
Natural isotopes of carbon:
carbon-12 (98.89%)
carbon-13 (1.11%)
The atomic mass reported for carbon
(12.01 amu) is closer to carbon-12
since it is most abundant isotope for
C. (There is a ton more C-12 than C13.)
Example: Use the Periodic Table to
determine the most abundant
isotope:
a.
lithium-6 or lithium-7
b. chlorine-35 or chlorine-37
5.6 Light has two components:
Wavelength () is the distance
between peaks
Frequency () is the number of wave
cycles per second. (like a beat)
• As wavelength , the frequency ,
and the energy 
Which wave has higher
energy? Lower frequency?
Radiant Spectrum:
5.7 In 1900, Max Planck
proposed the controversial idea
that energy was emitted in
small bundles called quanta.
• a particle of light energy is
called a photon
Ball loses potential
energy continuously
as it rolls down a
ramp.
Ball loses potential
energy in quantized
amounts as it bounces
down a stairway.
5.8 Bohr Model
~1913
Neils Bohr proposed that electrons
orbit around the nucleus, occupying
orbits with distinct energy levels.
Electrons are quantized!
Bohr model of the atom
• The electrons orbit around the nucleus
kinda like planets orbit around the sun
but in 3D.
• These orbits are called energy levels or
shells.
• Each orbit has a specific radius and
energy, so a certain distance from the
nucleus.
Bohr Model
The orbit closest to
the nucleus is lowest
in energy; the energy
increases with
distance from the
nucleus. Proven by
line spectra.
When the light from a heated element passes
through a prism, a series of narrow lines is
seen.
These lines are the emission line spectrum.
Atomic Fingerprints
Each element produces a different
emission line spectrum, so its own
unique color.
Each element has it’s own
energy levels that are unique.
Bohr theory explains 3 lines in H2 spectra.
• Electrons gain energy from heat or electricity and
jump to a higher energy level. These “excited”
electrons ultimately lose energy and drop to lower
energy levels, which causes light to be emitted.
5.9 Each Energy Level Can
Be Subdivided Into
Sublevels.
Levels:
sublevels:
1-7
s, p, d, and f.
Each Level Has n Sublevels:
1st level has One Sublevel 1s
2nd level has Two Sublevels 2s 2p
3rd level - Three Sublevels 3s 3p 3d
4th level - Four Sublevels 4s 4p 4d 4f
This is depicted on next slide.
Orbitals are regions in space where
there is a high probability of finding
an electron.
– One orbital can hold a maximum of 2
electrons.
Each sublevel contains a specific
number of orbitals.
s has 1 orbital
p has 3
d has 5
f has 7
Orbitals are boxes on next slide
5.10 Electron Configuration:
Shorthand description of electrons
by sublevel.
• Sublevels are filled in order of increasing
energy.
1s < 2s < 2p < 3s < 3p < 4s
– You will do configurations for the 1st 20
elements.
– Note the 3d sublevel is higher in energy
than the 4s which is why we fill 4s first
Writing electron configurations
1. # of electrons?
2. Fill in sublevels to reach that #
3. Use superscript numbers to indicate
number of e-'s in each sublevel.
Ex: C is 1s22s22p2
(cause 6 electrons)
Practice writing econfigurations
2
2
6
1
• 1s 2s 2p 3s
• Na
2
2
4
• O • 1s 2s 2p
2
2
6
2
6
2
• Ca • 1s 2s 2p 3s 3p 4s
2
2
2
• C • 1s 2s 2p
The Periodic Table
actually is arranged by
s, p, d, and f sublevels.
5.11 S Orbitals
1s
2s
3s
P Orbitals
Cool orbital pictures
http://winter.group.shef.ac.uk/orbitron/
Ch. 5 Self Test p. 140
• Try # 1-4, 6-7, 9, 12, 14-15, 17-18
• Answers in Appendix J
• Try to answer first, then check your
answer!
• Also work the problems in the online
NOTES and worksheets.