Basic Atomic
Chemistry
Early Chemistry

Early Chemists only
believed in 1 element

Later Chemists
believed in 4
elements:




Earth
Air
Fire
Water
Basic Chemistry
 Atom
= smallest unit of
matter in universe
(means “indivisible”)
 Elements are specific
kinds of an atom.
 Atoms are mostly empty
space with a nucleus at
its core and electrons at
different energy levels
around that nucleus.
Basic Chemistry

Atoms have electrons which
are very small and are
negatively charged and
have a negligible mass
(mass ≈ 0)

Electrons move in
“orbitals” around the
nucleus - at different
Energy Levels.
Basic Chemistry
 Atoms
have a Nucleus
made up of Protons &
Neutrons
 Protons are Positively
Charged and have a
mass =1 amu

Neutrons have no charge
and are therefore Neutral
& have a mass = 1 amu
+
Summary of Subatomic Particles:
Particle
Name
Location
Charge
Mass
Effect/Im
pact
Charge+
Bond
(Energy)
Mass+
Charge
Electron
Electron
Cloud
-1
≈0
Proton
Nucleus
+1
1 amu
Neutron
Nucleus
No
Charge
1 amu
Mass+Radi
oactivity
Periodic Table Notation:
 Different
elements are
represented on the Periodic
Table using this format
 The letter (symbol) is an
abbrev. of Element Name
 Atomic Number is ALWAYS
the # of protons the atom
has
Atomic Number
Determines the specific
identity of an element.
 Examples:
 Carbon = 6
 Hydrogen = 1
 Oxygen = 8
 Nitrogen = 7

Bohr Model
 Simplifies an element and its parts.
Try to make the model for Carbon,
12C
6
“Forms” of atoms
 About
100 different elements in Per. Table
… but about 2000 forms of those 100.
1. ION: same atom w/ a varying # of
electrons. Neutral atoms have EQUAL
numbers of protons (+) and electrons
(-) so overall charge = 0.
+ ions lose e’s & – ions gain e’s.
2. Isotopes:

Same atoms (the same atomic number) but
different mass numbers b/c . . .
different numbers of neutrons.
1H
1
2H
1
Isotopes of
Hydrogen
3H
1

Mass number is the total mass of
an atom in AMU = the # of protons
+ neutrons.

Remember: mass number CAN
change without changing the
identity of the element.
Average Atomic Mass
 The
atomic mass
on the Periodic
Table is not a
whole number.
 When atomic
mass is calculated
scientists use a
weighted average
Calculated by adding the
masses of each isotope ×
their relative abundances
Practice Calculation
 On
board
Ex: Hydrogen has an average atomic mass
= 1.0079. This means that most
hydrogens have an mass of 1 but a few =
2 and even fewer = 3. Thus, the average
is slightly above 1.
Q: What if hydrogen’s average atomic
mass = 1.95? What can we infer?
MARBLE LAB
Radioactive isotopes
=
unstable nucleus which decays and
gives off radiation energy.
 How
are isotopes used in biology?
1. As tracers—organisms use
elements regardless of it isotopic form, so
scientists can label and follow a
chemical’s path.
Suppose a runner has severe pain
in his shin. The Dr. decides to
check to see if the tibia has a
stress fracture. The runner is given
an injection w/ Technetium—99m.
This radioisotope is a gamma ray
producer with a half-life of 6 hours.
After a several hour wait, the
patient undergoes bone imaging.
Any area of the body that is
undergoing unusually high bone
growth will show up as a stronger
image on the screen. If the runner
has a stress fracture, it will show up
on the bone imaging scan.
2. Verifying Climate Change is
in part human caused.
#1 In the last 150 years we have increased
the production of CO2 via industrial waste
and by deforestation (we can measure
how much).
Relationship between global temperatures
and CO2 levels
How do we know it is from fossil fuels and
not from the earth itself?
 Industrial
Revolution and beginning of CO2
increase coincide
 Carbon dating implicates humans
 CO2
from burning fossil fuels or
forests has quite a different isotopic
composition from CO2 already in the
atmosphere--because plants have a
preference for the lighter (faster
moving) isotopes (12C vs. 13C). Thus
they have lower 13C/12C ratios than
that of the atmosphere.
 Since
fossil fuels are derived from
ancient plants, plants and fossil fuels
all have roughly the same 13C/12C ratio
– about 2% lower than that of the
atmosphere. As CO2 from these
materials is released and mixes with
the atmosphere, the average 13C/12C
ratio of the atmosphere has decreased
(Real Climate: Climate Science from Climate
Scientists)
3. Radiometric dating (p. 540-1)
Every unstable isotope decays at a
constant rate called half-life = the time it
takes a given amount of an isotope to
decay to half of its original amount.
Example
 Carbon
dating. C-14 and C-12 are two
different isotopes of carbon. The ratio of
C-12 to C-14 in living tissue is relatively
constant from one organism to the next.
But what happens after the organism
dies?
 The
amount of C-14 will go down
compared to the amount of C-12. Why?
Practice Problems (in notes ok)
½ life of Carbon-14 ≈ 5730 years.
How old would a fossil be if it contains 1g
of C-14 compared to a living sample of
equal mass that has 8 g of C-14?
 The
 What
amount (% or fraction) of C-14
would you be left after 4 half-lives?
 HW:
p. 569 #6,7
Honors
 Go
to this web site:
http://www.physlink.com/Education/askExperts/ae
403.cfm <or use the internet to research>
Answer these questions.
1. What does C-14 decay into?
2. If C-14 is decaying, why hasn’t it just all
disappeared over time?
3. Why is C-14 not good to use when dating things
less than a 10 years or more than 1 million
years old?