Transcript isotopes - Cloudfront.net

ISOTOPES
Atom Review
All matter is made up of elements (e.g. carbon,
hydrogen, etc.).
The smallest part of an element is called an atom.
Atom of different elements contain different numbers of
protons.
The mass of an atom is almost entirely due to the
number of protons and neutrons.
The Atom
The atom consists of two parts:
1. The nucleus which contains:
protons
neutrons
2. Orbiting electrons.
Mass number = number of protons + number of neutrons
A
X
Z
Element symbol
Atomic number = number of protons
Isotopic Notation
A
X
Z
A = number of protons + number of neutrons
(mass number)
Z = number of protons (atomic number)
A – Z = number of neutrons
Number of neutrons = Mass Number – Atomic Number
ISOTOPES
 THE NUMBER OF PROTONS FOR A GIVEN
TYPE OF ATOM NEVER CHANGES.
 THE NUMBER OF NEUTRONS CAN
CHANGE.
 TWO ATOMS WITH THE SAME NUMBER OF
PROTONS BUT DIFFERENT NUMBERS OF
NEUTRONS ARE CALLED ISOTOPES.
ISOTOPES
ISOTOPES ARE
ATOMS WITH
THE SAME
NUMBER OF
PROTONS BUT
DIFFERENT
NUMBER OF
NEUTRONS.
EXAMPLES OF URANIUM ISOTOPES:
235
238
A
A
Z
Z
Number of protons
Number of protons
Number of neutrons
Number of neutrons
U
92
U
92
EXAMPLES OF URANIUM ISOTOPES:
235
238
U
92
U
92
A
235
A
238
Z
92
Z
92
Number of protons
92
Number of protons
92
Number of neutrons
143
Number of neutrons
146
Isotopes of any particular element contain the same
number of protons, but different numbers of neutrons.
So what are isotopes good for?
• Dope testing
- one of the initial tests to determine if
someone has been doping with synthetic
testosterone is a test for a high concentration of
an isotope that’s not contained within naturally
produced testosterone, but within the synthetic
testosterone derived from yams.
More tests will have to be conducted if it is revealed that the athlete is a
vegetarian with an affinity for yams.
Radiometric Dating
Making Bombs
• Uranium-235 (.72%
abundance) vs Uranium
238
– Able to go under a fission
chain reactions
– Fission = Nucleus of an
atoms can split into smaller
parts produced free
neutrons and protons.
Atomic Weight
To calculate the atomic weight
(average atomic mass) for a particular
element we must consider how much
of one isotope of an element exists
versus another isotope of the same
element. These are the "natural"
abundances (% abundance) on earth.
Rule for Calculating
Atomic Weight
To calculate the average atomic weight,
each exact atomic weight is multiplied
by its percent abundance (expressed as a
decimal). Then, add the results together
and round off to an appropriate number
of significant figures.
Example #1: Nitrogen
mass number exact weight percent abundance
14
14.003074
99.63
15
15.000108
0.37
This is the solution for nitrogen:
(14.003074) (0.9963) + (15.000108) (0.0037)
= 14.007
Practice Problem # 1
Calculate the average atomic weight for magnesium:
mass number
exact weight
percent abundance
24
23.985042
78.99
25
24.985837
10.00
26
25.982593
11.01
Answer # 1
This is the solution for magnesium:
(23.985042) (0.7899 ) + (24.985837)
(0.1000) + (25.982593) (0.1101)=
24.305