Isotope PPT - MrsPage.com
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ATOMS & ISOTOPES
Mrs. Page
Chemistry10
Parts of presentation modified from a PowerPoint presentation prepared by
J. Crelling, Southern Illinois University
LEARNING OBJECTIVES
• You will be able to define what an isotope is.
• You will be able to determine the number of protons,
neutrons, and electrons in different isotopes of the
same element.
• You will understand that atomic mass
• You will understand what radioactivity is the average of
the naturally occurring isotopes of an element.
• You will be able to give examples of how radioisotopes
are used in industry and medicine.
ATOMS
Contain protons, neutrons, and electrons
Protons & neutrons are found in the
nucleus
The nucleus contains most of the mass of
an atom
Electrons are distributed around the
nucleus in energy levels/shells/orbitals
(which make up the electron cloud)
The outermost electrons in the shell
farthest from the nucleus are called
valence electrons
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ELECTRONS
First
subatomic particle discovered
1897 J.J. Thomson used the cathode ray
tube to discover the electron
Has a negative charge (-1)
Mass = 9.110 x 10-28 g (0.0005 amu)
Electrons are located in energy levels
which make up the electron cloud
Electrons in the outermost energy level
are called valence electrons
Valence electrons are responsible the for
the reactivity of an atom.
PROTON
Observed by E. Goldstein in 1896
Rutherford is given credit for showing that atoms
contain both negatively and positively charged
particles (gold foil experiment)
Has a charge of +1
Relative Mass of 1 AMU (1.673 x 10-24 g)
NEUTRON
Third
major subatomic particle
discovered (1932 James
Chadwick)
No
charge (neutral)
Relative
Mass of 1 AMU (1.675
x 10-24 g)
ISOTOPES
Atoms
of the same element have
the same atomic number (# of
protons) and the same chemical
properties.
However,
atoms of the same
element may have different
numbers of neutrons (and therefore
different atomic mass)
Isotopes
are atoms of the same
element having different number of
neutrons
NATURALLY OCCURRING ISOTOPES
Every
element has naturally occurring isotopes
Hydrogen
Protium
has 3 naturally occurring isotopes
is the most abundant isotope of
hydrogen (99.985%) has 1 proton, 0 neutrons,
and 1 electron
Deuterium (0.015%) has 1 proton, 1 neutron,
and 1 electron
Tritium (0.0001% ?) has 1 proton, 2 neutrons, and
1 electron
ISOTOPE EXAMPLE
35Cl
37Cl
17
17
chlorine - 35
chlorine - 37
ISOTOPES OF CARBON
Naturally occurring carbon consists of three isotopes, 12C, 13C, and
14C. State the number of protons, neutrons, and electrons in each of
these carbon atoms.
12C
6
13C
6
14C
6
#P _______
_______
_______
#N _______
_______
_______
#E _______
_______
_______
SOLUTION
12C
6
13C
6
14C
6
#P __6___
_ 6___
___6___
#N __6___
_ _7___
___8___
#E __6___
_ 6___
___6___
ZINC PROBLEM
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
B.
Number of neutrons in the zinc atom
C. What is the mass number of a zinc isotope
with 37 neutrons?
ATOMIC MASS
Na
22.99
Listed on the periodic table
Gives the mass of “average” atom of each element
compared to 12C
Average atom based on all the isotopes and their
abundance %
Atomic mass is not a whole number … mass number is a
whole number
CALCULATING ATOMIC MASS
Percent(%) abundance of isotopes
Mass of each isotope of that element
Weighted average =
mass isotope1(%) + mass isotope2(%) + …
100
100
ATOMIC MASS OF MAGNESIUM
Isotopes
Mass of Isotope
24Mg
= 24.0 amu
25Mg
=
25.0 amu
26Mg
=
26.0 amu
Abundance
78.70%
10.13%
11.17%
(24)(.787) + (25)(.1013) + 26(.1117) =
18.888 + 2.5325 + 2.9042 = 24.3 amu
ISOTOPES
Two Categories
Unstable
– isotopes that
continuously and spontaneously
break down/decay in other lower
atomic weight isotopes
Stable – isotopes that do not
naturally decay but can exist in
natural materials in differing
proportions
USES OF RADIOISOTOPES
Carbon
14 Dating (Geologic Time)
When the organism dies it stops taking in 14C which
disappears as it decays to 14N
Americum-241 Used in smoke detectors
Cesuim-137 Used to treat cancerous tumors
Californium-252 Used to inspect luggage for
explosives
Cobalt-60 Used to sterilize surgical equipment
Iodine-123 Used to treat thyroid disorders
Plutonium-238 Used to power NASA spaceships