atoms & isotopes mrs. page chemistry10 parts of presentation modified from a powerpoint...
TRANSCRIPT
ATOMS & ISOTOPESMrs. 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 Observed by E. Goldstein in 1896
Rutherford is given credit for showing Rutherford is given credit for showing
that atoms contain both negatively and that atoms contain both negatively and
positively charged particles (gold foil positively charged particles (gold foil
experiment)experiment)
Has a charge of +1 Has a charge of +1
Relative Mass of 1 AMU (1.673 x 10Relative Mass of 1 AMU (1.673 x 10-24-24 g) g)
NEUTRON
Third major subatomic Third major subatomic particle discovered (1932 particle discovered (1932 James Chadwick)James Chadwick)
No charge (neutral)No charge (neutral) Relative Mass of 1 AMU Relative Mass of 1 AMU
(1.675 x 10(1.675 x 10-24-24 g) g)
ISOTOPES
Atoms of the same element Atoms of the same element have the same atomic number have the same atomic number (# of protons) and the same (# of protons) and the same chemical properties.chemical properties.
However, atoms of the same However, atoms of the same element may have different element may have different numbers of neutrons (and numbers of neutrons (and therefore different atomic therefore different atomic mass)mass)
IsotopesIsotopes are atoms of the same are atoms of the same element having different element having different number of neutronsnumber of neutrons
NATURALLY OCCURRING ISOTOPES
Every element has naturally occurring Every element has naturally occurring isotopesisotopes
Hydrogen has 3 naturally occurring Hydrogen has 3 naturally occurring isotopesisotopes Protium is the most abundant isotope of Protium is the most abundant isotope of
hydrogen (99.985%) has 1 proton, 0 hydrogen (99.985%) has 1 proton, 0 neutrons, and 1 electronneutrons, and 1 electron
Deuterium (0.015%) has 1 proton, 1 Deuterium (0.015%) has 1 proton, 1 neutron, and 1 electronneutron, and 1 electron
Tritium (0.0001% ?) has 1 proton, 2 Tritium (0.0001% ?) has 1 proton, 2 neutrons, and 1 electronneutrons, and 1 electron
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 13C 14C 6 6 6
#P _______ _______ _______
#N _______ _______ _______
#E _______ _______ _______
SOLUTION
12C 13C 14C 6 6 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
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
Na22.99
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 Abundance
24Mg = 24.0 amu 78.70%
25Mg = 25.0 amu 10.13%
26Mg = 26.0 amu 11.17%(24)(.787) + (25)(.1013) + 26(.1117) =
18.888 + 2.5325 + 2.9042 = 24.3 amu
ISOTOPES
Two CategoriesTwo Categories Unstable – isotopes that Unstable – isotopes that
continuously and continuously and spontaneously break spontaneously break down/decay in other lower down/decay in other lower atomic weight isotopesatomic weight isotopes
Stable – isotopes that do not Stable – isotopes that do not naturally decay but can exist naturally decay but can exist in natural materials in in natural materials in differing proportionsdiffering proportions
USES OF RADIOISOTOPES Carbon 14 Dating (Geologic Time)Carbon 14 Dating (Geologic Time)
When the organism dies it stops taking in When the organism dies it stops taking in 1414C which C which disappears as it decays to disappears as it decays to 1414NN
Americum-241Americum-241 Used in smoke detectors Used in smoke detectors
Cesuim-137 Cesuim-137 Used to treat cancerous tumorsUsed to treat cancerous tumors
Californium-252Californium-252 Used to inspect luggage for Used to inspect luggage for explosivesexplosives
Cobalt-60 Cobalt-60 Used to sterilize surgical equipmentUsed to sterilize surgical equipment
Iodine-123Iodine-123 Used to treat thyroid disorders Used to treat thyroid disorders
Plutonium-238Plutonium-238 Used to power NASA Used to power NASA spaceshipsspaceships