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Isotopes
1. THE NATURE OF MATTER
Chapter # 02
Topic :ISOTOPES
Objective
Define nucleon number
Define and state isotope of same atoms with
different nucleon number
3. ATOMIC STRUCTUREATOMIC STRUCTURE
the number of protons in an atom
the number of protons and
neutrons in an atom
HeHe
22
44Atomic mass
Atomic number
number of electrons = number of protons
4. 4
O
16
8
chemical symbol
mass number
(nucleon number)
proton number
(atomic number)
P=E
No. of
protons= no.
of electrons
atomic number (proton number) is the number of
protons in an atom.
Each oxygen atom has 8 protons.
As the number of electrons is equal to the number of
protons in an atom, each oxygen atom contains 8
electrons.
Mass=P+N
mass number is the total number
of protons and neutrons in an
atom.
Number of neutrons in the
oxygen atom is: 16 – 8 = 8.
Interpreting Chemical Symbol
5. Definition of Isotopes
Isotopes are atoms of the same
element which contains the same
number of protons but different
number of neutrons.
10. 10
The atomic mass of an element
• is listed below the symbol of each element on
the periodic table.
• Gives the mass of an “average” atom of each
element compared to 12C.
11. 11
The calculation for atomic mass requires the
• percent(%) abundance of each isotope.
• atomic mass of each isotope of that element.
• sum of the weighted averages.
mass of isotope(1)x (%) + mass of isotope(2) x (%) =Ar
100 100
Ar=(Average atomic mass)
12. 12
24Mg = 23.99 amu x 78.70/100 = 18.88 amu
25Mg = 24.99 amu x 10.13/100 = 2.531 amu
26Mg = 25.98 amu x 11.17/100 = 2.902 amu
Atomic mass (average mass) Mg = 24.31 amu
16. Stable vs. Unstable
• A stable isotope does NOT
undergo radioactive (or nuclear)
decay.
• An unstable isotope undergoes
radioactive (or nuclear) decay.
Unstable isotopes are also known
as radioisotopes or radionucleides
17. Uses of Radioactive Isotopes
• Food irradiation
• Archaeological dating (carbon-dating)
• Smoke detectors
• Radioactive tracers
22. • Stable isotopes:
• They do not naturally decay but exist in
natural materials in differing proportions
• Unstable iso tope
• Isotopes that continously break down into
lower atomic weight isotopes