Lecture1'4: Isotopes and the Atomic Mass Unit

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Lecture-1.4 Isotopes and the Atomic Mass Unit
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Isotopes and the Atomic Mass Unit

• Recall...
• A Nuclide is an atom in which the number of
  protons and neutrons are specified.
• OR
• A Nuclide is an atom whose atomic number and
  mass number are specified.

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Isotopes and the Atomic Mass Unit

• Recall...
• The atoms of each element has its own unique
  number of protons called the atomic number.
• Recall...
• The number of electrons in an atom is equal to
  the number of protons.

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Isotopes and the Atomic Mass Unit

• The number of neutrons in atoms of the same
• element can vary.
• Hydrogen atoms always have one proton and
• one electron but...
• Hydrogen-1 atoms have zero neutrons.
• Hydrogen-2 atoms have one neutron.
• Hydrogen-3 atoms have two neutrons.

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Isotopes and the Atomic Mass Unit

• isotopes are atoms with the same number of
• protons but a different number of neutrons.
• Recall...
• The total number of protons in an atom is
• called the atomic number.
• Recall...
• The total number of protons and neutrons in
• an atom is called the mass number.
• isotopes are atoms with the same atomic
• number but a different mass number.

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Isotopes and the Atomic Mass Unit

• Consider the following isotopes of carbon.
• C-12 has ___ protons and ___ neutrons.
• C-14 has ___ protons and ___ neutrons.
• C-14 has ___ protons and ___ neutrons.

6
6
6
7
6
8
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Isotopes and the Atomic Mass Unit

• Consider the following isotopes of chlorine.
• Cl-35 has ___ protons and ___ neutrons.
• Cl-37 has ___ protons and ___ neutrons.

17
18
17
20
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Isotopes

• Consider the following isotopes of magnesium.
• Mg-24 has ___ protons and ___ neutrons.
• Mg-25 has ___ protons and ___ neutrons.
• Mg-26 has ___ protons and ___ neutrons.

12
12
12
13
12
14
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Isotopes and the Atomic Mass Unit

• Write the nuclide symbol for the isotope that has
  28 protons and 30 neutrons.
• Write the nuclide symbol for the isotope that has
  8 protons and 10 neutrons.

Ni
58
28
O
18
8
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Isotopes and the Atomic Mass Unit

• Write the nuclide symbol for the isotope that has
  13 protons and 14 neutrons.
• Write the nuclide symbol for the isotope that has
  92 protons and 146 neutrons.

Al
27
13
U
238
92
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Isotopes and the Atomic Mass Unit

• Recall...
• The masses of the proton, neutron, electron
• are all rounded to the nearest whole number.

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Isotopes and the Atomic Mass Unit

• In fact, the masses of the proton, neutron, and
  electron are as follows...
• Proton 1.0078252 amu
• Neutron 1.0086654 amu
• Electron 0.0005486 amu
• But you only need to know these values to the
  nearest whole number.
• Proton 1 amu
• Neutron 1 amu
• Electron 0 amu

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Isotopes and the Atomic Mass Unit

• The mass number of the isotope is ONLY the
  approximate mass of the nuclide.

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Isotopes and the Atomic Mass Unit

• Why is C-12 the only isotope whose mass number is
  exactly equal to its actual mass?

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Isotopes and the Atomic Mass Unit

• What is an Atomic Mass Unit (amu)?
• The Atomic Mass Unit (amu) is a very, very,
• very small amount of mass that is equal to
• 0.000,000,000,000,000,000,000,001,660,54 g.
• The isotope C-12 has been chosen as the
• standard for the Atomic Mass Unit (amu).
• An atom of the isotope C-12 has been given
• the mass of 12.00000000000000000000 amu.
• Thus... 1 amu 1/12 the mass of a C-12 atom.

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Isotopes and the Atomic Mass Unit

• That is why C-12 the only isotope whose mass
  number is exactly equal to its mass?

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Isotopes and the Atomic Mass Unit

• One gram (1 g) would equal to ...
• 602,000,000,000,000,000,000,000 amu
• One ounce (1 oz) would equal to ...
• 17,100,000,000,000,000,000,000,000 amu
• One pound (1 lb) would equal to ...
• 273,000,000,000,000,000,000,000,000 amu

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Isotopes and the Atomic Mass Unit

• To give you an idea of the scale of the amu ...
• if the big bang occurred 15 billion years ago,
  then that was...
• 5,475,000,000,000 days ago ... ,
• 131,400,000,000,000, hours ago ... ,
• 788,400,000,000,000, minutes ago ... ,
• 473,000,000,000,000,000 seconds ago.
• One gram (1 g) would equal to ...
• 602,000,000,000,000,000,000,000 amu.

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Isotopes and the Atomic Mass Unit

• Consider an atom with following composition
• 20 protons and 17 neutrons
• The atomic number of the atom is _____.
• The mass number of the atom is_____.
• The name of the atoms isotope is _____________.
• The nuclide symbol for the atom is...
• The approximate mass of the atom is _____ amu.

20
37
calcium-37
37