Isotopes

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Isotopes

• Atoms of the same element with different mass
  numbers.

• Nuclear symbol

• Hyphen notation carbon-12

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ationsarts/pages/chem
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Isotopes
Electrons
Nucleus
Electrons
Neutrons 6 Protons 6 Electrons 6
Neutrons 8 Protons 6 Electrons 6
Nucleus
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Isotopes

• Chlorine-37
• atomic
• mass
• of protons
• of electrons
• of neutrons

• 17
• 37
• 17
• 17
• 20

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ationsarts/pages/chem
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Relative Atomic Mass

• 12C atom 1.992 10-23 g

• atomic mass unit (amu)
• 1 amu 1/12 the mass of a 12C atom

Neutron

• 1 p 1.007276 amu1 n 1.008665 amu1 e-
  0.0005486 amu

Electrons
Nucleus
Proton
Nucleus
Carbon-12
Neutrons 6 Protons 6 Electrons 6
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Average Atomic Mass

• weighted average of all isotopes
• on the Periodic Table
• round to 2 decimal places

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ationsarts/pages/chem
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Average Atomic Mass

• EX Calculate the avg. atomic mass of oxygen if
  its abundance in nature is 99.76 16O, 0.04 17O,
  and 0.20 18O.

16.00 amu
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ationsarts/pages/chem
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Average Atomic Mass

• EX Find chlorines average atomic mass
  if approximately 8 of every 10 atoms are
  chlorine-35 and 2 are chlorine-37.

35.40 amu
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ationsarts/pages/chem
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Isotopes

• Dalton was wrong.
• Atoms of the same element can have different
  numbers of neutrons
• different mass numbers
• called isotopes

C-12 vs. C-14
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Naming Isotopes

• Put the mass number after the name of the element
• carbon- 12
• carbon -14
• uranium-235

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Atomic Number and Mass Number
Atomic Number and Mass Number
Atomic Number and Mass Number
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Ions and Subatomic Particles
Ions and Subatomic Particles
Ions and Subatomic Particles
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Atomic Mass

• How heavy is an atom of oxygen?
• There are different kinds of oxygen atoms.
• More concerned with average atomic mass.
• Based on abundance of each element in nature.
• Dont use grams because the numbers would be too
  small

California WEB
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Measuring Atomic Mass

• Unit is the Atomic Mass Unit (amu)
• One twelfth the mass of a carbon-12 atom.
• Each isotope has its own atomic mass we need the
  average from percent abundance.

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Calculating averages

• You have five rocks, four with a mass of 50 g,
  and one with a mass of 60 g. What is the average
  mass of the rocks?
• Total mass (4 x 50) (1 x 60) 260 g
• Average mass (4 x 50) (1 x 60) 260 g
  5 5
• Average mass 4 x 50 1 x 60 260 g
  5 5 5

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Calculating averages

• Average mass 4 x 50 1 x 60 260 g 5
  5 5
• Average mass .8 x 50 .2 x 60
• 80 of the rocks were 50 grams
• 20 of the rocks were 60 grams
• Average as decimal x mass as
  decimal x mass as decimal x mass

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Atomic Mass

• Calculate the atomic mass of copper if copper has
  two isotopes. 69.1 has a mass of 62.93 amu and
  the rest has a mass of 64.93 amu.

California WEB
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Isotopes

• Because of the existence of isotopes, the mass of
  a collection of atoms has an average value.
• Average mass ATOMIC WEIGHT
• Boron is 20 B-10 and 80 B-11.
  That is, B-11 is 80 percent abundant on
  earth.
• For boron atomic weight
• 0.20 (10 amu) 0.80 (11 amu) 10.8 amu

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Periodic Table

• Dmitri Mendeleev developed the modern periodic
  table.
• Argued that element properties are periodic
  functions of their atomic weights.
• We now know that element properties are
  periodic functions of their
  ATOMIC NUMBERS.

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Atomic Mass

• Magnesium has three isotopes. 78.99 magnesium 24
  with a mass of 23.9850 amu, 10.00 magnesium 25
  with a mass of 24.9858 amu, and the rest
  magnesium 26 with a mass of 25.9826 amu. What is
  the atomic mass of magnesium?
• If not told otherwise,
• the mass of the isotope is the mass number
  in amu.

24.304 amu
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Atomic Mass

• Calculate the atomic mass of copper if copper has
  two isotopes. 69.1 has a mass of 62.93 amu and
  the rest has a mass of 64.93 amu.

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• B. C.
• D. E. F.
• G. H. I.

Given the average atomic mass of an element is
118.21 amu and it has three isotopes (A, B,
and C) isotope A has a mass of 117.93 amu
and is 87.14 abundant isotope B has a mass
of 120.12 amu and is 12.36 abundant Find the
mass of isotope C. Show work for credit.
Extra Credit What is a cation?
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Given the average atomic mass of an element is
118.21 amu and it has three isotopes (A, B,
and C) isotope A has a mass of 117.93 amu
and is 87.14 abundant isotope B has a mass
of 120.12 amu and is 12.36 abundant Find the
mass of isotope C. Show work for credit.
119.7932 amu
Extra Credit What is a cation?
A positively charged atom. An atom that has lost
a(n) electron(s).
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Given the average atomic mass of an element is
118.21 amu and it has three isotopes (A, B,
and C) isotope A has a mass of 117.93 amu
and is 87.14 abundant isotope B has a mass
of 120.12 amu and is 12.36 abundant Find the
mass of isotope C. Show work for credit.
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Isotopes
Isotopes Lab
Isotopes Lab