Atomic Structure and the Periodic Table Continued

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Atomic Structure and the Periodic Table Continued
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Atomic Mass

• Mass the amount of matter in an object
• What does an atom weigh?
• Unit of Measurement Atomic Mass Units or u
• 1u 1.67 X10-24 g
• or
• 0.00000000000000000000000167 g
• This is a REALLY SMALL NUMBER!!!!!

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Mass Number

• Mass Number the sum of the number of protons
  and neutrons in the nucleus of an atom
• Protons and Neutrons each have a mass around 1 u
• Example An atom has 6 protons and 6 neutrons
  What is the mass number?
• 6 protons 6 neutrons 12 u Carbon

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How Do You Know How Many Neutrons Are In An Atom

• Subtract the Atomic (which equals the of
  Protons) from the Atomic Mass
• Important Point Atomic weight and mass are not
  the same thing

Atomic Weight
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HUH!!!!!!

• To get the atomic mass from the atomic weight
  either round the atomic weight up or down (.0 -
  .49 round down .5 - .99 round up)
• Example Oxygen
• Atomic Weight 15.9994
• Atomic Mass 16

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Back to the original question

• For Oxygen the atomic mass is 16 and the number
  of protons is 8
• 16 atomic mass 8 Protons 8 Neutrons

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Do all atoms of the same element have the same
number of neutrons?

• No, they can be different
• Atoms of the same element that have different
  number of neutrons are called
• Isotopes!!!

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What does having different of neutrons mean for
the element?

• This means the different isotopes of the same
  element have different masses!!!!
• Average Atomic Mass
• The average mass of a mixture of its isotopes
• This is the number we find on the periodic table
  of elements