Atomic Structure

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Atomic Structure
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What Is An Atom?

• the smallest particle of an element that retains
  the chemical properties of that element
• Can be subdivided into electrons (e-), protons
  (p) and neutrons (n0)

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Diagram Of An Atom
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Important Info About Subatomic Particles
Particle Relative Electric Charge Mass Number Relative Mass (amu) Actual Mass (kg)
Electron (e-) -1 0 .0005486 9.109 x 10-31
Proton (p) 1 1 1.007276 1.673 x 10-27
Neutron (no) 0 1 1.008665 1.675 x 10-27
1 amu (1/12)(mass of C-12 isotope in kg)
1 amu 1.660540 x 10-27 kg
Amu atomic mass units
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Atomic Number (Z)

• Tells us the number of protons in the nucleus of
  an atom

Z
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Isotopes

• Some atoms of the same element will have
  different masses.
• These atoms are called isotopes because they have
  the same number of protons, but differ in the
  number of neutrons.
• Isotopes of the same element have different mass
  numbers.
• Mass number (A) is the total number of protons
  and neutrons in the nucleus of an isotope

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How Are Isotope Symbols Denoted?
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Hyphen Notation of Isotopes

• Isotopes can also be denoted through hyphen
  notation
• The element symbol will be listed, following a
  hyphen, and then a mass number (p n0)
• Ex. Hydrogen has 3 isotopes (H-1, H-2, H-3)

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Hydrogen Isotopes
AKA Protium 99.985 Abundant H-1
.015 Abundant H-2
Radioactive, Prepared Artifically H-3
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Sample Problems

• How many protons, electrons, and neutrons are
  there in a Cl-37 atom?
• How many protons, electrons, and neutrons are
  there in the following isotopes?

-1
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Atomic Mass

• What is the atomic mass listed on the periodic
  table under each element really measuring?
• This mass is a weighted average of all of the
  naturally occurring isotopes of an element
• This mass is a relative average (compared to the
  C-12 isotope) in atomic mass units (amu)

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How To Find The Atomic Mass of Hydrogen

• H-1 is 99.985 abundant with an atomic mass of
  1.007825 amu
• H-2 is .015 abundant with an atomic mass of
  2.016490 amu
• H-3 is not counted because of the fact that it is
  not naturally occurring
• To find the weighted average
• ( abundance/100)(relative atomic mass of isotope
  1)
• ( abundance/100)(relative atomic mass of isotope
  2)
• ( abundance/100)(relative atomic mass of isotope
  3)
• Mass may be substituted for the relative
  atomic mass when given
• (99.985/100)(1.007825 amu) (.015/100)(2.016940
  amu)
• 1.0079 amu

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Things To Remember

• If you change the number of protons, you change
  the type of atom itself.
• If you change the number of electrons, you change
  the atom to an ion (charged particle).
• If you change the number of neutrons, you change
  the isotope of that element.