How Atoms Differ Notes

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How Atoms Differ Notes
Section 4.3 Notes
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What makes one atom, like hydrogen, different
from another atom like helium?

• The number of protons located in the nucleus!!!!!!

What element is this?
Oxygen b/c it has 8 p
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• The atomic number is the number of protons in an
  atom.
• atomic number p
• On the periodic table, elements are arranged
  according to increasing atomic number.

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Periodic Table
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atomic number
1 p
atomic number
2 p
atomic number
3 p
atomic number proton
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• Remember Atoms are
• electrically NEUTRAL
• b/c they have the
• SAME number of protons and
• electrons!!!! p e-

p
e-

atomic number
atomic number p e-
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atomic number
1 p
1 e-
atomic number
2 p
2 e-
atomic number
3 p
3 e-
atomic number proton electron
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What element is represented by atom 1? What
about atom 2?
So whats the difference in the atoms?
Lithium (Li)
Lithium (Li)
1
2
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Mass Number

• The mass number is the
• number of protons
• PLUS the number of
• neutrons

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• The mass number is NOT on the periodic table!!!

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• The mass of the atom is
• mainly inside the nucleus!
• (where the p and n0 are)

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atomic number 6
C
mass number 12
protons 6
electrons 6
neutrons 6
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atomic number 6
C
mass number 13
protons 6
electrons 6
neutrons 7
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atomic number 6
mass number 14
C
protons 6
electrons 6
neutrons 8
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Subatomic particles
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Isotopes

• Isotopes are atoms of the same element with the
  same number of protons, but DIFFERENT NUMBERS OF
  NEUTRONS

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Isotopic Notation
mass number
symbol
atomic number
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example
mass number
Ne
atomic number
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Isotopic Name
element name mass number
Neon 22
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