Atomic Number

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Atomic Number

• The number of protons in an atom
• Also, the number of electrons in a neutral atom

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• atomic number atomic number atomic number
• 1
  6 79

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Atomic Mass

• The number of protons neutrons in the nucleus
• Since the mass of an electron is soooo much
  smaller than the mass of protons or neutrons, we
  do not include it in the atomic mass

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Showing atomic number and mass

• 7 Li
  3
• 3 protons
• 3 electrons
• 7-3 4 neutrons

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• How many protons, neutrons, electrons?

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Ion

• An atom that has gained an electron is called an
  anion. It has a net negative charge.
• An atom that has lost an electron is called a
  cation. It has a net positive charge.

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Isotope

• Atoms of the same element that have different
  atomic masses (but same atomic number)
• WHY
• do they have different atomic masses?

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Isotope

• If two atoms are of same element, they MUST have
  the same number of protons (the same atomic
  number)
• But. they can have different number of NEUTRONS.
  The more neutrons, the heavier the atom

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Hydrogen

• Hydrogen is the smallest atom.
• Most hydrogen atoms have only one proton and one
  electron (no neutrons)
• 1H
• 1

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One isotope of Hydrogen has a neutron
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Another isotopes of Hydrogen has 2 neutrons
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Isotopes of Hydrogen
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Isotopes of Lithium
3 neutrons
5 neutrons
4 neutrons
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Isotopes of carbon