The Atom

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The Atom
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Two major parts of an atom
Nucleus (not to scale)
Electron Cloud
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Three Major Sub-Atomic Particles

• Protons
• Neutrons
• Electrons

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THE PROTON

• Heavy 1 amu
• Positive 1 charge
• Location Nucleus

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THE NEUTRON

• Heavy 1 amu
• No charge, neutral
• Location Nucleus

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THE ELECTRON

• Very light 1/2000 amu
• Negative ? -1 charge
• Location electron cloud

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Where are they located?
Nucleus Protons and Neutrons
Electron Cloud Only Electrons
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ATOMIC NUMBER (Z)

• The of protons in an atom
• Can not change for an element
• All atoms are neutral, so Z equals the of
  electrons
• For an ion the number of electrons may differ

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Example Sodium
Atomic of protons
11
Na
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MASS NUMBER (A)

• The mass of an atom
• A protons neutrons
• To determine of neutrons
• Neutrons A - Z

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Example

• An atom of sodium has a mass of 24 amu, how many
  protons, electrons and neutrons does it have?

11 p 11 e- 24 - 11 13 N
11
Na
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ISOTOPES

• Atoms of the same element that differ in
  mass.(They have the same of p, but different
  of N)

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Isotope Notation
Mass
Atomic
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Isotope Notation

• Can also be written as ELEMENT MASS
• Example Carbon - 12

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So, why do the elements on the PT have masses
with decimals???
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AVERAGE ATOMIC MASS

• The weighted average mass of all naturally
  occurring isotopes of an element.

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Example using exam scores!
Exam Scores can be weighted higher than homework
or quiz grades What if And you
received Exam 50 Exam 93 Quizzes
20 Quizzes 82.5 Homework 30 Homework
85 Your grade (93 x .5) (82.5 x .2)
(85 x .3) 88.5
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Example

• Example The element hydrogen has three
  isotopes. It exists in nature 99.41 of the time
  as Hydrogen-1, 0.4 of the time as Hydrogen-2 and
  0.19 of the time as Hydrogen 3. What is the
  average atomic mass of hydrogen?
• 0.99951 0.0042 0.0013 1.0078 u

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Famous Scientists in Atomic Theory
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Democritus (400 B.C.)

• First to develop the idea of an atom.

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DALTON

• Dalton created an atomic theory that stated
• All elements are composed of tiny indivisible
  particles called atoms
• Atoms of the same element are identical. The
  atoms of any one element are different from those
  of any other element

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J.J. Thomson

• Plum Pudding Model
• Solid positively charged sphere
• Electrons embedded within

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Rutherfords Gold Foil Experiment
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Rutherford

• Proved the existence of a tiny, dense, positively
  charged nucleus.
• The rest of the atom is mostly empty space.