The Atom

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The Atom

• Background for Lessons on the Periodic Table of
  the Elements

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The Atom

• Every element is made of atoms
• All atoms of any element are the same
• Atoms of different elements are different

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Atomic Number-Atomic Mass
Atomic Number Protons in Nucleus
Atomic Mass Sum of Masses of Protons
Neutrons (e.g., 207.2 g/mol)
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Periodic Pattern
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Thomson Model The Electron
J.J. Thomson discovered electrons using an
experimental device similar to your TV---over 100
years ago! He deduced the electrons must be from
atoms, and there must be other, more massive
particles in the atom.
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Rutherfords Atom Model

• Mostly empty space
• Small dense region-nucleus
• Protons are part of nucleus
• Hypothesized a third, neutral particle existed
• Neutron discovered later by Chadwick

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Bohrs Atom Quantum Mechanics
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Quantum Model
Today, the quantum model is the most realistic
vision of the overall structure of the atom. It
explains much of what we know about chemistry and
physics including why elements are ordered by
atomic number in the Periodic Table.
How Atoms Work by Craig C. Freudenrich, Ph.D.
from http//science.howstuffworks.com/atom1.htm
9-15-05
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See the Atom
Photo courtesy NISTPhoto source IBM's Almaden
Research LabsAtoms can be positioned on a
surface using the STM tip, creating a custom
pattern on the surface.