The Atomic Nature of Matter

Summary

Ordinary matter (as opposed to dark matter) is mostly composed of atoms.
Atoms …
- are discrete entities.
  - A discrete system is composed of distinct individual parts. A discrete system is separable into pieces.
  - The opposite of discrete is continuous. A continuous system forms an unbroken whole without interruption. One region blends seamlessly into another.
- can only be found in a limited number of basic types called elements (short for chemical elements).
  - There are 90 naturally occurring elements found on earth.
  - An additional 28 elements have been produced artificially in laboratories on earth.
  - A few elements that exist on earth only in the laboratory have been detected in stars other than the sun.
- can be stable or unstable.
  - Unstable atoms have a finite lifetime.
    - There is a statistical probability that an unstable atom will decay into an atom of a different element.
  - Stable atoms are eternal.
    - The stable atoms of everyday existence are several billion years old.
      - Nearly all of the hydrogen and helium in the universe was created in the first three minutes of the universe's existence (13.8 billion years ago).
      - Nearly all of the elements heavier than helium found on the earth were created many millions of years before the solar system formed (4.5 billion years ago).
    - Stable atoms can be used over and over again (recycled) in different combinations and will never "wear out".
- can be "seen" only with great difficulty.
  - Atoms are effectively "invisible".
    - Atoms are on the order of 10⁻¹⁰ m in size.
    - Light waves are on the order of 10⁻⁶ m in size.
    - Since light is 10,000 times larger than atoms, atoms are too small to be "seen" with light. (No optical device can ever be used to image atoms.)
  - Atoms can be inferred to exist through …
    - the chemical laws of definite and multiple proportions.
    - the physical laws of statistical thermodynamics.
  - Atoms can be imaged through …
    - x‑ray diffraction
    - scanning tunneling electron microscopy
    - atomic force microscopy
Atoms can combine to form …
- ionic solids
- network solids
- metallic solids
- molecules

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