Properties of Matter

Properties of Matter is the first lecture within the Properties of Matter section of PH1011. It covers a brief history of matter concepts, Dalton's atomic theory of matter, the mole and Avogadro's number.

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Next: Thermal Physics and Temperature

Historical Understandings of Matter
The Greeks are credited with the first concepts of matter as a scientific and understandable concept rather than a mere physical constant. Democritus put forth the theory that all matter was either atoms or empty space; Aristotle disagreed - believing instead that all things are a combination of the four "elements" of fire, water, earth and air. Unfortunately this proved to be the more popular theory and hobbled scientific endevour for the next few thousand years.

The concept of the atom was reiterated later (~1800) by Dalton, a chemist working with gases. Dalton recognised that elements react in simple proportions and that masses of constituents are conserved through reactions. These observations allowed Dalton to propose an atomic theory in which:
 * All matter is atoms
 * All atoms of one element are identical
 * Atoms can't be created, destroyed or separated into parts
 * Simple whole number ratio combinations of atoms allow for formation of compounds
 * Chemical reactions involve separation or combination of atoms.

This theory remains roughly correct if imperfect.

The Mole
The mole is defined as the number of atoms present in a 12g sample of carbon-12. Molar masses are the mass associated with one mole of a given substance, whether it be atoms or molecules or any other measurable quantity. Avogadro's number is the number of particles in a mole - 6.022x1023. The atomic mass unit or Dalton is = mass C12/12 = 1.66x10-27kg.


 * Example:
 * Given densityk = 862kgm-3, estimate the size of a potassium atom.
 * Molar mass K = 39g/mol
 * 1 square metre contains (862/0.039) 22102mol m-3
 * 22012 x NA = 1.3x1028 atoms m-3; each atom must take up 1/(1.3x1028) = 7.5x10-29 m3
 * Given this volume the length of each atom must be 3√(7.5x10-29 m3) = 4.2x10-10m

Summary
The Greeks were good for science. Amounts of substances can be expressed in moles, the mole being 6.022x10-23 molecules/atoms/ect. Knowing this value allows calculation of atomic sizes, alongside other varied applications in both physics and chemistry.