CHEMISTRY

Qualities vs. Quantities

· Chemical properties seem qualitative

· “virtues,” “active principles” (Newton)

· The new science required quantities

· Matter and motion

Phlogiston Theory A good overview of the whole topic

J. J. Becher

Georg Ernest Stahl

· 1660-1734

· phlogiston – the fire principle

Phlogiston’s properties

· Released when wood burns, metals calcify and rust

· Produces heat when escaping

· Found in organic matter

· Metal calces could be re-impregnated with phlogiston

· Plants absorb phlogiston

· Combustion impossible in a vacuum

Phlogiston’s problem

· Calces weigh more than original metal

· Ad hoc explanation: phlogiston possesses levity (lighter than nothing)

Gases

· Van Helmont (1597-1644)

· The name “gas” from the Greek caoV, from which we get “chaos” in English

· Stephen Hales’ Pneumatic Trough to collect gases in a chemical reaction (liberated “airs”)

New gases discovered

· Joseph Black (1728-1799)

· “Fixed Air” (CO₂)

· Quantity of Heat (as opposed to temperature)

· Specific Heat

· Latent Heat

The Discovery of Oxygen

Joseph Priestley (1733-1804)

Antoine Lavosier (1743-1794)

THE ELEMENTS, ATOMS AND THE PERIODIC TABLE

John Dalton

n Multiple proportions reveal discrete units

n E.g. multiple proportions of oxygen and carbon (CO and CO₂)

n Amadeo Avogadro

n Volumes of gases in compounds

n A given volume of gas contains a fixed number of molecules

n E.g. Water = 2 vols of hydrogen and 1 of oxygen à H₂O

Dmitri Ivanovich Mendeleev (1834-1907)

n Mendeleev notes groups of atoms

n All in Group I form compounds with oxygen in 2:1 ratio

n All in Group II form compounds with oxygen in 1:1 ratio

n Gaps in periodic sequence

n Mendeleev predicts element he called eka-Aluminum

n Later discovered, named Gallium, in 1874

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