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Physical Data

Physical Data:

PHYSICAL DATA
Melting Point:	- 259.2°C
Density (gas):	0.08985 g/liter
Density (liq):	0.071g/cc
Solubility(@25C):	1.8 vol./100vol. water
Critical Temperature:	- 241°C
Critical Pressure:	20 atm.
Heat of vaporization:	218 cal/mole
Heat of dissociation (H2):	103,730 cal/mole

HYDROGEN FACTOIDS

Atomic hydrogen combines to form the molecule H₂, normally found in nature.

The gas is odorless, and tasteless. Free hydrogen constitutes only about 1% of the earth's crust, but if we include the hydrogen mated to other molecules, the proportion increases to 16% of all atoms on the earth's surface. Hydrogen makes up about 30% of the mass of stars.
Discovered 1783 by Cavendish, who in his experiments with "dephlogisticated air" produced a clear liquid - water. It took Lavoisier to recognize the significance of the experiment and to coin the word hydrogen. It was not until 1898 that Dewar succeeded to liquefy hydrogen gas.
Due to the spin of protons two forms exist, ortho- with both protons spinning the same; para- with protons of opposite spin. At room temperature the gas is 1/4 para, at boiling point it is almost pure para. The boiling point of pure para is 20.25K(-252.75C).

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