In Chapter 10 we will focus on gases and their properties. As an introduction to gases we can look at the periodic table and recall those elements which are found in the gas phase under standard conditions.

If we look at a periodic table which identifies the phase of each element at standard conditions we see that the dominate phase is solid followed by the gas phase and finally the liquid phase.

The elements which are gases include, hydrogen, helium, oxygen, nitrogen, fluorine, chlorine and all the noble gases. We'll take a few moments to look at several of these gaseous elements. I'll expect you to know the standard state phase of every element in the periodic table. Now you might be thinking, holy cow, are you nuts, but remember 2 of the elements are liquids and 10 of the elements are gases. So it is not so bad. Also I'll expect you to know the color of each of the gaseous elements.

Hydrogen is the most abundant element in the universe. Hydrogen is a colorless, odorless, tasteless gas. If boils at -252.8°ree;C and freezes at -259.1°ree;C. Hydrogen is obtained from water using a variety of chemical rxns.

Helium was the 1st noble gas to be discovered. It was identified on the sun before it was found on the earth. It discovery was made by a French astronomer Pierre Jules Casar Janssen in 1868. Helium is colorless, odorless, tasteless gas at room temperature. It boils as -268.6 °ree;C. It is the only element that cannot be converted to a solid by cooling alone. (Note later the pressure must be increased to 26 atmospheres before helium solidifies at -272 °ree;C.)

Oxygen, O2, is the most abundant element in the earths crust. O2 was discovered in the late 18th century by the English chemist Joseph Priestly. A colorless gas, at room temperature it condenses to a blue liquid at -183°ree;C and freezes to a pale blue solid at -218°ree;C. Obtained by the liquification of air.

Although nitrogen is the most abundant element in the atmosphere it is not particularly abundant on earth because there are few compounds containing nitrogen which are solids. Nitrogen is a colorless, odorless, tasteless gas. It boils at -196°ree;C and freezes at -210°ree;C. It is obtained from inpirification of air.

Fluorine is a pale yellow gas with a boiling point of –188 °ree;C. It freezes at –218 °ree;C. Fluorine is an extremely reactive gas and very difficult to work with in its a elemental state. I cannot show you a sample of fluorine beause of its reactivity. In fact, it is so reactive it even forms compounds with noble gas elements like xenon. We will talk about this interesting behavior later. Fluorine is commonly found in many minerals. (fluorspar, CaF2; cryolite, Na3AlF6 and fluorapatite, Ca3(PO4)3F).

Argon was identified by the physicist Lord Rayleigh and Sir William Ramsay. Their individual experiments identified the colorless, odorless, tasteless gas in 1894. It was the first nobel gas isolated on earth.

Later in 1898 Ramsay and an assistant Morris Travers isolated neon, from a sample of impure oxygen. They were also able to show that air contained two other element which they identified Krypton and Xenon.

Radon is obtained as a disintegration product of radium. It is a radioactive gas. Radon-222 decays by alpha particle emission to a variety of solid radioisatopes. Two of these isotopes are polorium-218 and polorium-214 which are also alpha emitted. As solids these remain in the lung. Radon, as a gas, is inhaled and then exhaled. Range of an alpha particle is very short.

Chlorine is a pale greenish–yellow gas, with a boiling point of –101 °ree;C and a melting point of –34 °ree;C. Chlorine is the most important of the halogens. (Look up some hazardous info on chlorine.)

Under appropriate conditions substances which are normally liquids or solids can exist in the gas phase. In such cases the gaseous phase of the substance is called vapor. For example, one of the two elements which exists as a liquid is bromine (show the periodic table). Here is a picture of bromine. Do you see the liquid phase of bromine? Do you see the vapor phase?