Helium

The first evidence of helium (He) was observed in 1868 by the French astronomer Jules Janssen, who observed an unknown yellow line in the spectrum of sunlight during a solar eclipse. Later in the same year, the English astronomer Norman Lockyer observed the same yellow line and concluded that it was caused by an element in the sun that was unknown on Earth. Lockyer and the English chemist Edward Frankland named this new element 'helium', from the Greek helios meaning sun. Helium wasn't isolated on Earth until 1895, when William Ramsay treated cleveite, a uranium-containing mineral, with acids. The Swedish chemists Per Teodor Cleve and Abraham Langlet isolated helium independently by the same method and in the same year. Helium is the only element to be discovered extraterrestrially before being found on Earth.

Helium is the first of the noble gases and is chemically inert under normal conditions, although unstable compounds such as HeNe, HgHe₁₀ and WHe₂ have been created using an electric glow discharge. Helium has the lowest melting and boiling points of all the elements, and except under extreme conditions, it is always observed as a monatomic gas.

One of helium's more amusing properties is the effect it has on the voice. Helium is less dense than air, and so sound waves travel faster in helium than in air. As the fundamental frequency of a gas-filled cavity is proportional to the speed of sound in the gas, inhaling helium causes the resonant frequencies of the vocal tract to increase in pitch, resulting in a higher voice. The opposite effect can be achieved by inhaling a gas that is more dense than air, for example sulphur hexafluoride. Be careful playing with gases though, as both helium and sulphur hexafluoride are asphyxiants.

The largest use of helium is as a cryogenic fluid for temperatures at or below 4.2 K. This mostly involves cooling the superconducting magnets in MRI scanners. Helium is also used as a lifting gas for balloons and airships, as it is lighter than air and, unlike hydrogen, is non-flammable.

Hydrogen

The discovery of hydrogen (H) is usually credited to Henry Cavendish, who, in 1766, named the gas produced in the reaction between a metal and an acid 'flammable air'. In 1781, Cavendish also observed that this gas burned in oxygen to form water. Antoine Lavoisier reproduced this finding in 1783, and named the gas 'hydrogen', from the Greek hydro meaning water and genes meaning creator.
 
Hydrogen is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms. Throughout the universe, it is usually found in its atomic or plasma forms, unlike on Earth, where it is always observed as a diatomic gas with formula H₂.

Hydrogen's ability to burn in air provided us with the famous 'squeaky pop' test, a favourite of Chemistry lessons everywhere. If hydrogen is produced in a reaction and a burning splint is placed near the gas, a loud 'pop!' will be heard. This sound is caused by the gas igniting.
 
Due to its low density, hydrogen was once widely used as a lifting gas for balloons and airships. This practice stopped after the 1937 Hindenburg disaster, in which the German airship LZ 129 Hindenburg caught fire and was destroyed during a landing attempt. 36 people were killed. Helium has now taken over as the lifting gas of choice, as, although it is heavier than hydrogen, it has the advantage of being non-flammable.
 
The most common modern uses of hydrogen are in the processing of fossil fuels and in the production of ammonia, an important ingredient of fertilisers. It is also used as a coolant for electrical generators at power stations, as it has the highest thermal conductivity of any gas. Liquid hydrogen is used as a rocket fuel in the space programme. Another use of hydrogen is as an energy carrier, as, unlike fossil fuels, it does not release CO₂ on burning. However, due to costs and difficulties with hydrogen storage, currently it isn't widely used.

A change of focus

I've decided to change the focus of my blog this year, mainly because Zintl ions, fascinating as they are, are a bit of a niche topic. There just aren't enough developments in this area of Chemistry for me to be able to write about it regularly, as shown by the pathetic number of posts for 2012. I will therefore go back to basics a bit and start writing about the elements. I will aim to write one post about each element on a fairly regular basis. The advantage of this is that I shouldn't run out of things to write about for a long time! Plus maybe I'll be able to provide some fascinating but little-known facts about the elements! Maybe... I'll be starting with hydrogen very soon, so watch this space!