Helium does not burn except under very extreme circumstances.
Helium is a noble gas and therefore its molecular form is a single atom. A low energy atom of helium contains two protons, two neutrons, and two electrons. By comparison, the hydrogen atom contains one proton, one neutron, and one electron and cannot be burned either; however, the gaseous form of hydrogen is a two atom molecule (H2) with drastically different chemical characteristics. When combined with an oxidizer like oxygen (O2) and a source of heat, H2 will readily combust, producing energy in the form of heat and the byproduct water. Helium cannot be burned because the molecular state of helium gas is a single atom, which is stable in the presence of an oxidizer like oxygen. [“Technical data” Periodictable.com]
Tricking Helium into Burning
A team of physicists led by Donald Fleming recently reported tricking a helium atom into behaving like a hydrogen atom, thereby changing its chemical characteristics enough so that it could be burned. To perform this trick, they smashed a beam of muons into a cloud of helium, hydrogen, and ammonia gas using an accelerator. Since the muon is heavier than an electron, it sits two hundred times closer to the nucleus. At this position, it canceled out one of the positive charges of a proton, resulting in the remaining electron orbiting the nucleus with only one positive charge like that of the hydrogen atom, thus changing its chemical characteristics. The new molecule is then susceptible to an oxidizer like oxygen and can be burned. Due to its higher mass, it burns more slowly. [“Atomic disguise makes helium look like hydrogen” New Scientist]
Solar Burning of Helium
In about 5 billion years, the sun will begin to form a red giant and heat up. When the core reaches about one hundred million degrees, the helium will begin to burn. However, rather than forming a new molecule, three helium atoms will combine to form carbon-12. Until then, the helium in the sun will continue to produce ultraviolet light due to its ionization at 60,000º C. [“Helium Burning.” Cornell Astronomy]
“Technical data for the element Helium in the Periodic Table.” The Photographic Periodic Table of the Elements. N.p., n.d. Web. 2 Jan. 2013. http://periodictable.com/Elements/002/data.html.
“Technical data for the element Hydrogen in the Periodic Table.” The Photographic Periodic Table of the Elements. N.p., n.d. Web. 2 Jan. 2013. http://periodictable.com/Elements/001/data.html.
“Atomic disguise makes helium look like hydrogen – physics-math – 28 January 2011 – New Scientist.” Science news and science jobs from New Scientist – New Scientist. N.p., n.d. Web. 7 Jan. 2013. <http://www.newscientist.com/article/dn20049-atomic-disguise-makes-helium-look-like-hydrogen.html>.
“Helium Burning.” Cornell Astronomy. N.p., n.d. Web. 2 Jan. 2013. http://www.astro.cornell.edu/academics/courses/astro201/helium_burn.htm.
“Helium.” Periodic Table of Elements and Chemistry. N.p., n.d. Web. 7 Jan. 2013. http://www.chemicool.com/elements/helium.html