General Chemistry Paper on Chemical Elements: Helium
Rabun Gap-Nacochee School
Helium is an element in the periodic table. It has the symbol He and an atomic number of 2. Its average atomic mass is about 4.002602 u. There are 7 known isoptopes of helium, bearing the electron configuration 1s2. The ionic radius of this element is 93 pm. Helium was first observed and found by French astronomer Pierre Jules César Janssen along with the scientist Joseph Norman Lockyer in 1868, adding one more element to the periodic table.
The usual phase of helium is gas. At zero degree Celsius, under the pressure of 101.325 kPa, the density of helium is approximately 0.1786 g/L. At its boiling point, the liquid density of helium is 0.125g/mL. In natural conditions, helium has no color and no smell. As people can do some fun experiments by breathing in helium, it's true to say that helium is a non-toxic gas. However, inhaling helium can be dangerous if done in excessive amount, since helium is an asphyxiant which displaces the normal oxygen concentration. Like other noble gases, helium is an inert element, meaning that it has very low chemical reactivity in natural conditions. Helium doesn't react with any other elements. It has the lowest boiling (4.216 Kelvin degree) and melting (0.95 Kelvin degree) points among all elements in the periodic table.
Helium's physical properties is very unusual. It exists only as a gas, except in some really extreme conditions. In liquid form, it is the only liquid that cannot be solidified by lowering the temperature. When helium is cooled down to about 4 degrees above absolute zero, it becomes liquid. When we keep lowering the temperature a couple of degrees colder, it becomes a superfluid that flows without resistance from its container. At the pressure of about 50 atm and a very low temperature of about 0.2 above absolute zero, it changes into a special state. Whether it's a supersolid, a solid with some fluid moving...
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