2) Element symbol: He
 

3) Number of electrons, protons, and neutrons: 2 electron, 2 proton, 2 neutrons
 

4) Atomic number: 2
 

5) Atomic mass: 4.00260
 

6) Characteristics:

At ordinary temperatures it is a colorless and odorless gas.
 

7)

History:

The French astronomer Pierre Janssen (1824-1907) discovered helium in the spectrum of the corona of the sun during an eclipse in 1868. Shortly afterward it was identified as an element and named by the British chemist Sir Edward Frankland and the British astronomer Sir Joseph Norman Lockyer.

Three things made from the element:

- used in inert-gas-arc welding for light metals such as aluminum and magnesium alloys that might otherwise oxidize/ The helium protects heated parts from attack by air.

- in surgery, beams of ionized helium from synchrocyclotron sources are proving useful in treating eye tumors, by stabilizing or even shrinking the tumors.

- used in place of nitrogen as part of the synthetic atmosphere breathed to relive sufferers of respiratory difficulties because helium moves more easily than nitrogen through constricted respiratory passages.
 

8) Isotopes:

At temperatures slightly above absolute zero, liquid helium is transformed into helium II, also called superfluid helium. It has no freezing point, and its viscosity is apparently zero. It has 2 electrons, 2 protons, and 2 neutrons having a total mass of 4.

Helium-3 has a mass of 5, having 3 neutrons. It has an even lower boiling point than ordinary helium. About 1 part per million of atmospheric helium consists of helium-3, now thought to be the product of the decay of tririum, a radioactive hydrogen isotope with a mass of 3.

Helium-4 is the most common helium isotope. It probably comes from radioactive alpha emitter in rocks.
 

9) Helium, like other noble gasses is chemically inert. Its single electron shell is filled, making possible reactions with other elements extremely difficult and the resulting compound quite unstable. Molecules of compounds with neon, another noble gas, and with hydrogen have been detected, however, and other compounds have been suggested.
 

10) Helium solidifies at -272.2 °C (-457.9 °F) at pressures above 19,000 torr (25 atm) and boils at -268 °C (-452.0 °F).