[Chemistry Class Notes] Helium Pdf for Exam

What is Helium?

Helium is the lightest noble gas that has been detected and is the only element of the Helium periodic table and was discovered by the French astronomer Pierre Janssen, who also detected a bright yellow line in the solar chromosphere spectrum during an eclipse in 1868. The helium element can be found on the top right side of the periodic table, and the atomic number of helium is 2, where it comes first amongst the noble gases family.

It held a single atomic orbital and was named by Frankland and Lockyer. The term helium is derived from the Greek word “Helios,” which means Sun. Before it was discovered, scientists knew there was an enormous amount of helium in the Sun.

Since its outermost electron orbital is full with two electrons, helium falls under inert gas. Also, helium can be found in compressed air tanks, lasers, and as a coolant in nuclear reactors. Helium holds the lowest melting and boiling points among all the other elements. The Nuclear fusion of hydrogen in stars generates helium in a significant amount.

The Helium symbol is  He.

Abundance of Helium

Helium is the second lightest and most abundant element in the universe, which is observable (where hydrogen is the most abundant and lightest). It exists about 24% of the total elemental mass, which is more than 12 times the mass of all the combined heavier elements. In both the Sun and in Jupiter, its abundance is similar to the same.

This is because of the very high nuclear binding energy (per nucleon) of helium-4, concerning the next three elements after helium. Also, Helium-4 binding energy is accountable for why it is a product of both radioactive decay and nuclear fusion. The most amount of helium in the universe is helium-4, the huge majority of which was formed at the time of the Big Bang. Excess amounts of new helium are being created by the nuclear fusion of hydrogen in stars.

The abundance of helium-3 and helium-4 is equivalent to 0.0002% and 99.9998%, respectively. This difference in abundances can be seen in the Earth’s atmosphere, where the ratio of 4He atoms to 3He atoms is nearly 1000000:1.

Isotopes of Helium

Although there are eight isotopes of helium (He) (standard atomic mass: 4.002602(2) u), which are known, from those, only helium-3 (3He) and helium-4 (4He) are stable. All the radioisotopes are short-lived, and the longest-lived is being 6He, with a half-life of

806.7 milliseconds. The least stable is 5He, with a half-life of 7.6×10−22 seconds, even though it is possible that 2He has a shorter half-life ever.

There is one 3He atom for every million 4He atoms in the Earth’s atmosphere. However, helium is an unusual element in that its isotopic abundance varies highly based on its origin. The proportion of 3He is up to a hundred times higher in the interstellar medium. Different formation processes of two stable isotopes of the helium produce different isotope abundances.

Properties of Helium

The helium element is an odorless, colourless, insipid, and non-toxic, gas. Other than any has, it is less soluble in water. It is also the less reactive element and doesn’t form chemical compounds essentially. The viscosity and density of helium vapour are very low. The thermal conductivity and the caloric content of helium are exceptionally high. Helium can be liquefied, but its condensation temperature is the lowest when compared to all the known substances. The physical and chemical properties of Helium gas are given below briefly.

The physical properties of helium are nothing but the characteristics that are seen without changing the substance into another. The physical properties of helium are tabulated below.

Physical Properties of Helium

Chemical Properties of Helium

Chemical properties are simply the characteristics that define how the element reacts with other substances or changes from one to another substance. And, the chemical properties are seen only during a chemical reaction.

The Chemical Properties of Helium are Tabulated Below.

Health Effects of Helium

Humans have no sense that they can detect the presence of Helium. Although Helium is non-toxic and inert, it can act as a simple asphyxiant by displacing oxygen in the air to the below-required levels to support life. Excessive inhalation of Helium can cause dizziness, nausea, vomiting, loss of consciousness, and death.

Death may result from confusion, errors in judgment, loss of consciousness that prevents self-rescue. At low concentrations of oxygen, unconsciousness and death may occur in seconds without any warning. Personnel, including rescue workers, should not enter areas where the concentration of oxygen is lower to 19.5% unless offered with a self-contained breathing apparatus or an air-line respirator.