In the days of black and white photography, how can those who lived in the early part of the 20th century ever forget what happened on May 6th,1937? Today one can watch that video clip of the Hindenberg disaster that gripped the world then and is still quite dramatic and shocking to see now. The words of the reporter “Oh the humanity …..!” is something you cannot get out of your minds. This was a major tragedy that, if it had not occurred, would have changed the face of modern aviation completely.(Ref.1)
It was a chemistry blunder when hydrogen, a very inflammable gas was used to send the blimp with so many passengers up in the air. And it was not as if scientists did not know the easy burning of hydrogen. However, it was cheaper to use and had greater lift than Helium and was chosen since early test runs with the Hindenberg happened without any hitches.(Ref.2)
Hydrogen and Helium are both gases and are the only two elements on the first row of the Periodic Table. However, in spite of being gases, their properties could not be more different. Hydrogen,H, is the most abundant element in the universe, while Helium,He, is less than 0.0005%. H is very reactive and is hardly found as an element, whereas He is the first of the Noble inert gases and is not reactive.(Ref.3) The electronic structure gives us a hint; H is 1S1, whereas He is 1S2, which means the first s orbital is filled up and is a stable doublet.
Hydrogen is a colorless, odorless gas but is extremely reactive and forms myriads of compounds readily.
Let us delve into the differences of these two light gases.
Hydrogen is a gas and is the lightest element known. It is the only element with no neutrons and has 1 proton and 1 electron. However,it has two other isotopes, Deuterium that has a neutron and Tritium that has two neutrons. Hydrogen is not usually found in its elemental form on earth but is found as such in many planets especially Jupiter and is abundant in stars.(Ref.4)
Hydrogen has two oxidation states, +1 and -1. This makes it both an oxidizing and reducing agent. It is positively charged when reacting with halogens or oxygen and has a negative charge reacting with alkali metals.(Ref.4)
Helium, He, is also a colorless, odorless gas and has the second lowest atomic weight. Very little He is found in the earth’s atmosphere. Being such a light element, unconfined He immediately begins rising and escaping from the planet. However a lot of helium produced commercially is obtained from the ground. Some natural gas fields have enough helium mingled with the other gases to be extracted economically. Most of the helium recovered this way is thought to be formed as a result of radioactive decay of uranium and thorium found in granitoid rocks(See Activities for Middle School Teachers).(Ref.5)
Till World WarII, Helium was used in blimps, dirigibles, weather balloons or to fill balloons for parties and other festive occasions. Today it is used as a purging gas since it has the lowest melting and boiling point of any gas and is inert.(Ref.5) (A purging gas displaces other gases or liquids stored in tanks/containers.)
Since helium is an inert gas with low reactivity, high thermal conductivity and low density, it is an ideal gas to use in metallurgical processes, growing crystals in chemical vapors and manufacturing optical fibers, etc.(Ref.5)
Helium has very low atomic weight, high diffusion coefficient which means it escapes easily; hence it is used for leak detection. It is also used in breathing mixtures for deep water diving and medical procedures since it has a low viscosity and is easier to breathe under high pressure. A Helium atmosphere is good for welding processes since it does not react with the metals being welded.(Ref.5)
Hydrogen and Helium are both light gases; one electron and proton change causes such drastic differences in their properties and uses. One is present in almost everything but the other is hardly around us in the atmosphere. Yet both manage to play important roles in our lives.
Activities for Middle School Teachers:
Look at all the compounds in organic and inorganic chemistry that contain hydrogen. How many kinds of bonds are formed by a hydrogen atom? What classes of compounds in inorganic chemistry have to contain hydrogen? Are there compounds in organic chemistry that do not contain hydrogen? What is their number compared to those that do contain hydrogen?
Students can do a simple activity bringing everyday objects from home and figuring out if they contain the element hydrogen in them.
Look at the different kinds of rocks studied in geology. At least two types of rocks show the presence of helium. How are they formed in the earth? Where are they found on the earth?
Nuggets of Information:
Hydrogen, the lightest element of all, explodes at concentrations of 4-75%by volume in the presence of sunlight,flames or sparks.(Ref.4)
Despite being a stable element, hydrogen forms many bonds and exists in a wide variety of compounds. It is mostly found on earth as hydrocarbons and water.
The 3 isotopes of hydrogen show different properties because of the differing number of neutrons in the nucleus. Deuterium and its compounds are used in chemical experiments as well as in H-NMR Spectroscopy.(Ref.4)
In aqueous solutions the H+ ion is actually H3O+ or hydronium ion and this ion is extremely important in acid-base chemistry.(Ref.4)
The word ‘helium’ comes from the Greek word meaning sun (helios).(Ref.6)
The U.S. is the world’s largest supplier of helium, found in many natural gas fields.(Ref.6)
The balloon boy hoax on October 15, 2009 made people believe that a six-year old boy had floated away in a home-made helium balloon. But in reality, the boy was just hiding in his home.(Ref.6)
Since helium is less dense than air, when inhaled from a source, say, a helium balloon, it briefly changes the voice of the person to sound much higher. However, breathing too much helium could choke people due to lack of oxygen.(Ref.6)
Liquid helium is used for cooling metals in superconductivity experiments.(Ref.6)
Helium is a non-renewable source since the decay of thorium and uranium is slower than the rate at which it is being used. In 1925, the U.S. established a National Helium reserve and there was plenty of helium available. However, with more and more usage of helium as a purging gas and other uses and the selling of it to other countries, today we are at the stage that by 2021, the National Helium Reserve will be sold out.(Ref.5)
References:
1.https://www.youtube.com/watch?v=F54rqDh2mWA
2.http://www.answers.com/Q/Why_was_hydrogen_used_in_the_hindenburg
3.http://www.ehow.com/about_6136128_hydrogen-helium.html
4.https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/nonmetallic-elements-21/hydrogen-148/properties-of-hydrogen-571-3498/
5.http://geology.com/articles/helium/
6.http://www.sciencekids.co.nz/sciencefacts/chemistry/helium.html
Chobhi's Blog 