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Gaffer Variety:
Elements 5 SN2 007:
By Willie Gaffer:
No we can look at the individual elements and their properties. We will take them in order of atomic Number.
Hydrogen is the first element in the periodic table of the elements and is represented by the symbol H. The atomic number is 1 and the atomic weight is 1.00797. Hydrogen has a melting point of -259.14°C and a boiling point of -252.8°C. It has a density at 0°C 0.08987 gram per liter and a valence of 1. It is the most common element in the universe and it can exist as a gas in pairs of atoms (H2) at room temperature. It is odorless, tasteless, colorless, and highly flammable. When hydrogen gas burns in oxygen, the output is only water and a great deal of heat energy. That is the main reason the fuel cell using hydrogen as fuel is seen as a potential candidate for replacing the gasoline engine.
Hydrogen has the smallest atoms of any element containing just one proton, and one electron. The valence of 1 makes it eager to combine with other atoms. According to the big bang theory, hydrogen atoms were among the first atoms to form in the early universe. The hydrogen nuclei, protons, formed within three minutes after the big bang. The protons began to combine with electrons to form hydrogen atoms when the universe was about 300,000 years old. This process of combination continued until the universe was about one million years old. In stars, hydrogen nuclei combine with each other in nuclear reactions to build helium atoms. These high-energy reactions create the light and heat of the Sun and most other stars.
It is not an exaggeration to say that hydrogen is the most important element in the universe. Nine out of every ten atoms in the universe are hydrogen. When we notice that helium accounts for another 9 percent we don’t have much left for all the rest of the elements, about 1 percent. Hydrogen can combine chemically with almost every other element and forms more compounds than any other element. These compounds include water, many minerals, and hydrocarbons. Common hydrocarbons are petroleum and natural gas from which most of our modern energy is made. Hydrogen is usually found in compounds. Pure hydrogen gas rarely occurs in nature.
The other isotopes of hydrogen are deuterium (with one neutron), and tritium (with two neutrons). Hydrogen gas does not usually react with other chemicals at room temperature. That is, it does not split into two hydrogen atoms to combine with other chemicals. The bond between the hydrogen atoms is very strong and can only be broken with a large amount of energy. However, when heated with a flame or a spark, hydrogen gas will react violently with oxygen in the air to produce water in the following reaction:
2H2 + O2 → 2H2O
This chemical equation shows that two hydrogen molecules and one oxygen molecule combine to form two molecules of water. This reaction releases energy, lots of it.
This is just a surface look at the element hydrogen. There is much more that can come later in other investigations. For now, let us move on to helium.
Helium (He) is an inert, colorless, odorless gaseous element. In our periodic table we find it at the top of group VIII a. It is one of the noble gases with the atomic number of 2. With only one shell and two electrons, helium is monatomic as it is and can occur as a very stable molecule. The valence is 0. The only element lighter than helium is hydrogen, but helium is chemically inert. This makes it very preferable for use in balloons. It was hydrogen that caused the Hindenburg disaster and precipitated the switch to helium.
Helium is the most difficult of all gases to liquefy and is impossible to solidify in ordinary conditions. That behavior makes liquid helium extremely useful as a refrigerant and for experimental work in producing and measuring temperatures close to absolute zero. Liquid helium can be cooled almost to absolute zero at normal pressure by rapid removal of the vapor above the liquid. At a temperature slightly above absolute zero, it is transformed into helium II, or superfluid helium. At that temperature it acquires unique physical properties. It has no freezing point, and its viscosity is apparently zero.
Helium is the second most abundant element in the universe, after hydrogen, but it is rare on earth. We usually find it mixed with natural gas trapped in underground pockets. Once helium is released it is so light it escapes the earth's atmosphere and cannot be recovered.
Because it is noncombustible, helium is preferred to hydrogen as the lifting gas in lighter-than-air balloons. It has slightly less lifting power than hydrogen. Helium is used to pressurize and stiffen the structure of rockets before takeoff and to pressurize the tanks of liquid hydrogen or other fuel in order to force fuel into the rocket engines. It is useful for this application because it remains a gas even at the low temperature of liquid hydrogen. A potential use of helium is as a heat-transfer medium in nuclear reactors because it remains chemically inert and non-radioactive under the conditions that exist within the reactors.
Helium is 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. Helium is used in place of nitrogen as part of the synthetic atmosphere breathed by deep-sea divers, caisson workers, and others, because it reduces susceptibility to the bends. This synthetic atmosphere is also used in medicine to relieve sufferers of respiratory difficulties because helium moves more easily than nitrogen through constricted respiratory passages. In surgery, beams of ionized helium from synchrocyclotron sources are proving useful in treating eye tumors, by stabilizing or even shrinking the tumors. Such beams are also used to shrink blood-vessel malformations in the brains of patients.
Next time we will take a look at Lithium and go on with the other elements.