Greetings to everyone! Hope you guys are doing great. We have studied about the atomic theory yesterday along with basics of atoms and elements. I have also mentioned about the early or the brief 20 elements periodic table. We shall be studying the first of them, i.e., the hydrogen atom.

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Hydrogen (H) is an element with an atomic number 1. Most hydrogen atoms have one proton forming their nucleus, and there is 1 electron per hydrogen atom. Elemental hydrogen is found in a molecule of 2 H atoms with the chemical formula H₂, where 2 H atoms are bonded together by a covalent bond consisting of 2 shared electrons. Molecules containing 2 atoms are called diatomic molecules. As we will see, some of the basic elements in the brief 20 elements periodic table contain diatomic molecules in elemental form.

Representing Electrons in Atomic Symbols and Molecular Formulas

When talking about atomic behavior, there is a way to show electrons in atoms (especially the low energy of the outer shell). This was done with the writing of Lewis symbols (named after G. N. Lewis) and is also known as electron dot notation. The Lewis symbol for the hydrogen atom is

H^.

Under normal conditions elemental hydrogen occurs naturally as H₂ molecules. Hydrogen atoms could exists in thin air in the upper atmosphere and as transient species in chemical reactions. There is a simple way to represent electrons in a molecule. This is done with the Lewis formula (electron dot formula).

Properties and uses of elemental hydrogen

Pure elemental hydrogen under normal conditions is a colorless, odorless gas having the lowest density of any pure substance. Liquefied hydrogen boils at very cold -253°C and freezes at -259°C. H₂ gas is commonly used in the chemical industry whereby hydrogen reacts chemically with a large number of substances. It burns readily and releases a lot of energy. A mixture of hydrogen with oxygen or air is very explosive. Chemical reaction for the combustion of elemental hydrogen with oxygen (O₂) in the air is

2H₂ + O₂ → 2H₂O + energy

The product of this reaction is water. The hydrogen content as a fuel is a very green product because when burned or otherwise reacted to provide energy, the only product of the reaction is water, H2O. In addition, if provided with a source of electrical energy; elemental hydrogen and elemental oxygen can be produced by passing direct current through water in which the salts necessary to make the water conductive has been dissolved between two separate electrodes:

2H₂O + Electricity → 2H₂ + O₂

That is, elemental hydrogen generated by application of electrical energy made by applying electricity to water, can be transferred from one place to another. The energy generated can be transferred and used to generate electricity from fossil fuels or for other useful purposes.

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Elemental hydrogen is widely used in chemical synthesis and other industrial applications. Its preparation by electrolysis is described above. Now, it is most commonly produced by high-temperature conversion of the chief ingredient of natural gas, methane CH₄:

CH₄ + H₂O → CO + 3H₂ (at 800°C and 30 atm pressure)

Hydrogen is used in the production of many chemicals. The two most common chemicals required for hydrogen synthesis are ammonia, NH₃ and methanol (CH₃OH). The second is produced by the reaction of carbon monoxide and hydrogen:

CO + 2H₂ → CH₃OH

Methanol is produced by heating wood without air and condensing methanol from the released vapors, a process called destructive distillation. Generation of so called wood alcohol from this green biomass process can provide at least some of the methanol currently needed, thereby reducing the consumption of scarce natural gases.

Methanol has some important fuel uses. In the 1930s, before Middle East became a hub of petroleum, it was used instead of gasoline to power internal combustion engines to power a significant fraction of automobiles in French. It is now mixed with gasoline as an oxygenated product; engines using this blended mixture produce less carbon monoxide contents, leading to less pollutions. The most common use of methanol currently as a fuel is to split it into elemental hydrogen and carbon dioxide to produce hydrogen for fuel cells.

In addition to being used to make ammonia and methanol, hydrogen is added to certain parts of gasoline to increase its fuel value. Hydrogen can be added directly to coal or carbon monoxide to produce synthetic petroleum. It is also combined with unsaturated vegetable oils to make margarine and other hydrogenated oils and fats. This practice is controversial because it is suspected that these products have long-term health effects.

Hydrogen in Fuel Cells

Fuel cells are devices that enable hydrogen to “burn” at around room temperature and to produce electricity directly without going through some sort of internal combustion engine and electricity generator. A fuel cell consists of two electrically conducting electrodes, an anode and a cathode that are contacted with elemental H₂ and O₂, respectively.

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As shown in the diagram below, at the anode H₂ loses electrons (it is said to be oxidized) to produce H+ ion. At the cathode O₂ gains electrons (it is said to be reduced) and reacts with H+ ions to produce water, H₂O. The H+ ions required for the reaction at the cathode are those generated at the anode and they migrate to the cathode through a solid membrane permeable to protons (the H+ ion is a proton). The net reaction is