Hydrogen with symbol H is the first element in the periodic table. It has the simplest atomic structure with one proton and one electron. It has the least atomic mass. It is the most abundant element in the universe. Its unique properties make it useful for many applications including electricity production, and compound structure determination. Further, being the simplest element it is treated as the model element for developing mathematical models and later extended to other elements with appropriate assumptions and modifications. In this blog, I discuss the properties that make hydrogen suitable for its applications. I also discuss how the modeling studies with hydrogen have been instrumental to understanding atoms, hydrogen and every other element and in the development of quantum chemistry as a separate field of study. I try not to delve much into scientific aspects and thereby make this blog comprehensible for all readers regardless of their background in Science.
Genesis of Hydrogen
Hydrogen is the most abundant element in the universe. The universe consists of 92% Hydrogen, 7% Helium and 1% of all the other elements. It is the first element believed to have been formed when this universe was created. In my previous blog, Helium – the coolest element and the second most abundant element in the universe – Foxtail Research, I had discussed the formation of Helium which was the second element formed after hydrogen.
The big bang theory, the steady state theory and other theories which postulate about the creation of the universe state that the universe initially consisted of dense matter made up of neutrons (represented as 0n1). These neutrons at very high temperatures of the order of millions of ℃ exploded forming protons (represented as 1p1), electrons (represented as -1e0) and high energy particles called neutrinos.
0n1 -> 1p1 + -1e0 + 𝒗
The protons then fused to form hydrogen. High energies were released during these reactions in the core of the sun and with such huge energies other elements and other parts of the universe were formed.
Production of Hydrogen
Though Hydrogen element is abundant in the universe, it is rare on the earth. This is because it is lighter than air and it can escape easily from the earth’s atmosphere. The point to be noted is that even though the hydrogen element or hydrogen molecule is rare on earth, hydrogen is present in abundance in many compounds. It is present in water, natural gas, hydrocarbons, living matter (carbohydrates, proteins, nucleic acids) and in many more compounds. Hydrogen is extracted from the compounds mainly from natural gas and the extracted hydrogen finds use as fuel, for production of compounds such as ammonia, for petroleum refining and others.
Methane or Natural gas is used as the major source for producing hydrogen. This is an environmentally expensive process as it releases greenhouse gases. Hydrogen is extracted in gaseous state and is stored and transported in cylinders. Even though Natural gas is the major source, water is a better available option for extraction of hydrogen due to its abundance. 75% of earth’s crust is covered by water. Electrolysis of water produces hydrogen but again it is an expensive process as it requires huge amounts of electric current. Still, extracting hydrogen from water is a favorable situation as water is a renewable resource and there is minimal environmental impact. Research is underway to capture solar energy from sunlight to electrolyse water and to generate hydrogen. The DOE website Hydrogen Production Processes | Department of Energy gives the various approaches and research undertaken for producing hydrogen.
We have seen hydrogen is in abundance in the universe and this has made the universe to exist in a state with abundant energy. Further, Nature has been able to use the enormous amounts of energy available in hydrogen to create other elements. Similarly, in the earth, Nature has been able to extract hydrogen and use it for creating energy in the form of food for sustaining life in the earth. The classic process is photosynthesis which seamlessly occurs at normal temperatures. Plants use sunlight, water and carbon-di-oxide (exhaled by living forms) to extract hydrogen from water (also releasing oxygen for living forms to inhale) and the hydrogen thus generated is used for synthesizing carbohydrates to provide food for living forms. Some forms of microorganism too are able to extract hydrogen from water at normal temperatures by using catalysts. It will be a break-through research if we can replicate this process to generate and use hydrogen as those microorganisms or Nature.
Some of the properties of hydrogen and its uses/applications
Hydrogen in fuel cells
A fuel cell is one in which fuel is supplied continuously to the cell and the energy released is used to produce electric current. In a hydrogen fuel cell, hydrogen is produced from sources such as methane or water and is supplied into the cell. Inside the cell, electrons and protons are generated from the supplied hydrogen at the appropriately charged electrodes.
- The electrons generated are routed through an external circuit to produce electric current.
- The protons are passed through a solution (called an electrolyte) to react with oxygen and to release water as the by-product.
Thus, the only by-product is water which is environmentally safe.
The two factors, routing of electrons into an electric circuit and release of water as the only by-product, makes fuel cells an economical and eco-friendly technology for electricity generation. However, the disadvantage here is that the hydrogen used as a fuel is generated from sources such as methane which is economically and environmentally expensive. This is where a break-through research for generating hydrogen from water in an economically and environmentally friendly process will pave the way for a sustainable process for energy generation.
Compound structure determination
Synthesis or extraction of a compound either from a chemical or biochemical process has to be verified and qualified to ensure that the desired compound is generated from the process. Spectroscopy is one of the methods used to determine the compound that is produced or synthesized. If it is a well-known process, then the structure of the compound will be known and the peaks or signals generated by spectrochemical methods will be used for verification. On the other hand, in a research or discovery process, the structure of the compound may not be known yet. One may not know the end product from the reaction. Spectroscopy comes in handy in such scenarios and the spectral output is interpreted to determine the structure of the compound.
Hydrogen NMR (Nuclear Magnetic Resonance) Spectroscopy is one such powerful spectroscopy technique regularly employed in laboratories to determine the structure of compounds which have hydrogen in it. The magnetic and spinning property of hydrogen nuclei comes handy in this technique. The nuclei of hydrogen have a spin. It spins around its axis and since the proton in the nucleus is electrically charged, it generates a magnetic moment making it behave like a tiny magnet. When an electromagnetic radiation of constant frequency (in radio frequency region) is irradiated in the compound by varying magnetic field strengths, a particular external magnetic field strength resonates with the magnetic field strength of hydrogen nuclei (called as magnetic resonance), and a peak/signal gets generated. The structure of the compound is determined by interpreting the peaks/signals. Some of the characteristics of the spectrum that help in interpretation include:
- The number of peaks or signals depends on the number of types of hydrogen nuclei present in the compound
- The relative height of each peak tells the number of hydrogen atoms present in each type
- Each signal gets split based on the number of neighboring hydrogen nuclei present in the compound
The magnetic field strength of each nucleus depends on the electron environment around it.
- If hydrogen is bonded or is in the vicinity of another element which can draw more electrons towards it, then the hydrogen nuclei are less shielded by electrons making its magnetic field strength lesser and thereby exhibiting resonance at lesser external magnetic field strengths and exhibiting signals at lesser frequency.
- If hydrogen is bonded or is in the vicinity of another element which has tendency to donate electrons, then the hydrogen nuclei are more shielded by electrons making its magnetic field strength higher and thereby exhibiting resonance at higher external magnetic field strengths and exhibiting signals at higher frequency.
Theoretical studies, quantum chemistry and model development
Hydrogen has the simplest atomic structure with one proton in the nucleus and one electron. As it has the simplest atomic structure, mathematical and theoretical models to understand atomic structure and properties of elements were first developed with hydrogen. This model was used as the baseline model and later extended to elements having more than one electron by applying appropriate modifications and assumptions.
Neils Bohr proposed an atomic model for hydrogen in which he proposed the sole electron to be moving in a circular orbit around the nuclei. His model was restricted to hydrogen and could not be extended to other elements. Later, Schrodinger developed a mathematical model called the wave mechanical model. In this model, the electron is treated as a wave (meaning it is moving around) and he proposed a probabilistic model. According to the model:
- The electron can exist at different locations in space in the atom
- The electron will exhibit different energies at different locations
- The energies exhibited by the electrons are discrete, i.e. they possess only certain energy values, i.e. energies are quantized
Schrodinger calculated the probabilities for the electron to exist in those locations in space (those locations or regions are called orbitals), their energies and proposed shapes and orientation of those orbitals. This model from hydrogen was further extended to elements with more than one electron by accounting for electron-electron repulsion and then treating each electron in isolation as a one-electron model as hydrogen.
Hydrogen for storage and transportation
Being the lightest element, hydrogen carries an astonishing amount of energy per unit. On a mass basis, hydrogen has nearly three times the energy content of gasoline. That said, it should be noted that the situation flips on a volume basis. Liquid hydrogen has one-third the energy density as gasoline. Hence, solutions where hydrogen can be compressed and stored and then liquefied as needed for applications will be an efficient and useful method for utilizing the properties of hydrogen for practical applications. This will require innovations in hydrogen storage, and liquefaction. Major challenges here are: (1) Hydrogen gas is inflammable, i.e. it burns (2) Hydrogen has a very low melting point at -259℃. So liquefying hydrogen gas to such low temperatures, will pose problems for storage.
Summary
In this blog, I discussed on a high level the production and properties of hydrogen and how some its properties help in its applications. Hydrogen is a promising element for environmental-friendly energy generation, and transportation though it poses certain challenges. Research is underway in areas such as fuel cell technology, solar energy powered hydrogen production and microbial technologies. The unique properties of hydrogen such as its spinning nuclei have enabled the interpretation of compound structure under Nuclear Magnetic Resonance Spectroscopy. Being the smallest and simplest element, it has been used as the model element for atomic model development by theoretical scientists and in development of Quantum chemistry as a separate field of study.
Bibliography
(1) US Department of Energy website: Home | Hydrogen Program – https://www.hydrogen.energy.gov/
(2) Concise Inorganic Chemistry, J.D.Lee, Fifth Edition, Educational Low-Priced Books Scheme (ELBS) funded by the British Government
(3) Chemistry, Steven S. Zumdahl, Second Edition, D. C. Heath and Company
(4) Organic chemistry, T. W. Graham Solomons, John Wiley & Sons, Inc.
Image courtesy: geralt – Pixabay
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