Hydrogen gas is supplied to the anode of the fuel cell. The anode is coated with platinum, which acts as a catalyst to break down the hydrogen into protons and electrons. If a circuit is connected between the anode and cathode then the electrons can travel through the circuit and provide power to any load that is connected as part of the circuit. Hydrogen combines with other elements, forming a number of compounds, including common ones such as water (H 2 O), ammonia (NH 3), methane (CH 4), table sugar (C 12 H 22 O 11), hydrogen peroxide. The hydrogen is attached directly to a highly electronegative atoms, causing the hydrogen to acquire a highly positive charge. Each of the highly electronegative atoms attains a high negative charge and has at least one 'active' lone pair. HYDROGEN IS THE universe's simplest atom: a single electron orbiting a single proton. In a fuel cell, incoming hydrogen gas is separated by a catalyst at the anode into protons and electrons. How hydrogen atoms share valence electrons to form covalent bond and hydrogen molecule (H 2). First, if we write the electron configuration of hydrogen, you will realize that hydrogen has only one valence electron in the one-s orbital (1s 1).
How hydrogen atoms share valence electrons to form covalent bond and hydrogen molecule (H2)
First, if we write the electron configuration of hydrogen, you will realize that hydrogen has only one valence electron in the one-s orbital (1s1). As a result, the hydrogen atom is unstable. Because it’s unstable, hydrogen will always bond with another atom so that it can become stable and achieve a stable electron configuration similar to that of helium (He): 1s2.
Where can hydrogen get this other electron?
One way hydrogen can get this other electron is to bond with another hydrogen atom. So, let’s imagine that we have two hydrogen atoms with their valence electrons depicted by these two circles.
As you can tell, the orange circle with the plus sign describes the nucleus, which usually carries a positive charge because of the protons in it. While the red circle with the minus sign describes the electron, which usually carries a negative charge.
To keep the hydrogen atom intact, its nucleus must attract its electron (opposite attract). Now, when the two separate hydrogen atoms are far apart, there is virtually no interaction between the two atoms. However, as the two hydrogen atoms gain energy and move toward each other, they reach a certain distance where the two hydrogen atoms feel the presence of each other.
That is the nucleus of the hydrogen atom on the left will attract the electron of the hydrogen atom on the right. Likewise, the nucleus of the hydrogen atom on the right will attract the electron of the hydrogen atom on the left. As the attractive force between the two atoms strengthens, the atoms pick up more speed and continue to move closer to each other. However, if these atoms suddenly become too close, they will immediately repel each other.
Why will the hydrogen atoms repel each other?
If they are too close, the nucleus of the left atom will repel the nucleus of the right atom. Likewise, the electron of the left atom will repel the electron of the right atom (like charges repel).
When’s the covalent bond formed between the two hydrogen atoms?
When the attractive and repulsive forces between the two hydrogen atoms is just right, they will form the covalent bond. Here is a model to help you visualize its creation.
Notice, because the electrons are equally attracted to the nuclei of both atoms, they are located between the two atoms. And these electrons hover and spend most of their time in the region once the covalent bond is created. The more covalent bonds atoms make, the stronger the force of attraction between them.
It’s tiring to keep drawing circles and pluses and minuses to explain covalent bonding. As a result, chemists have a shorthand for doing this. If we draw a line to connect the two dots depicting the two electrons shared by the hydrogen atoms, we will get something like a dash (__). The dash is a symbol chemist use to denote a covalent bond formed between two atoms.
If we have three of these dashes between atoms, it follows that we have three pair of electrons (6 electrons) shared between them. So, we can depict the hydrogen molecule as a structural formula like this: H__H (read as single bond between hydrogen atoms). But it’s not always necessary to show the dash anytime we write the chemical formula for a molecule. As a result, chemists sometimes condense the H__H to H2.
If you want to learn more about chemical bonding, click here.
Article - Physical and chemical properties
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William Lee JollyEmeritus Professor of Chemistry, University of California, Berkeley. Author of The Synthesis and Characterization of Inorganic Compounds and others.
Alternative Title: H
Hydrogen (H), a colourless, odourless, tasteless, flammable gaseous substance that is the simplest member of the family of chemical elements. The hydrogen atom has a nucleus consisting of a proton bearing one unit of positive electrical charge; an electron, bearing one unit of negative electrical charge, is also associated with this nucleus. Under ordinary conditions, hydrogen gas is a loose aggregation of hydrogen molecules, each consisting of a pair of atoms, a diatomic molecule, H2. The earliest known important chemical property of hydrogen is that it burns with oxygen to form water, H2O; indeed, the name hydrogen is derived from Greek words meaning “maker of water.”
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Although hydrogen is the most abundant element in the universe (three times as abundant as helium, the next most widely occurring element), it makes up only about 0.14 percent of Earth’s crust by weight. It occurs, however, in vast quantities as part of the water in oceans, ice packs, rivers, lakes, and the atmosphere. As part of innumerable carboncompounds, hydrogen is present in all animal and vegetable tissue and in petroleum. Even though it is often said that there are more known compounds of carbon than of any other element, the fact is that, since hydrogen is contained in almost all carbon compounds and also forms a multitude of compounds with all other elements (except some of the noble gases), it is possible that hydrogen compounds are more numerous.
Elementary hydrogen finds its principal industrial application in the manufacture of ammonia (a compound of hydrogen and nitrogen, NH3) and in the hydrogenation of carbon monoxide and organic compounds.
Hydrogen has three known isotopes. The mass numbers of hydrogen’s isotopes are 1, 2, and 3, the most abundant being the mass 1 isotope generally called hydrogen (symbol H, or 1H) but also known as protium. The mass 2 isotope, which has a nucleus of one proton and one neutron and has been named deuterium, or heavy hydrogen (symbol D, or 2H), constitutes 0.0156 percent of the ordinary mixture of hydrogen. Tritium (symbol T, or 3H), with one proton and two neutrons in each nucleus, is the mass 3 isotope and constitutes about 10−15 to 10−16 percent of hydrogen. The practice of giving distinct names to the hydrogen isotopes is justified by the fact that there are significant differences in their properties.
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Paracelsus, physician and alchemist, in the 16th century unknowingly experimented with hydrogen when he found that a flammable gas was evolved when a metal was dissolved in acid. The gas, however, was confused with other flammable gases, such as hydrocarbons and carbon monoxide. In 1766 Henry Cavendish, English chemist and physicist, showed that hydrogen, then called flammable air, phlogiston, or the flammable principle, was distinct from other combustible gases because of its density and the amount of it that evolved from a given amount of acid and metal. In 1781 Cavendish confirmed previous observations that water was formed when hydrogen was burned, and Antoine-Laurent Lavoisier, the father of modern chemistry, coined the French word hydrogène from which the English form is derived. In 1929 Karl Friedrich Bonhoeffer, a German physical chemist, and Paul Harteck, an Austrian chemist, on the basis of earlier theoretical work, showed that ordinary hydrogen is a mixture of two kinds of molecules, ortho-hydrogen and para-hydrogen. Because of the simple structure of hydrogen, its properties can be theoretically calculated relatively easily. Hence hydrogen is often used as a theoretical model for more complex atoms, and the results are applied qualitatively to other atoms.
Physical and chemical properties
The Table lists the important properties of molecular hydrogen, H2. The extremely low melting and boiling points result from weak forces of attraction between the molecules. The existence of these weak intermolecular forces is also revealed by the fact that, when hydrogen gas expands from high to low pressure at room temperature, its temperature rises, whereas the temperature of most other gases falls. According to thermodynamic principles, this implies that repulsive forces exceed attractive forces between hydrogen molecules at room temperature—otherwise, the expansion would cool the hydrogen. In fact, at −68.6° C attractive forces predominate, and hydrogen, therefore, cools upon being allowed to expand below that temperature. The cooling effect becomes so pronounced at temperatures below that of liquid nitrogen (−196° C) that the effect is utilized to achieve the liquefaction temperature of hydrogen gas itself.
normal hydrogen | deuterium | |
---|---|---|
Atomic hydrogen | ||
atomic number | 1 | 1 |
atomic weight | 1.0080 | 2.0141 |
ionization potential | 13.595 electron volts | 13.600 electron volts |
electron affinity | 0.7542 electron volts | 0.754 electron volts |
nuclear spin | 1/2 | 1 |
nuclear magnetic moment (nuclear magnetons) | 2.7927 | 0.8574 |
nuclear quadrupole moment | 0 | 2.77(10−27) square centimetres |
electronegativity (Pauling) | 2.1 | ~2.1 |
Molecular hydrogen | ||
bond distance | 0.7416 angstrom | 0.7416 angstrom |
dissociation energy (25 degrees C) | 104.19 kilocalories per mole | 105.97 kilocalories per mole |
ionization potential | 15.427 electron volts | 15.457 electron volts |
density of solid | 0.08671 gram per cubic centimetre | 0.1967 gram per cubic centimetre |
melting point | −259.20 degrees Celsius | −254.43 degrees Celsius |
heat of fusion | 28 calories per mole | 47 calories per mole |
density of liquid | 0.07099 (−252.78 degrees) | 0.1630 (−249.75 degrees) |
boiling point | −252.77 degrees Celsius | −249.49 degrees Celsius |
heat of vaporization | 216 calories per mole | 293 calories per mole |
critical temperature | −240.0 degrees Celsius | −243.8 degrees Celsius |
critical pressure | 13.0 atmospheres | 16.4 atmospheres |
critical density | 0.0310 gram per cubic centimetre | 0.0668 gram per cubic centimetre |
heat of combustion to water (g) | −57.796 kilocalories per mole | −59.564 kilocalories per mole |
Hydrogen is transparent to visible light, to infrared light, and to ultraviolet light to wavelengths below 1800 Å. Because its molecular weight is lower than that of any other gas, its molecules have a velocity higher than those of any other gas at a given temperature and it diffuses faster than any other gas. Consequently, kinetic energy is distributed faster through hydrogen than through any other gas; it has, for example, the greatest heat conductivity.
A molecule of hydrogen is the simplest possible molecule. It consists of two protons and two electrons held together by electrostatic forces. Like atomic hydrogen, the assemblage can exist in a number of energy levels.
Ortho-hydrogen and para-hydrogen
Hydrogen Electrons Number
Two types of molecular hydrogen (ortho and para) are known. These differ in the magnetic interactions of the protons due to the spinning motions of the protons. In ortho-hydrogen, the spins of both protons are aligned in the same direction—that is, they are parallel. In para-hydrogen, the spins are aligned in opposite directions and are therefore antiparallel. The relationship of spin alignments determines the magnetic properties of the atoms. Normally, transformations of one type into the other (i.e., conversions between ortho and para molecules) do not occur and ortho-hydrogen and para-hydrogen can be regarded as two distinct modifications of hydrogen. The two forms may, however, interconvert under certain conditions. Equilibrium between the two forms can be established in several ways. One of these is by the introduction of catalysts (such as activated charcoal or various paramagnetic substances); another method is to apply an electrical discharge to the gas or to heat it to a high temperature.
The concentration of para-hydrogen in a mixture that has achieved equilibrium between the two forms depends on the temperature as shown by the following figures:
![Hydrogen Hydrogen](/uploads/1/3/4/6/134692142/605529792.png)
Essentially pure para-hydrogen can be produced by bringing the mixture into contact with charcoal at the temperature of liquid hydrogen; this converts all the ortho-hydrogen into para-hydrogen. The ortho-hydrogen, on the other hand, cannot be prepared directly from the mixture because the concentration of para-hydrogen is never less than 25 percent.
The two forms of hydrogen have slightly different physical properties. The melting point of para-hydrogen is 0.10° lower than that of a 3:1 mixture of ortho-hydrogen and para-hydrogen. At −252.77° C the pressure exerted by the vapour over liquid para-hydrogen is 1.035 atmospheres (one atmosphere is the pressure of the atmosphere at sea level under standard conditions, equal to about 14.69 pounds per square inch), compared with 1.000 atmosphere for the vapour pressure of the 3:1 ortho–para mixture. As a result of the different vapour pressures of para-hydrogen and ortho-hydrogen, these forms of hydrogen can be separated by low-temperature gas chromatography, an analytical process that separates different atomic and molecular species on the basis of their differing volatilities.
Quick Facts
Hydrogen Electrons
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