Hydrogen is the 1st and simplest element on the periodic table because it has only 1 proton at its center (in its nucleus). Since the proton carries a positive charge, it will attract 1 electron to it in order to balance its charge because electrons have a negative charge. Hydrogen therefore forms a neutral atom when a single electron surrounds a single proton in the nucleus, because the charges then balance each other perfectly (shown below).
The wireframes with light coloring represent a single electron. (Note: a single electron will occupy much less volume when it is isolated and not surrounding a nucleus. See Understanding Electrons) Hydrogen only has 1 electron shell (a spherical s-orbital) containing a single electron. We describe it with an electron configuration of 1s1. (This “1–s–1” means shell 1, s-orbital, containing 1 electron.)
This image provides another view of the spherical hydrogen atom:
The size of the nucleus in the center of these images is exaggerated. If the electron cloud were the size of a large football stadium, the nucleus would be the size of a dime at the center of the field.
The electron surrounds the nucleus by forming a sphere-shaped cloud of electron density around it — the s-orbital. The fact that hydrogen has only one electron cancelling charge and field with the nuclear proton makes hydrogen particularly keen to keep its electron. This gives it a high ionization energy (1,312 kJ/mol = 13.6 eV), making it difficult for other atoms to steal its electron.
Hydrogen is also quite reactive in search of another electron to pair with its single electron. When two electrons pair, they form a di-electron state, which is a much more stable and desired state than an unpaired electron. (See Understanding Electrons)
Electron pairing and symmetry will often happen even at the expense of the atom having a neutral charge. Some atoms easily form ions by gaining or losing electrons in order to achieve full, symmetrical electron shells. This stabilizes them more than having the same numbers of protons and electrons.
In the presence of more electronegative non-metal atoms (like chlorine), hydrogen can lose its electron and the (acidic) hydrogen ion (H+) can form (below, left). The stronger an acid, the more H+ ions it produces in solution. An H+ ion is an exposed proton, which is why strong acids can be so corrosive. Each H+ ion is desperately seeking an electron in which to clothe its bare proton nucleus. It does so by taking an electron from another substance around it, which results in a (sometimes violent) chemical reaction.
In the presence of metal atoms (like sodium), hydrogen can attract an electron and the (alkaline) hydride (H–) ion can form (below, right). This is because metal atoms have low ionization energies and some are rich in delocalized electrons.
Dihydrogen Molecule (H2)
When two hydrogen atoms bond to form an H2 molecule (shown below), the two bonding electrons form a single di-electron state. This is a different state than two single electrons. It is a boson state where the two electron wave functions are completely superimposed upon one another for maximum magnetic field cancellation. This binds the two nuclei together in a covalent bond, although the nuclei remain at a distance because protons repel each other.
We see this same di-electron formation in the individual helium (He) atom.
Hydrogen is important for many reasons. Some of these include:
It is the most abundant element in the universe because the hydrogen atom is the simplest atom — 1 proton + 1 electron.
Hydrogen makes up stars, which fuse the hydrogen atoms together to form helium atoms, resulting in a large release of heat energy — fusion energy. As stars go through their stellar life cycles, they forge the heavier elements from the smaller elements. Stars are literally the matter-making machines of the universe, and hydrogen is the raw material.
Hydrogen (H2) combines with oxygen (O2) to form water (H2O), the most essential compound for sustaining life on Earth. When hydrogen and oxygen combine, a large amount of energy is released as heat because the product, H2O, is so much more stable than the elemental gases individually. This is called a combustion reaction because burning is occurring.
Burning is the chemical process of combining with oxygen. It is the heat from this combustion reaction that is used to power the rocket engines of the space shuttle, for example, when liquid oxygen and liquid hydrogen are used as the fuel. This is a very clean-burning fuel since water vapor is the “waste” product.
2H2 + O2 —> 2H2O + explosive heat
The formation of water from hydrogen and oxygen is a reaction that can also be reversed. Hydrogen and oxygen can be obtained by splitting water molecules apart. The most common way to do this is by electrolysis — using electricity to split the water.
Electricity + 2H2O —> 2H2 + O2
The reverse is also true. Electricity can be obtained by allowing hydrogen and oxygen to react in a non-explosive way. This is what occurs in a hydrogen-oxygen battery, known as a hydrogen fuel cell.
2H2 + O2 —> Electricity + 2H2O
On space vehicles and space stations, these two processes are both used, and one can be used to supplement the other. Water can be turned into oxygen for breathing if needed, but it also consumes electricity. Oxygen can be turned into water if needed, which also produces electricity. Or oxygen can be turned into electricity if needed, which also produces water. And hydrogen is an essential part of these processes.
(Images: Wikimedia commons)
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