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. 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 Electrons & the Hierarchy of Forces)
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.
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