Bonds: Hydrogen

The simplest atom is hydrogen consisting of a nucleus with a single proton and a single electron. The most common atom, that is element  in the known universe is hydrogen. Stars, such as the Sun are formed when huge clouds of hydrogen gas in space collapse under the influence of gravity. When the center of such a collapsing cloud becomes dense enough and hot enough nuclear fusion, the same process which powers the hydrogen bomb, occurs forming a star.

Unlike helium discussed in an earlier post hydrogen does not like to live in isolation. The single electron in a hydrogen atom occupies an unfilled electron shell. If importance is that hydrogen is the only atom to which quantum mechanics equations can be applied and solved exactly. This is fortunate because the functions that result from those equations, hydrogenic orbitals are used to calculate approximate solutions to quantum mechanics equations applied to more complex atoms and molecules.

Hydrogen's unfilled shell wants a second electron. However if a second electron is just added the atom has an overall negative(-1) charge which is not especially stable. Ideally and atom wants to fill its electron shells without giving the stuff made up of that matter an overall positive or negative charge. A way for hydrogen to accomplish this is to partner with another hydrogen and share a pair of electrons.

When this happens the two electrons spend more time on average between the nuclei. Because there is more negative charge on average between the nuclei than elsewhere the positive charged nuclei are pulled together by this "cloud" of negative charge. This is how bonds are formed.  Two atoms that form a bond form a molecule.

Atoms: Helium

Chemists rarely work with isolated atoms because most atoms want to combine with other atoms via the "glue", bonds that hold them together. One atom that does love existing in isolation is helium. Helium is used in applications as trivial as party balloons, in critical industrial welding and in crucial medical equipment such as the MRI.

The name helium derives from the name of the Greek Sun god  Helios. Helium was discovered in the Sun before it was discovered on earth by studying the visible spectrum of sunlight.

The most common helium nucleus contains two protons and two neutrons. When electronically neutralized by a swarm of two electrons Helium assumes its most energetically stable state. That is also its lowest energy state.  In order for an atom to combine with, to react with another atom it must be willing to give up, share or take on an electron. This is simply not the case for helium.

Helium's two electrons  occupy an imaginary spherical layer of charge called an electron shell. For helium this "shell" can contain two electrons. If one could force the lowest energy form of  helium to take on an electron it would occupy the next bigger in radius or higher energy shell becoming a negative charged atom known as an anion.

Helium can be converted to a positive charged cation by removing an electron. One way to do that is to subject helium to a very strong positive electric field which pulls the electron away. This is not a happy situation for a helium atom which will snatch the electron from the first atom it encounters to return to zero charge.

Helium is the lowest atomic number atom among nobel gases which include neon, argon, krypton, xenon and radon. The nobility of these atoms derives from their preference for not reacting with other atoms. The uncharged form of these atoms have closed outer electron shells. All the electron shells inside of the outer electron shell are also filled. This is the most stable form the atom can achieve. Atoms are most energy stable when all their electron shells are filled to capacity.

Helium gas is a declining limited resource that is a byproduct of  natural gas production. Terrestrial helium is produced from radioactive decay which produces alpha particles which are identical to helium nuclei. When these nuclei grab a couple of electrons helium atoms result.

With two protons and two neutrons helium is not the simplest atom. That's hydrogen. You might wonder why not start with the simplest atom. My goal here was to start with an atom that exists in isolation.