Eli5: How are electrons distributed in an atom’s shell and how do they interact with other atoms to form ionic and covalent bonds?

Question

I heard having 8 electrons is important, can you explain? Thanks.

In: Chemistry

Answer 1

The waves of a vibrating string are a familiar sight. It’s less intuitive to picture the kinds of [“waves”](https://en.wikipedia.org/wiki/Spherical_harmonics) that occupy 3-D space around a center point. In the atom, the behavior of electrons must be represented with waves.

The topmost 4 orbitals in the topmost linked diagram correspond to the s and p orbitals in chemistry books.

The early-20th-century math of Paul Dirac explains why only 2 electrons are allowed in each orbital. So that’s 4 x 2 = 8 total electrons in filled s and p orbitals.

Next, it’s all about energy:

A system with things *above* the minimum allowed energy will tend to change, in the way that results in a stable system of *lower* energy.

If you calculate the minimum energy for electrons arranged around certain nuclei, it turns out that stealing or losing an electron as needed, to bring the total to 7 + 1 = 8, or 9 – 1 = 8, will be a more stable arrangement, at a lower total energy.

That’d mean you now have charged ions. Opposite electric charges will always attract. That’s the basis of an ‘ionic bond.’

Other nuclei don’t achieve lowest-energy systems by stealing or losing electrons, but rather by sharing electrons. That sharing is the basis of a ‘covalent bond.’