How is the movement of the electrons different when the two hydrogen atoms are brought together

We have learned that atoms tend to react in ways that create a full valence shell, but what does this mean? Sodium (Na), for example, has one electron in its valence shell. This is an unstable state because that valence shell needs eight electrons to be full. In order to fill its valence shell, sodium has two options:

Find a way to add seven electrons to its valence shell, or

Give up that one electron so the next lower energy shell (already full) could become its new valence shell.

Which do you think is more easily accomplished?

Right, giving up one electron! Atoms like sodium, with only one or two electrons in a valence shell that needs eight electrons, are most likely to give up their valence electrons to achieve a stable state. All these atoms need is another atom that can attract their electrons!

An atom such as chlorine (Cl), that contains seven electrons in its valence shell, needs one more electron to have a full valence shell. If we use the same logic as we did for sodium, we should conclude that chlorine would rather gain one more electron than lose all seven of its valence electrons to achieve stability. Under the right conditions, atoms like chlorine will steal an electron from nearby atoms like sodium. This ability to pull electrons away from other atoms is termed electronegativity. Atoms with a valence shell that is almost full are more likely to be electronegative because they have greater reason to pull electrons towards them. Electronegative atoms are not negatively charged, but they are more likely to become negatively charged.

When an electron moves from one atom to another, both atoms become ions. An ion is any atom that has gained electrons to have a negative charge (anion) or lost electrons to have a positive charge (cation). An easy way to remember that a cation has a positive, or +, charge is to think of the letter t in the word cation as a + sign.