Valence electrons, (noun, “VAY-lance Eel-ek-trons”)
Valence electrons are the electrons in an atom farthest from the nucleus. An element’s number of valence electrons helps predict how atoms of that element interact with other atoms.
Atoms consist of three types of particles: protons, neutrons and electrons. Protons and neutrons pack together into a tiny center — the nucleus. Electrons whiz around the surrounding space. That surrounding space is organized into levels.
Electrons fill these levels from the inside out. The level closest to the nucleus fills first, with two electrons. If the atom has more than two, these overflow electrons must go to the next level. Then the next and next, and so on, as each level fills up. Valence electrons are those that live in whichever level is outermost.
To be stable, atoms need a complete set of valence electrons to fill their outermost levels. For most elements, that number is eight. Atoms with fewer than eight valence electrons are more likely to take, donate or share another atom’s valence electrons.
Consider this example. A neutral chlorine atom has seven valence electrons. A neutral sodium atom has only one valence electron. Neither has a complete set of eight. Losing one electron is “easier” than stealing seven. So that’s what sodium does — it donates one electron to chlorine. In doing so, the two atoms form a chemical bond — becoming sodium chloride, which you know as table salt.
In a sentence
The valence electrons of rare earth elements grant them special abilities that make modern technology possible.