Lesson 4Intermediate~7 min
Electrons and Shells
How electrons fill simplified energy levels, and why the outermost shell decides an element's chemistry.
electronsshellsvalence
Step 1 of 7
Concept
The negative particle
Electrons carry a negative charge and are extraordinarily light — about 1/1836 the mass of a proton. Nearly all of an atom's volume is the region its electrons occupy.
In a neutral atom, electron count equals proton count, so sodium (11 protons) has 11 electrons.