Energy sublevels
Within a shell, electrons are divided into sublevels by the shape of their clouds: s (spherical, 1 orbital, 2 electrons), p (dumbbell-shaped, 3 orbitals, 6 electrons), d (5 orbitals, 10 electrons), f (7 orbitals, 14 electrons). Each orbital holds at most two electrons spinning in opposite directions. Shell n has n sublevels: shell 1 has 1s; shell 2 has 2s, 2p; shell 3 has 3s, 3p, 3d; shell 4 has 4s, 4p, 4d, 4f. Electrons fill the lower-energy sublevel first, so 4s fills before 3d. In an electron formula the number of electrons is written as a superscript: boron is 1s² 2s² 2p¹. Elements are called s-, p-, d- or f-elements depending on which sublevel is filled last (14 s, 36 p, 40 d and 28 f elements, 118 in total).
“Orbital hotel”: draw rooms for each sublevel (s — 1, p — 3, d — 5, f — 7 rooms, 2 beds each). Place the electrons of N (Z = 7) and Ne (Z = 10). Drawing only.