4 Types of elements

The elements of the modern table are classified into four types:

1. Noble (inert) gases: last vertical column of the p-block (group zero/18). Configuration ends with np⁶ (helium 1s²). All sublevels of the period are filled, so they are completely stable and form compounds with extreme difficulty.
2. Representative elements: the s-block and the p-block except the zero group. All energy levels are full except the outermost, and they tend to attain the configuration ns² np⁶ by losing, gaining or sharing electrons.
3. Main (d-block) transition elements: the d sublevel is filled successively.
4. Inner transition elements: the f-block, where f is filled successively.

The sixth period contains all four types (noble gas Rn is in the 6th period; Cs and Ba, representative; Hf to Hg, d-block; and the lanthanides), so it has four types.