Element

Element was a term applied to different substances.

Chemical elements
There were 118 known chemical elements organised into the periodic table, (PROSE: Iris Wildthyme y Señor Cientocinco contra Los Monstruos del Fiesta, The Big Crunch et al) one of which was hydrogen. (TV: Castrovalva) Atomic number and atomic weight were important aspects of elements. (TV: The Krotons)

According to the Eleventh Doctor, elements were forged in the heart of stars million of years in the past. The explosion of these stars scattered the elements into space and formed new stars and planets. They continued to come together and burst apart to form "shoes and ships and sealing wax, and cabbages and kings" and eventually formed lifeforms like Merry Gejelh. (TV: The Rings of Akhaten)

Greek elements
Aristotle of the ancient Greeks believed everything was created from four elements: Earth, Air, Water, and Fire. (PROSE: The Burning)

Alchemists believed that quintessence was the spirit which infused and informed these four elements. (PROSE: The Book of the War)

One belief about the Eyes of the Schirron was that they were physical embodiments of the four elements of Earth, Air, Fire, and Water. (PROSE: Sky Pirates!)

According to Jack Harkness, Fairies controlled the elements of Fire, Water, and Air. (TV: Small Worlds)

The Eighth Doctor noted that by the 1890s, humans had prefered this romantic idea over Democritus' more accurate understanding of the natural world for two thousand years. (PROSE: The Burning)

Chinese elements
The Tenth Doctor and Gabby Gonzalez encountered five elementals in ancient China guarding the Red Jade General's walled village. They were personifications of the elemental forces of Earth (土), Water (水), Fire (火), Wood (木), and Metal (金). The Doctor was aware of these elements and learned more from Master Wu Wei's book. The Doctor organised Li and his friends to defeat the elementals. The Earth monster was dissolved in the Yellow River; the living Water storm was netted and smashed into rocks; the Fire woman was doused with water; the Wood monster was set on fire; and the bladed Metal man was pushed into a deep hole. (COMIC: Sharper Than a Serpent's Tooth)