Hydrogen resembles the alkali metals in that it has only one electron in its outermost shell, making it highly reactive and capable of losing that electron to form a positive ion. Like the alkali metals, it can also form ionic compounds with non-metals such as chlorine, oxygen, and sulfur. Furthermore, hydrogen can form hydrides, which are analogous to the alkali metal hydrides, in which it donates its electron to another element (usually a metal). These hydrides are often used as reducing agents in chemical reactions, similar to the alkali metal hydrides.
