Hydrogen is like the alkali metals in that it has only one outer electron. Hydrogen has unique properties and is usually considered, as a family by itself.
There are four ways in which the hydrogen atom can react.
1. A neutral hydrogen atom can/may lose it’s one electron to become a positively charged hydrogen ion. A positively charged hydrogen ion is simply a proton. A proton is about one trillionth the size of an atom. Because of its small size, the hydrogen ion has some unique properties/characteristics.
2. A hydrogen atom can react is by sharing its single outer electron. Most nonmetals react with hydrogen to form compounds involving shared electrons (form covalent compounds). HCl and H2
O are examples of these covalent compounds.
3. Hydrogen can react is to gain an electron. When/if this occurs, the hydrogen atom becomes a hydride ion, H-. This reaction can only take place between hydrogen and atoms of elements that give up electrons easily. Examples of these would be NaH, and LiH.
The most reactive metals are in groups Groups IA and IIA. They will form ionic hydrides.
The hydride ion is larger than the fluoride ion. The size/dimension of this radius indicates that the single proton of the hydride ion has a very weak hold on the two electrons. One would expect that the ionic hydrides would not be highly stable. Experiment confirms/bears out this conclusion.
Ionic hydrides are highly reactive compounds. Hydrogen attains the stable outer level configuration of helium by sharing or gaining electrons.
4. The fourth type of bonding involves the formation of bridges between two atoms by hydrogen atoms. Some examples of these compounds are found with the element boron (boranes, e.g., BH3
) and some of the transition metals. Hydrogen is very soluble in many compounds composed of transition metals and rare earth metals. Hydrogen is readily/easily dissolved in both crystalline and amorphous metals. The solubility of hydrogen in metals is affected by impurities and/or distortions in the crystal lattice of the metal.