Alkaline earth metals, the elements in the second column of the periodic table, are the most likely elements to lose two electrons in chemical reactions. They include beryllium, magnesium, calcium, strontium, barium and radium. It is important to note, however, that beryllium varies greatly from the other alkaline earth metals, and despite having only two electrons in its outer valence shell, it does not readily lose electrons in reactions.
Alkaline earth metals share the feature of having only two electrons in an outer valence shell with the capacity for eight. This highly incomplete outer shell is unstable, and most of these metals lose both electrons easily when encountering electronegative elements such as oxygen or halogen gases. Such reactions typically create ionic compounds. Calcium carbonate, for instance, is a common ionic compound, and is the main constituent of limestone. Calcium and magnesium compounds are also common and are essential to life.
Beryllium is an exception to several typical features of this group. It is the first element in the group, with the lowest atomic number and mass. Alkaline earth metals typically react strongly with water or steam, forming powerful hydroxide bases. Beryllium does not. Beryllium forms covalent bonds with non-metals, rather than ionic bonds like other alkaline earth metals.