beryllium did form compounds with an ionization state of +2, it would polarize electron clouds that are near it very strongly and would cause extensive orbital overlap, since beryllium has a high charge density. All compounds that include beryllium have a covalent bond. Even the compound beryllium fluoride, which is the most ionic beryllium compound, has a low melting point and a low electrical conductivity when melted. All the alkaline earth metals have two electrons in their valence shell, so the energetically preferred state of achieving a filled electron shell is to lose two electrons to form doubly charged positive ions. Compounds and reactions The alkaline earth metals all react with the halogens to form ionic halides, such as calcium chloride (), as well as reacting with oxygen to form oxides such as strontium oxide (). Calcium, strontium, and barium react with water to produce hydrogen gas and their respective hydroxides (magnesium also reacts, but much more slowly), and also undergo transmetalation reactions to exchange ligands. {| class="wikitable sortable" |+ Alkaline earth metals fluorides solubility-related constants ! Metal ! M2+HE ! F−HE ! "MF2"unitHE ! MF2latticeenergies ! Solubility |- | Be | 2,455 | 458 | 3,371 | 3,526 | soluble |- | Mg | 1,922 | 458 | 2,838 | 2,978 | 0.0012 |- | Ca | 1,577 | 458 | 2,493 | 2,651 | 0.0002 |- | Sr | 1,415 | 458 | 2,331 | 2,513 | 0.0008 |- | Ba | 1,361 | 458 | 2,277 | 2,373 | 0.006 |} Physical and atomic The table below is a summary of the key physical and atomic properties of the alkaline earth metals. Nuclear stability Of the six alkaline earth metals, beryllium, calcium, barium, and radium have at least one naturally occurring radioisotope; magnesium and strontium do not. Beryllium-7, beryllium-10, and calcium-41 are trace radioisotopes; calcium-48 and barium-130 only decay by double beta decay and have very long half-lives (longer than the age of the universe) and are thus primordial radionuclides; and all isotopes of radium are radioactive. Calcium-48 is the lightest nuclide to undergo double beta decay. Calcium and barium are weakly radioactive: calcium contains about 0.1874% calcium-48, and barium contains about 0.1062% barium-130. The longest lived isotope of radium is radium-226 with a half-life of 1600 years; it and radium-223, -224, and -228 occur naturally in the decay chains of primordial thorium and uranium. Beryllium-8 is