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Alkaline earth metal
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<table><tbody><tr><th colspan="2">↓ <a href="/facts/Period_(periodic_table)/WpGUFh5V">Period</a></th></tr><tr><th><a href="/facts/Period_2_element/1ajRWfrb">2</a></th><td><a href="/facts/Beryllium/dv295voP">Beryllium</a> (Be)4 </td></tr><tr><th><a href="/facts/Period_3_element/1BE0Nc0K">3</a></th><td><a href="/facts/Magnesium/XyIhd2FG">Magnesium</a> (Mg)12 </td></tr><tr><th><a href="/facts/Period_4_element/BgDFfE26">4</a></th><td><a href="/facts/Calcium/hf252CC0">Calcium</a> (Ca)20 </td></tr><tr><th><a href="/facts/Period_5_element/xLJUWWDS">5</a></th><td><a href="/facts/Strontium/ABaA5qQK">Strontium</a> (Sr)38 </td></tr><tr><th><a href="/facts/Period_6_element/9YleCXwf">6</a></th><td><a href="/facts/Barium/IkL09XHQ">Barium</a> (Ba)56 </td></tr><tr><th><a href="/facts/Period_7_element/H5QuVHGQ">7</a></th><td><a href="/facts/Radium/VWo5gkzn">Radium</a> (Ra)88 </td></tr><tr><td colspan="2"><p><i>Legend</i></p><table><tbody><tr><td><a href="/facts/Primordial_element/lFAUqHDv">primordial element</a></td></tr><tr><td><a href="/facts/Radioactive_decay/Ya6FVjt4">element by radioactive decay</a></td></tr></tbody></table></td></tr></tbody></table> <p>The alkaline earth metals are six <a href="/facts/Chemical_element/0jducgWD">chemical elements</a> in <a href="/facts/Group_(periodic_table)/YGBcUabv">group</a> 2 of the <a href="/facts/Periodic_table/umdGIfUb">periodic table</a>. They are <a href="/facts/Beryllium/dv295voP">beryllium</a> (Be), <a href="/facts/Magnesium/XyIhd2FG">magnesium</a> (Mg), <a href="/facts/Calcium/hf252CC0">calcium</a> (Ca), <a href="/facts/Strontium/ABaA5qQK">strontium</a> (Sr), <a href="/facts/Barium/IkL09XHQ">barium</a> (Ba), and <a href="/facts/Radium/VWo5gkzn">radium</a> (Ra). The elements have very similar properties: they are all shiny, silvery-white, somewhat <a href="/facts/Reactivity_(chemistry)/PuJ2pmRT">reactive</a> <a href="/facts/Metal/PT8hNX6R">metals</a> at <a href="/facts/Standard_temperature_and_pressure/JhJv9KFJ">standard temperature and pressure</a>. </p><p>Together with <a href="/facts/Helium/yRul93TG">helium</a>, these elements have in common an outer <a href="/facts/Atomic_orbital/tKhgl6mL">s orbital</a> which is full—that is, this orbital contains its full complement of two electrons, which the alkaline earth metals readily lose to form <a href="/facts/Cation/wrbwhF3z">cations</a> with <a href="/facts/Electric_charge/xxsBfmlB">charge</a> +2, and an <a href="/facts/Oxidation_state/W53W6s6V">oxidation state</a> of +2. Helium is grouped with the <a href="/facts/Noble_gas/j0yHMEAE">noble gases</a> and not with the alkaline earth metals, but it is theorized to have some similarities to beryllium when forced into bonding and has sometimes been suggested to belong to group 2. </p><p>All the discovered alkaline earth metals occur in nature, although radium occurs only through the <a href="/facts/Decay_chain/JvTwPNBn">decay chain</a> of <a href="/facts/Uranium/n2sGWBzU">uranium</a> and <a href="/facts/Thorium/ysdWH470">thorium</a> and not as a primordial element. There have been experiments, all unsuccessful, to try to synthesize <a href="/facts/Unbinilium/gUvSSHzd">element 120</a>, the next potential member of the group. </p>