Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air, its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium; the most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life. The name derives from Latin calx "lime", obtained from heating limestone; some calcium compounds were known to the ancients, though their chemistry was unknown until the seventeenth century. Pure calcium was isolated in 1808 via electrolysis of its oxide by Humphry Davy, who named the element. Calcium compounds are used in many industries: in foods and pharmaceuticals for calcium supplementation, in the paper industry as bleaches, as components in cement and electrical insulators, in the manufacture of soaps.

On the other hand, the metal in pure form has few applications due to its high reactivity. Calcium is the fifth-most abundant element in the human body; as electrolytes, calcium ions play a vital role in the physiological and biochemical processes of organisms and cells: in signal transduction pathways where they act as a second messenger. Calcium ions outside cells are important for maintaining the potential difference across excitable cell membranes, protein synthesis, bone formation. Calcium is a ductile silvery metal whose properties are similar to the heavier elements in its group, strontium and radium. A calcium atom has twenty electrons, arranged in the electron configuration 4s2. Like the other elements placed in group 2 of the periodic table, calcium has two valence electrons in the outermost s-orbital, which are easily lost in chemical reactions to form a dipositive ion with the stable electron configuration of a noble gas, in this case argon. Hence, calcium is always divalent in its compounds, which are ionic.

Hypothetical univalent salts of calcium would be stable with respect to their elements, but not to disproportionation to the divalent salts and calcium metal, because the enthalpy of formation of MX2 is much higher than those of the hypothetical MX. This occurs because of the much greater lattice energy afforded by the more charged Ca2+ cation compared to the hypothetical Ca+ cation. Calcium, strontium and radium are always considered to be alkaline earth metals. Beryllium and magnesium differ from the other members of the group in their physical and chemical behaviour: they behave more like aluminium and zinc and have some of the weaker metallic character of the post-transition metals, why the traditional definition of the term "alkaline earth metal" excludes them; this classification is obsolete in English-language sources, but is still used in other countries such as Japan. As a result, comparisons with strontium and barium are more germane to calcium chemistry than comparisons with magnesium.

Calcium metal melts at 842 °C and boils at 1494 °C. It crystallises in the face-centered cubic arrangement like strontium, its density of 1.55 g/cm3 is the lowest in its group. Calcium can be cut with a knife with effort. While calcium is a poorer conductor of electricity than copper or aluminium by volume, it is a better conductor by mass than both due to its low density. While calcium is infeasible as a conductor for most terrestrial applications as it reacts with atmospheric oxygen, its use as such in space has been considered; the chemistry of calcium is that of a typical heavy alkaline earth metal. For example, calcium spontaneously reacts with water more than magnesium and less than strontium to produce calcium hydroxide and hydrogen gas, it reacts with the oxygen and nitrogen in the air to form a mixture of calcium oxide and calcium nitride. When finely divided, it spontaneously burns in air to produce the nitride. In bulk, calcium is less reactive: it forms a hydration coating in moist air, but below 30% relative humidity it may be stored indefinitely at room temperature.

Besides the simple oxide CaO, the peroxide CaO2 can be made by direct oxidation of calcium metal under a high pressure of oxygen, there is some evidence for a yellow superoxide Ca2. Calcium hydroxide, Ca2, is a strong base, though it is not as strong as the hydroxides of strontium, barium or the alkali metals. All four dihalides of calcium are known. Calcium carbonate and calcium sulfate are abundant minerals. Like strontium and barium, as well as the alkali metals and the divalent lanthanides europium and ytterbium, calcium metal dissolves directly in liquid ammonia to give a dark blue solution. Due to the large size of the Ca2+ ion, high coordination numbers are common, up to 24 in some intermetallic compounds such as CaZn13. Calcium is complexed by oxygen chelates such as EDTA and polyphosphates, which are useful in

Mary Beth Marley

Mary Beth Marley is an American pair skater. With former partner Rockne Brubaker, she is the 2012 Four Continents bronze medalist and 2012 U. S. silver medalist. Marley competed in single skating and became the 2009 U. S. novice silver medalist. Marley won the novice silver medal at the 2009 U. S. Championships, she was 5th on the junior level in 2011. Marley and Brubaker teamed up after a two-day tryout in August 2010, she was a singles skater and had no pairs experience but passed her pairs test on August 31, 2010. The pair was coached by John Nicks. Marley relocated to California. Marley and Brubaker's first international competition was the Toruń Cup in Toruń, where they earned the minimum technical scores required to compete at an ISU Championship, they placed fourth at the 2011 U. S. Nationals and were named as alternates for Four Continents, they were assigned to the event after an injury led Caydee Jeremy Barrett to withdraw. Jenni Meno and Todd Sand became their main coaches for the 2011–12 season and Nicks continued to work with the pair.

In the 2012–2013 season and Brubaker were assigned to 2012 Skate Canada International and 2012 NHK Trophy, however, on August 14, 2012, the pair announced the end of their partnership. Marley decided to step away from competitive figure skating She works as a coach and choreographer in Chicago. Mary Beth Marley / Rockne Brubaker at the International Skating Union Mary Beth Marley / Rockne Brubaker at Ice Network Mary Beth Marley at Ice Network

Ernest Hillas Williams

Sir Ernest Hillas Williams was an Irish judge who served as a British Empire colonial official based for most of his career in British Hong Kong and also the second Chief Justice of the Combined Judiciary of Sarawak, North Borneo and Brunei. Whilst serving in the Colonial Service, Williams was promoted from colonial administrator to puisne judge and also served as the assistant Attorney General of Hong Kong. Over the course of his time in British Hong Kong, Williams was twice appointed acting Secretary for Chinese Affairs of the Executive Council of Hong Kong. Following the events of World War II, Williams was sent to British Borneo and succeeded Sir Ivor Llewellyn Brace as Chief Justice of the Combined Judiciary of Sarawak, North Borneo and Brunei. Williams was a sergeant in the Hong Kong Volunteer Defence Corps. Williams was a prisoner of war held at a camp in Sham Shui Po Barracks before being moved to Innoshima, Hiroshima Prefecture by the Imperial Japanese Army. United Kingdom: Knight Bachelor - Sir Williams died in early February 1965 whilst in the town of Málaga, Spain.

Chief Judge of Sabah and Sarawak Secretary for Justice