Calcium

Discovery of calcium

Humans have been using calcium compounds for thousands of years, such as in cement, for example.

Limestone [calcium carbonate] was called calx by the Romans. The Romans heated the lime, removing the carbon to leave calcium oxide. To make cement, all they had to do was mix calcium oxide with water. The Romans built large amphitheaters and aqueducts using calcium oxide cement to bind the stones together.

Despite the long history of calcium compounds, the element itself was not discovered until electricity became available for use in experiments.

Calcium was first isolated by Sir Humphry Davy in 1808 in London. In a lecture to the Royal Society in June 1808, Davy described his experiments that year, which produced, at best, small amounts of metal. He could not find any way to produce more metallic calcium until a letter from Jöns Berzelius in Stockholm pointed him in the right direction.

Davy learned that Berzelius and Magnus Pontin had used a battery to decompose calcium oxide on a mercury electrode and had obtained an amalgam of mercury and calcium. (Berzelius, the great Swedish chemist, exchanged a great deal of information with Davy. He had learned before Davy that potassium could be dissolved in mercury to form an amalgam. Berzelius had expanded on the method).

Davy made a paste of slaked lime [calcium oxide, slightly moistened to form calcium hydroxide] and red oxide of mercury [mercury (II) oxide].

He made a depression in the paste and placed about 3.5 grams of metallic mercury there to act as an electrode. He used platinum as the counter electrode. Davy carried out the experiment under naphtha (a liquid hydrocarbon under which he had discovered that he could safely store potassium and sodium).

When electricity was passed through the paste, an amalgam of calcium and mercury formed on the mercury electrode.

Davy removed the mercury by distillation to reveal a new element: calcium.

Davy used the same procedure to isolate strontium, barium, and magnesium.

He named the metal calcium because of its presence in lime.

Interesting facts about calcium

• Calcium is the most abundant metallic element in the human body. The average adult body contains about 1 kg of calcium, 99% of which is found in bones and teeth. Only oxygen, carbon, hydrogen, and nitrogen are more abundant in our bodies than calcium.
• Calcium not only builds the structures that support our bodies, many of us also live in houses built with structural concrete or cement made with lime (calcium oxide). Snails and many shellfish use another calcium compound, calcium carbonate, to build their own houses too: their shells.
• Modern humans weren’t the first to use calcium to build things. The pyramids of Egypt were built with blocks of limestone. Limestone is crystalline calcium carbonate. In later pyramids, the blocks were held together with mortar made from gypsum or lime. Gypsum is calcium sulfate dihydrate, and lime is calcium oxide.
• Have you ever wanted to be “in the spotlight”? Lime is calcium oxide, which produces a bright, intense light when burned in an oxygen flame. It was used to light theater stages during the 19th century until electricity took over, hence the saying.
• Animal and plant cells must communicate with other cells. This is called signaling. Calcium ions are the most important messengers between cells in living organisms and are absolutely vital for the existence of multicellular life forms.

Appearance and Characteristics

Harmful effects:

Non-toxic and an essential metal for living organisms.

Characteristics:

• Calcium is reactive and, for a metal, soft. With a little effort, it can be cut with a sharp knife.
• When exposed to air, calcium develops a mixed layer of oxide and nitride, which protects it from further corrosion.
• Calcium reacts easily with water and acids, and the metal burns brightly in air, forming mainly nitride.

Uses of calcium

• Calcium forms alloys with aluminum, beryllium, copper, lead, and magnesium.
• It is used in the manufacture of other metals such as uranium and thorium.
• Calcium is used to remove oxygen, sulfur, and carbon from alloys.
• Calcium from limestone is a vital component of Portland cement.
• Quicklime (CaO) is used in many applications in the chemical industry, such as drinking water treatment, especially to soften water and remove arsenic, animal waste, and sewage.

Abundance and isotopes

• Abundance in the Earth’s crust: 4.2% by weight, 2.2% by mole
• Abundance in the solar system: 70 parts per million by weight, 2 parts per million by mole
• Cost of pure production: €20 per 100g
• Cost of bulk production: €1 per 100g
• Source: Calcium is found in nature in various minerals, including limestone (calcium carbonate), gypsum (calcium sulfate), and fluorite (calcium fluoride). Commercially, it can be manufactured by electrolysis of molten calcium chloride, CaCl₂. The pure metal can also be produced by replacing the calcium in lime (CaCO₃) with aluminum in hot autoclaves at low pressure.
• Isotopes: Calcium has 19 isotopes with known half-lives, with mass numbers from 35 to 53. Natural calcium is a mixture of six isotopes and is found in the percentages shown: 40 Ca (97%), 42 Ca (0.6%), 43 Ca (0.1%), 44 Ca (2%), 46 Ca (0.004%), and 48 Ca (0.2%).

Symbol	Ca
Atomic number	20
Valence	+2
Atomic weight	40,08
Boiling point (ºC)	+1484
Melting point (ºC)	+842
Density (Kg/m3)	1550
Atomic structure	[Ar] 4s2

Discover more elements in our periodic table.