Calcium

What is Calcium?

Calcium is the chemical element or alkaline-earth metal of Group-2 (IIA) of the periodic table with the symbol Ca and atomic number 20. It is the essential element in the human body for building bones, clotting blood, contracting muscles, and beating our hearts. The electronic configuration of calcium suggests that the metal has two s-electrons available for chemical bonding and it shows a common oxidation number or state of +2. About 90 percent of the calcium in the human body is used to make our bones and teeth. It is a silvery-white, lustrous, and relatively hard metal than alkali metals.

Properties of Calcium

It is formed a face-centered cubic crystal lattice with a higher melting point than alkali metals.

It possesses a 4s² valence shell electronic configuration over the previous noble gas argon. The s² configuration leads to inclusion in Group-2 or IIA of the periodic table.

Some important properties of the metal are given below the table,

Properties of Calcium
Atomic number	20
Electron per shell	2, 8, 8, 2
Atomic weight	40.078
Electronic Configuration	[Ar] 4s2
Block	s-block
Period	4
Group	2
Melting point	842 °C, ​1548 °F
Boiling point	1484 °C, ​2703 °F
Molar heat capacity	25.929 J mol−1 K−1
Crystal structure	face-centered cubic (fcc)
Density	1.55 g/cm3
Common oxidation number or state	+2
Electronegativity	​1.00 ( Pauling scale)
Ionization energy (kJ/mol)	1st	2nd	3rd
	589.8	1145.4	4912.4

Calcium in the Periodic Table

Due to two electrons in the valence s-orbital, calcium was placed in the s-block of the periodic table with other group members beryllium, magnesium, strontium, barium, and radium.

Where is Calcium Found?

It is the fifth most abundant element (3.63 percent) in the earth’s crust. It is concentrated in minerals that are probably separated during the main stage of the crystallization of magma.

Weathering and leaching lead to the formation of minerals calcium carbonate (CaCO₃) or limestone in earth soil. The very low solubility of CaCO₃ is the most probable reason for the absence of a significant amount of Ca⁺² ion in sea-water.

Gypsum (CaSO₄, 2H₂O), fluorspar (CaF₂) and apatite [3Ca₃(PO₄)₂, CaF₂] are important minerals of calcium.

Sources of Calcium

Every day we lose calcium from our body through our skin, nails, hair, sweat, urine, and feces but our body cannot produce it. Therefore, we need to eat Ca-reached foods or vegetables that sustain the deficiency of Ca in our bodies.

Dairy products (milk, yogurt, cheese) and vegetables like green leaf, beans, broccoli, brussels sprouts, collards, kale, and mustard greens are the main sources of calcium for our daily requirements.

Isotopes of Ca

Naturally, occurring calcium is a mixture of five stable isotopes like ⁴⁰Ca, ⁴²Ca, ⁴³Ca, ⁴⁴Ca, and ⁴⁶Ca. The radioactive isotope ⁴⁸Ca (half-life of about 4.3 × 10¹⁹ years) can be considered stable.

It is the first lightest element that contains six naturally occurring isotopes.

Production Process

It is produced on a commercial scale by electrolysis of fused CaCl₂. Some fluorspar (CaF₂) was added due to the lower temperatures for fusion.

The electrolysis is carried out in a graphite pot serving as an electrode or anode. A water-cooled iron cathode hangs into the fused electrolyte.

The produced metal is deposited on the cathode in the form of a rod when the electrolysis proceeds. A layer of fused electrolyte protects the metal from oxidation.

Facts About Calcium

Grup-2 elements of the periodic table are characterized by two valence electrons in an s-shell of the atoms. These two electrons are always involved together to show the uniform bivalency of the metal.

The properties of elements like Ca, St, Ba, Ra, and their compounds are systematically and gradually changed with the increasing atomic number.

Electropositive or metallic character and ionic radius increase from calcium to radium. Thermal stabilities of carbonates, nitrate, and sulfates are also increased from Ca to Ra.

Chemical Compounds

Calcium Hydride

Calcium hydride is formed by ionic bonding due to the high electropositive character and large size of the metal. CaH₂ is a high melting crystalline solid, that conducts electricity in a fused state and liberates hydrogen on electrolysis.

The hydride is obtained by the direct combination of hydrogen with the metal. The reaction of CaH₂ with water provides a ready source of hydrogen.

Calcium Oxide

All the oxides of Grup-2 elements are ionic with a high melting point but beryllium oxide is formed by covalent bonding.

The tendency to form peroxide and superoxide increases with the increasing atomic number of the Group-2 elements. Calcium superoxide is formed by the reaction of metal peroxide with 30 percent hydrogen peroxide.

The oxides react with water to form hydroxides. The basic properties of Group-2 hydroxides increase from beryllium to barium.

Calcium Halide

All the crystalline halides of Ca are ionic in nature with a high melting point. CaF₂ is a high melting (melting point 1418 °C) water-insoluble solid while chloride is a lower melting point and water-soluble.

The bromide and iodide have still lower meting and are higher soluble in water and alcohol.

What is Calcium Used For?

• Due to a strong chemical affinity for oxygen and sulfur, metallic calcium is widely used for making steel.
• It is an important reducing agent for the production of chromium, zirconium, thorium, and uranium.
• It is used as a scavenger in the steel industry to remove oxygen, sulfur, and phosphorus.
• Calcium is used in aluminum alloying to improve the strength of the metal.
• It is used to remove nitrogen from argon.
• It is also used for manufacturing the chemical compound, hydrolith (CaH₂).

Function in the Human Body

About 90 percent of the metal in the human body is used to make our bones and teeth.

It not only plays a major structural role but also plays crucial regulatory functions like muscle construction, nerve transmission, and blood coagulation. The deficiency of calcium in the human body causes hypocalcemia, rickets, and osteoporosis.