The element calcium follows the trend in properties that is seen with magnesium and sodium and potassium elements. Namely, it is toxic to mammals in its metallic form, while it is unharmful in its ionic form. Actually, calcium ion is not only unharmful but also is essential for the metabolism of the body.
Calcium ions are required for the construction and building of bone tissue. It is also important for the proper functioning of the hormone insulin. Its concentration in the blood is controlled by two hormones. These are parathyroid hormone and calcitonin.
Parathyroid hormone is secreted by the parathyroid gland and it stimulates the release of calcium ions into the blood. Calcitonin, on the other hand stimulates the deposition of calcium ions to bone tissue. Therefore, we see the importance of calcium ions by the number of hormones that the body uses to regulate its function.
Calcium is next to sodium in the periodic table. In addition, it has the electronic configuration of sodium plus an additional electron in the 3s orbital. It has the electronic configuration of neon plus two additional electrons in the 3s orbital.
Neon is a noble gas which is inert at room temperature. Therefore, calcium metal is reactive due to the existence of the two additional electrons in the 3s orbital. It therefore tends to loose these electrons easily in order to achieve the electronic configuration of neon.
Calcium is more reactive than magnesium. This is due to the higher energy of the 2 electrons in the 3s orbital of calcium, in contrast to the 2 electrons of magnesium which reside in the 2s orbital. This 2s orbital is energetically lower than the 3s orbital of calcium.
The ionic diameter of the calcium ion is 200 pm which is comparable in value to that of sodium ion. The sodium ion has an ionic diameter of 204 pm. This proximity in ionic diameter values makes the chemistry of both of these elements similar to each other.
It is important to note here that this phenomenon is called in chemistry the diagonal relation between elements in the periodic table. It is a general trend for elements of the periodic table.
Crown ethers can dissolve calcium ions in organic solvents cannot dissolve it. Due to its positive charge non-polar organic solvents are especially not capable of dissolving alkaline earth ionic metals nor alkali metals ions.
Calcium has many compounds that are produced on a commercial basis. Calcium carbonate or CaCO3 in the form of limestone is the most important row material of calcium. CaCO3 occurs also in other minerals such as chalk and marble and calcite. CaCO3 is used to generate calcium oxide CaO. By heating CaCO3 to elevated temperature it gives CaO and CO2.
CaO is a base while CO2 is an acid. The combination of an acid an a base in inorganic chemistry usually gives salt. Calcium metal is generated by the electrolysis process of the halide of calcium.
Another compound of calcium is calcium hydroxide. It is used in paper industry and in pulp industry. Organic compounds of calcium are more reactive than their counterparts of magnesium. Strontsium and barium compounds are more reactive than that of calcium.
Calcium forms ionic compounds with all non metals such as the halogens and chalcogens. The reactivity of calcium column in the periodic table increases as we go down the periodic table. Thus, while magnesium is less reactive than calcium one observes that strontsium and barium are more reactive than calcium.
This trend in reactivity is ascribed to the higher energy of the loosely bound 2 electrons in the outermost s orbital of these metals