Calcium (Ca, Latin for calcium; this name comes from the Latin noun calx – lime, which means “metal from lime”) – a chemical element from the group of beryllium (alkaline earth metals) in the periodic table.

Characteristic
Calcium is a silvery white metal. In the air, it quickly covers with a layer of CaO oxide, so it must be stored without its access, e.g. in kerosene, like sodium and potassium. Metallic calcium has a hardness similar to lead, it can be cut with a knife, but added to other soft metals significantly increases their hardness.
The standard potential of the Ca2 + / Ca system is −2.86 V. Calcium reacts with water and with diluted inorganic (hydrochloric, nitric, harder sulfuric – poorly soluble CaSO4) and organic (e.g. acetic) acids, while the reactions with acids are more turbulent.
The most important calcium compounds are calcium oxide, calcium peroxide, calcium hydroxide and many salts, for example calcium carbonate, calcium nitrate or calcium carbide.
Ca2 + cations belong to the IV group of cations and stain the flame brick red.

Occurrence
Calcium occurs in the upper layers of the Earth in an amount of 3.54%. The main minerals and rocks are calcite, aragonite, marbles, chalk, limestone, gypsum, anhydrite, dolomite, fluorite, apatite and many silicates.
Stable calcium isotopes are 40Ca, 42Ca, 43Ca, 44Ca, 46Ca and 48Ca.

Discovery
Calcium and its compounds have been known since antiquity. Antoine Lavoisier already in 1789 guessed that there was some metallic element in calcium, but in his time no method of its separation was known. It wasn’t until Humphry Davy in 1808 that he isolated it pure and analytically proved it to be an element. Davy moistened the lime, added some mercury oxide to it, and formed it into a bowl, which he placed on the platinum plate, which is an anode. He filled the bowl with mercury, into which he dipped a platinum wire – a cathode on which metal was separated. After evaporating the mercury, a silver metal (calcium) remained. Michael Faraday used a new, simpler method. Namely, he electrolysed dry molten calcium chloride CaCl2. Metallic calcium was evolved at the cathode, but because it was lighter than molten calcium chloride, it floated to the surface of the liquid and burned. Only after this difficulty was removed, did Robert Bunsen and Mathiessen receive some amount of metallic calcium in this method in 1854–1855. Henri Moissan received relatively pure calcium in 1898 by electrolysis of molten calcium iodide.

Receiving
Currently, metallic calcium is obtained mainly by the improved Faraday method, i.e. by electrolysis of molten calcium chloride (also fluoride) or by calcining calcium oxide with aluminum without air access:

3CaO + 2Al → Al2O3 + 3Ca

Application
Metallic calcium has limited use as a protective agent against oxidation, e.g. in the production of copper, steel and nickel, from which it simultaneously removes sulfur. It is also used for purifying and drying oil, gasoline, alcohols, noble gases and others. It is also used to reduce uranium, thorium, rare earth oxides and others. to metallic form.

The use of calcium compounds:

• sulfate (gypsum – dihydrate, anhydrite – anhydrous) – construction, art, stiffening limbs in injuries, saturated aqueous solution (gypsum water) is used to distinguish calcium from strontium and barium in the course of qualitative analysis;
• nitrate – artificial fertilizers;
• carbide (carbide) – acetylene production;
• cyanamide – herbicide, fertilizer;
• chloride – cooling mixtures, deicing of roads, anhydrous – drying of substances, food additive;
• oxide (quicklime) – construction (plasters, mortars);
• hydroxide (slaked lime) – a saturated aqueous solution (lime water) is used to detect carbon dioxide and carbonates.

Biological significance
Calcium is part of the bones and some types of cell walls.
The total calcium content in the human body is 1.4-1.66% of body weight, of which 99% occurs in the form bound in bone (hydroxyapatite), while the remaining part occurs in the ionized form in intracellular and extracellular fluid and performs a number of important functions:

• enzyme activator;
• secondary relay – protein kinases;
• conduction of bioelectric impulses;
• participation in blood clotting;
• participation in skeletal, smooth muscle and heart muscle contraction;
• participation in inflammation, regeneration and proliferation reactions;
• participation in the secretion of animal hormones and neurotransmitters and exocrine glands;
• reduces the degree of hydration of cell colloids.

The level of calcium in the blood serum depends on:

• the amount of calcium in your food;
• the degree of calcium absorption in the gastrointestinal tract;
• the degree of urinary calcium excretion
The main hormones that affect calcium homeostasis are: parathyroid hormone, calcitonin and 1α, 25 (OH) 2-vitamin D.

Recommended daily calcium intake is:

Children and youth:

• 1-6 months 210 mg;
• 6 to 12 months: 270 mg;
• from 1 to 3 years: 500 mg;
• from 4 to 8 years: 800 mg;
• from 9 to 18 years: 1500 mg.

Adults

• from 19 to 50 years: 1200 mg;
• from 51 years and up: 1500 mg;

or

• for adults: 800 mg;
• for the elderly: 600 mg;
• for pregnant women: 1,400 mg;
• for lactating women: 2,000 mg.

Symptoms of calcium deficiency (hypocalcaemia):

A decrease in serum calcium levels is called hypocalcaemia. The effect of hypocalcemia is:

• bone fragility;
• decaying teeth;
• excessive muscle excitability to contraction (tetany – overt or latent);
• muscle pain;
• tingling and numbness of the limbs;
• blood coagulation disorders;
Heart arythmia;
• nosebleeds;
• hypotension;
• depression and anxiety;
• osteoporosis.

Symptoms of excess calcium (hypercalcaemia)

• constipation;
• nausea;
• lack of appetite.

This can lead to kidney stones and reduce the absorption of zinc and iron.

Homeostatic mechanisms try to restore the normal level of calcium in the blood serum by moving it from the reserve pool, and if this is not enough or the depletions are depleted – from the skeleton.

Calcium is also an essential component of plant cells. Its deficiency can cause tomato apical rot. Other symptoms of deficiency in plants:

• distribution of plasma membranes;
• abnormal height;
• necrosis of plant organs.