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
widely used in many industries: in foods and pharmaceuticals for calcium
supplementation, in the paper industry as bleaches, as components in cement and
electrical insulators, and in the manufacture of soaps. On the other hand, the
metal in pure form has few applications due to its high reactivity; still, in
small quantities it is often used as an alloying component in steelmaking, and
sometimes, as a calcium–lead alloy, in making automotive batteries.
Calcium is the most
abundant metal and the fifth-most abundant element in the human body. As electrolytes, calcium ions ( Ca2+) 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; in neurotransmitter release from neurons;
in contraction of all muscle cell types; as cofactors in
many enzymes; and in fertilization. Calcium ions outside cells
are important for maintaining the potential difference across
excitable cell membranes, protein synthesis, and bone formation.
Classification
Calcium is a very ductile silvery metal
(sometimes described as pale yellow) whose properties are very similar to the heavier
elements in its group, strontium, barium, and radium. A calcium
atom has 20 electrons, with electron configuration [AR] 4s2 . Like the other elements in group 2
of the periodic table, calcium has two valence electrons in the
outermost s-orbital, which are very 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 almost always divalent in its
compounds, which are usually 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 highly charged Ca2+ cation compared to the
hypothetical Ca+ cation. Calcium, strontium,
barium, and radium are always considered to be alkaline earth metals; the
lighter beryllium and magnesium, also in group 2 of the periodic
table, are often included as well. Nevertheless, beryllium and magnesium differ
significantly from the other members of the group in their physical and
chemical behavior: they behave more like aluminium and zinc respectively
and have some of the weaker metallic character of the post-transition
metals, which is why the traditional definition of the term "alkaline
earth metal" excludes them.
Physical properties
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Calcium
is harder than lead but 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 very low density. While
calcium is infeasible as a conductor for most terrestrial applications as it
reacts quickly with atmospheric oxygen, its use as such in space has been
considered.
Chemical properties
The
chemistry of calcium is that of a typical heavy alkaline earth metal. For
example, calcium spontaneously reacts with water more quickly than magnesium
but less quickly than strontium to produce calcium hydroxide and
hydrogen gas. It also reacts with the oxygen and nitrogen in
air to form a mixture of calcium oxide and calcium nitride. When
finely divided, it spontaneously burns in air to produce the nitride. Bulk
calcium is less reactive: it quickly 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, calcium peroxide, CaO2, can be made by direct
oxidation of calcium metal under a high pressure of oxygen, and there is some
evidence for a yellow superoxide Ca( O 2 )2.Calcium hydroxide,
Ca(OH)2, is a strong base, though not as strong as the hydroxides of
strontium, barium or the alkali metals. All four dihalides of calcium are
known. Calcium carbonate ( CaCO3) and calcium
sulfate (CaSO4) are particularly 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.
Organocalcium
compounds
In
contrast to organomagnesium compounds, organocalcium compounds are not
similarly useful, with one major exception, calcium carbide, CaC2. This material, which
has historic significance, is prepared by heating calcium oxide with carbon.
According to X-ray crystallography, calcium carbide can be described as Ca2+ derivative of
acetylide, C2 2-, although it is not a salt. Several
million tons of calcium carbide are produced annually. Hydrolysis gives acetylene,
which is used in welding and a chemical precursor. Reaction with nitrogen gas
converts calcium carbide to calcium cyanamide.
A
dominant theme in molecular organocalcium chemistry is the large radius of
calcium, which often leads to high coordination numbers. For example,
dimethyl calcium appears to be a 3-dimensional polymer, whereas dimethyl
magnesium is a linear polymer with tetrahedral Mg centers. Bulky
ligands are often required to disfavor polymeric species. For example,
calcium dicyclopentadienyl, Ca (C5 H )2 has a polymeric
structure and thus is nonvolatile and insoluble in solvents. Replacing
the CH5 ligand with the bulkier C5 (CH3 )5 (pentamethylcyclopentadienyl)
gives a soluble complex that sublimes and forms well-defined adducts with
ethers. Organocalcium compounds tend to be more similar to organoytterbium
compounds due to the similar ionic radii of Yb 2+ (102 pm) and
Ca2+ (100 pm).
Organocalcium
compounds have been well investigated. Some such complexes exhibit catalytic
properties, although none have been commercialized.
Yes, calcium
is crucial for the human body, supporting the formation of strong bones and
teeth, enabling muscle contraction and nerve signal transmission, and playing a
key role in blood clotting, heart function, and hormone secretion. Because the
body can’t produce calcium, it must be obtained through diet, with dairy
products, fortified foods, and leafy green vegetables beings excellent sources.
Functions of Calcium
·
Bone and Teeth
Health: Approximately
99% of the body's calcium is in bones and teeth, providing structure and
strength.
·
Nerve Function: Calcium transmits nerve signals,
allowing the brain to send messages to other parts of the body.
·
Muscle
Contraction: It facilitates
the squeezing and relaxing of muscles, which is essential for movement.
·
Heart Function: Calcium helps maintain a regular heart
rate and is involved in the relaxation and contraction of blood vessels.
·
Hormone
Secretion: It plays a
role in the release of hormones and other chemicals necessary for various
bodily functions.
·
Blood Clotting: Calcium is necessary for the blood to
clot, which is a vital process to stop bleeding after an injury.
Why Calcium Intake is
Important
·
Prevents
Osteoporosis: A proper level
of calcium throughout life helps prevent osteoporosis, a condition where
bones become weak and brittle.
·
Body's
Reservoir: Bones act as a
calcium reservoir; if dietary calcium is insufficient, the body can draw
calcium from the bones, weakening them over time.
·
Daily Loss: The body constantly loses calcium
through various processes, so regular dietary intake is necessary to replenish
it.
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