20 potassium ← calcium → scandium
Mg ↑ Ca ↓ Sr
Periodic table - Extended periodic
Name, symbol, number
calcium, Ca, 20
alkaline earth metals
Group, period, block
2, 4, s
Standard atomic weight
40.078(4) g·mol −1
[Ar] 4s 2
Electrons per shell
2, 8, 8, 2
Density (near r.t.)
1.55 g·cm −3
Liquid density at m.p.
1.378 g·cm −3
1115 K (842 °C, 1548 °F)
1757 K (1484 °C, 2703 °F)
Heat of fusion
8.54 kJ·mol −1
Heat of vaporization
154.7 kJ·mol −1
(25 °C) 25.929 J·mol −1·K −1
cubic face centered
2 (strongly basic oxide)
1.00 (Pauling scale)
(more) 1st: 589.8 kJ·mol −1
2nd: 1145.4 kJ·mol −1
3rd: 4912.4 kJ·mol −1
Atomic radius (calc.)
(20 °C) 33.6 nΩ·m
(300 K) 201 W·m −1·K −1
(25 °C) 22.3 µm·m −1·K −1
Speed of sound (thin rod)
(20 °C) 3810 m/s
CAS registry number
Ca is stable with 20 neutrons
5 y ε
Ca is stable with 22 neutrons
Ca is stable with 23 neutrons
Ca is stable with 24 neutrons
15 y β
-β - ?
- 0.694, 1.99
19 y β
-β - ?
Calcium (pronounced ) is the chemical element in the
periodic table that has the symbol Ca and atomic number 20. It has an atomic
mass of 40.078. Calcium is a soft grey alkaline earth metal, and is the fifth
most abundant element in the Earth's crust. It is essential for living
organisms, particularly in cell physiology, and is the most common metal in many
animals. /ˈkælsiəm/ Characteristics
The most abundant isotope,
40Ca, has a nucleus of 20 protons and
20 neutrons. This is the heaviest stable isotope of any element which has equal
numbers of protons and neutrons. In supernova explosions, calcium is formed from
the reaction of carbon with various numbers of alpha particles (helium nuclei),
until the most common calcium isotope (containing 10 helium nuclei) has been
synthesized. Calcium is the seventh most common element, by mass, in Earth's
Chemically calcium is reactive and moderately soft for a metal (though harder
than lead, it can be cut with a knife with difficulty). It is a silvery metallic
element that must be be extracted by electrolysis from a fused salt like calcium
chloride. Once produced, it rapidly forms a grey-white oxide and nitride coating
when exposed to air. It is somewhat difficult to ignite, in character rather
like magnesium, but when lit, the metal burns in air with a brilliant
high-intensity red light. Calcium metal reacts with water, evolving hydrogen gas
at a rate rapid enough to be noticible (unlike its sister magnesium) but not
fast enough at room temperature to generate much heat. Part of the slowness of
the calcium-water reaction results from the metal being partly protected by
insoluble white calcium hydroxide. In water solutions of acids where the salt is
water soluble, calcium reacts vigorously.
Calcium salts are colorless from any contribution of the calcium, and ionic
solutions of calcium (Ca
2+) are colorless as well. Many calcium salts
are not soluble in water. When in solution, the calcium ion to the human taste
varies remarkably, being reported as mildly salty, sour, "mineral like" or even
"soothing." It is apparent that many animals can taste, or develop a taste, for
calcium, and use this sense to detect the mineral in salt licks or other
sources. In human nutrition, soluble calcium salts may be added to tart juices
without much effect to the average palate.
Calcium is the fifth most abundant element by mass in the human body, where
it is a common cellular ionic messenger with many functions, and serves also as
a structural element in bone. It is the relatively high atomic-numbered calcium
in the skeleton which causes bone to be radio-opaque. Of the human body's solid
components after drying (as for example, after cremation), about a third of the
total mass is the approximately one kilogram of calcium which composes the
average skeleton (the remainder being mostly phosphorus and oxygen).
Calcium is not naturally found in its elemental state. Calcium occurs most
commonly in sedimentary rocks in the minerals calcite, dolomite and gypsum. It
occurs in igneous and metamorphic rocks chiefly in the silicate minerals:
plagioclase, amphiboles, pyroxenes and garnets.
Some uses are:
as a reducing agent in the extraction of other metals, such as uranium,
zirconium, and thorium.
as a deoxidizer, desulfurizer, or decarbonizer for various ferrous and
as an alloying agent used in the production of aluminium, beryllium, copper,
lead, and magnesium alloys.
in the making of cements and mortars to be used in construction.
Calcium Carbonate (CaCO 3) used in manufacturing cement and
mortar, lime, limestone (usually used in the steel industry); aids in production
in the glass industry, also has chemical and optical uses as mineral specimens
in toothpastes for example.
Calcium hydroxide solution (Ca(OH) 2) (also known as limewater) is
used to detect the presence of carbon dioxide by being bubbled through a
solution. It turns cloudy where CO 2 is present.
Calcium arsenate (Ca 3(AsO 4) 2) is used in
Calcium carbide (CaC 2) is used: to make acetylene gas (for use in
acetylene torches for welding) and in the manufacturing of plastics.
Calcium chloride (CaCl 2) is used: in ice removal and dust control
on dirt roads, in conditioner for concrete, as an additive in canned tomatoes,
and to provide body for automobile tires.
(Ca(C 6H 11NHSO 4) 2) was used as a
sweetening agent but is no longer permitted for use because of suspected
Calcium gluconate (Ca(C 6H 11O 7) 2)
is used as a food additive and in vitamin pills.
Calcium hypochlorite (Ca(OCl) 2) is used: as a swimming pool
disinfectant, as a bleaching agent, as an ingredient in deodorant, and in
algicide and fungicide.
Calcium permanganate (Ca(MnO 4) 2) is used in liquid
rocket propellant, textile production, as a water sterilizing agent and in
Calcium phosphate (Ca 3(PO 4) 2) is used as a
supplement for animal feed, fertilizer, in commercial production for dough and
yeast products, in the manufacture of glass, and in dental products.
Calcium phosphide (Ca 3P 2) is used in fireworks,
rodenticide, torpedoes and flares.
Calcium stearate (Ca(C 18H 35O 2) 2
is used in the manufacture of wax crayons, cements, certain kinds of plastics
and cosmetics, as a food additive, in the production of water resistant
materials and in the production of paints.
Calcium sulfate (CaSO 4·2H 2O) is used as common
blackboard chalk, as well as, in its hemihydrate form being more well known as
Plaster of Paris.
Calcium tungstate (CaWO 4) is used in luminous paints, fluorescent
lights and in X-ray studies.
H and K lines
In the visible portion of the spectrum of many stars, including the Sun, show
strong absorption lines of singly-ionized Calcium. Prominent among these are the
H-line at 3968.5 Å and the K line at 3933.7 Å of singly-ionized
Calcium, or Ca II. For the Sun and stars with low temperatures, the
prominence of the H and K lines can be an indication of strong magnetic activity
in the chromosphere. Measurement of periodic variations of these active regions
can also be used to deduce the rotation periods of these stars.
calx, meaning "limestone") was known as early as the
first century when the Ancient Romans prepared lime as calcium oxide. It was not
isolated until 1808 in England when Sir Humphry Davy electrolyzed a mixture of
lime and mercuric oxide. Davy was trying to isolate calcium; when he heard that
Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury,
he tried it himself. He worked with electrolysis throughout his life and also
discovered/isolated sodium, potassium, magnesium, boron and barium.
Other compounds include Calcium carbonate (CaCO
3), one of the
common compounds of calcium. It is heated to form quicklime (CaO), which is then
added to water (H 2O). This forms another material known as slaked
lime (Ca(OH) 2), which is an inexpensive base material used throughout
the chemical industry. Chalk, marble, and limestone are all forms of calcium
Calcium, combined with phosphate to form hydroxylapatite, is the mineral
portion of human and animal bones and teeth. The mineral portion of some corals
can also be transformed into hydroxylapatite.
Calcium oxide (lime) is used in many chemical refinery processes and is made
by heating and carefully adding water to limestone. When lime is mixed with
sand, it hardens into a mortar and is turned into plaster by carbon dioxide
uptake. Mixed with other compounds, lime forms an important part of Portland
When water percolates through limestone or other soluble carbonate rocks, it
partially dissolves part of the rock and causes cave formation and
characteristic stalactites and stalagmites and also forms hard water. Other
important calcium compounds are nitrate, sulfide, chloride, carbide, cyanamide,
Calcium has four stable isotopes (
40Ca and 42Ca through
44Ca), plus two more isotopes ( 46Ca and 48Ca)
that have such long half-lives that for all practical purposes they can be
considered stable. It also has a cosmogenic isotope, radioactive
41Ca, which has a half-life of 103,000 years. Unlike cosmogenic
isotopes that are produced in the atmosphere, 41Ca is produced by
neutron activation of 40Ca. Most of its production is in the upper
metre or so of the soil column, where the cosmogenic neutron flux is still
sufficiently strong. 41Ca has received much attention in stellar
studies because it decays to 41K, a critical indicator of
97% of naturally occurring calcium is in the form of
40Ca is one of the daughter products of 40K decay, along
with 40Ar. While K-Ar dating has been used extensively in the
geological sciences, the prevalence of 40Ca in nature has impeded its
use in dating. Techniques using mass spectrometry and a double spike isotope
dilution have been used for K-Ca age
Zookeeper - 2007-12-08 04:29:51