Calcium

OverviewCalcium is an alkaline earth metal. The alkaline earth metals make upGroup 2 (IIA) of the periodic table, a chart that shows how the elementsare related. They also include beryllium,magnesium, strontium, barium,and radium. The alkaline earth metals are more chemically active thanmost metals. Only the alkali metals in Group I (IA) are more reactive.

Calcium compounds are common and abundant in Earth’s crust.Humans have used calcium compounds for thousands of years in con-struction, sculpture, and roads.

Calcium metal was not prepared in a pure form until 1808 whenEnglish chemist Humphry Davy (1778–1829) passed an electric currentthrough molten (melted) calcium chloride.

Metallic calcium has relatively few uses. However, calcium com-pounds are well known and widely used. They include chalk, gypsum,limestone, marble, and plaster of paris.

Discovery and NamingIt is impossible to say when humans first knew about or used compoundsof calcium. Whenever they used limestone to build a structure, they were

Key Facts

Symbol: Ca

Atomic Number: 20

Atomic Mass: 40.078

Family: Group 2 (IIA);alkaline earth metal

Pronunciation: CAL-cee-um

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using a compound of calcium. Limestone is the common name for cal-cium carbonate (CaCO3). Whenever humans built a statue or monu-ment out of marble, they were using calcium carbonate in anotherform. Ancient Egyptians and early Greeks used mortar, a cement-likematerial that holds stones and bricks together. Early mortar was made

by roasting or heating limestone for long periodsof time. Water was then mixed with the powder,which would then dry to form a strong bond.

Another calcium compound used by earlycivilizations was plaster of paris. Plaster of parisis made by heating gypsum, or calcium sulfate(CaSO4), to remove the water that makes it crys-tallize. Water was added and it hardened into abrittle, cement-like substance. Until recently, itwas most often used to make casts to protectbroken bones. However, it has largely beenreplaced by fiberglass, which is lighter, yetstronger. The first mention of plaster of paris toprotect broken bones can be found in a bookwritten by Persian pharmacist Abu MansurMuwaffaw in about 975 CE.

By the 1700s, chemists had learned a greatdeal about calcium compounds. They knew thatlimestone, gypsum, marble, and many othercommonly occurring compounds all contain a

W O R D S T O K N O W

Alkaline earth metal: An element found inGroup 2 (IIA) of the periodic table.

Alloy: A mixture of two or more metals with prop-erties different from those of the individual metals.

Calx: The original term for calcium.

Isotopes: Two or more forms of an element thatdiffer from each other according to their massnumber.

Periodic table: A chart that shows how the che-mical elements are related to each other.

Quarry: A large hole in the ground from whichuseful minerals are taken.

Radioactive isotope: An isotope that breaks apartand gives off some form of radiation.

Tracer: A radioactive isotope whose presence in asystem can easily be detected.

Humphry Davy. LIBRARY OF

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common element. They called the element calx. That word comes fromthe Latin term for lime. In 1807, Davy isolated the new element.

Davy invented a method for extracting elements from compounds thatwere difficult to separate by usual methods. He first passed an electric cur-rent through the compound, causing it to melt. The electric current thencaused the compound to break apart into the elements of which it is made.

One of the compounds he used this method on was calx (calcium oxide;CaO), producing pure calcium metal for the first time. Davy suggestedthe name calcium for the new element. He chose the name by adding the

Element Discoverer: Humphry Davy

Born in 1778, Humphry Davy grew up in Corn-wall, England, in a poor family. His father, whodied when Davy was a boy, had lost money inunwise investments. So Davy worked to help hismother pay off the debts. He disliked being astudent, although he liked reading about science.

With no money for further education, Davybegan to work for a surgeon-pharmacist. He alsostarted learning about geography, languages,and philosophy on his own. Davy even dabbledin poetry. At 19, he decided to concentrate onchemistry and eventually became a major con-tributor to the field of electrochemistry, thescience involving the relation of electricity tochemical changes.

Davy discovered nitrous oxide after testing theeffects of hydrogen and carbon dioxide on him-self. (He liked to use himself as a human guineapig.) Nitrous oxide is a gas that consists ofnitrogen and oxygen. He discovered that itseffects often made him feel very happy or verysad. The feeling of happiness eventually gavenitrous oxide another name: laughing gas. Mostimportantly, Davy recognized that it could beused as an anesthetic. An anesthetic is a chemicalused to dull pain during surgery.

In 1808, Davy invented the carbon arc lamp. Hehad proposed using carbon as the electrodematerial instead of metal. (Electrodes are con-ductors used to establish electrical contact with anonmetallic part of a circuit.) With carbon elec-trodes, he made a strong electric current leapfrom one electrode to the other. This created anintense white light. Davy’s invention marked thebeginning of the era of electric light. Arc lampsare still used today.

In addition, Davy built a large battery that heused to break down substances that most scien-tists thought were pure elements. In 1807, hediscovered the element potassium by using aprocess known as electrolysis. Electrolysis is areaction in which electric current is used to bringabout chemical changes. Less than a week later,Davy also isolated the element sodium by thesame procedure. Then in 1808, he isolatedcalcium, magnesium, barium, and strontium.Davy was only 29 by the time he had discoveredall of these elements.

Davy went on to make other major discoveriesand inventions. During his lifetime, Davy wasawarded many honors and medals. He died ofa stroke in 1829.

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Calcium

suffix -ium to the word calx; -ium is the ending used for almost allmetallic elements. Using the same method, Davy was also able to producefree sodium, potassium, strontium, magnesium, and barium.

Physical PropertiesCalcium is a fairly soft metal with a shiny silver surface when first cut.The surface quickly becomes dull as calcium reacts with oxygen to forma coating of white or gray calcium oxide.

Calcium’s melting point is 1,560°F (850°C) and its boiling point is2,620°F (1,440°C). It has a density of 1.54 grams per cubic centimeter.

Chemical PropertiesCalcium is a moderately active element. It reacts readily with oxygen toform calcium oxide (CaO):

2Ca + O2 ? 2CaO

Calcium reacts with the halogens—fluorine, chlorine, bromine,iodine, and astatine. The halogens are the elements that make upGroup 17 (VIIA) of the periodic table. Calcium also reacts readily withcold water, most acids, and many non-metals, such as sulfur andphosphorus. For example, calcium reacts with sulfur:

Ca + S ? CaS

Occurrence in NatureCalcium is the fifth most common element in Earth’s crust. Its abun-dance is estimated to be about 3.64 percent. It is also the fifth mostabundant element in the human body.

Calcium does not occur as a free element in nature. It is much too activeand always exists as a compound. The most common calcium compound iscalcium carbonate (CaCO3). It occurs in the minerals aragonite, calcite,chalk, limestone, marble, and travertine, and in oyster shells and coral.

Shellfish build their shells from calcium dissolved in the water. Whenthe animals die or are eaten, the shells sink. Over many centuries, thicklayers of the shells may build up and be covered with mud, sand, orother materials. The shells are squeezed together by the heavy pressureof other materials and water above them. As they are squeezed together,the layer is converted to limestone. If the limestone is squeezed evenmore, it can change into marble or travertine.

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IsotopesFive naturally occurring stable isotopes of calcium exist: calcium-40,calcium-42, calcium-43, calcium-44, and calcium-46. Isotopes are twoor more forms of an element. Isotopes differ from each other accordingto their mass number. The number written to the right of the element’sname is the mass number. The mass number represents the number ofprotons plus neutrons in the nucleus of an atom of the element. Thenumber of protons determines the element, but the number of neutronsin the atom of any one element can vary. Each variation is an isotope.

Fourteen radioactive isotopes of calcium are also known, one ofwhich, calcium-48, exists in nature. A radioactive isotope is one thatbreaks apart and gives off some form of radiation. Radioactive isotopesare produced when very small particles are fired at atoms. These particlesstick in the atoms and make them radioactive.

Two radioactive isotopes of calcium are used in research and medi-cine. Calcium-45 is used to study how calcium behaves in many naturalprocesses. For example, it can be used to see how various types of soilbehave with different kinds of fertilizers. The calcium-45 is used as atracer in such studies. A tracer is a radioactive isotope whose presencein a system can easily be detected. The isotope is injected into the systemat some point. Inside the system, the isotope gives off radiation. Theradiation can be followed by detectors placed around the system.

Calcium can be found in oystershells. IMAGE COPYRIGHT

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