| Calcium is an alkaline earth metal. The alkaline | | | | Calcium reacts with the halogens— fluorine, |
| earth metals include beryllium, magnesium, | | | | chlorine, bromine, iodine, and astatine. Calcium also |
| strontium, barium, and radium. The alkaline earth | | | | reacts readily with cold water, most acids, and |
| metals are more chemically active than most | | | | most nonmetals, such as sulfur and phosphorus. |
| metals. Only the alkali metals in Group I (IA) are | | | | Calcium is the fifth most common element in the |
| more reactive. Calcium compounds are common | | | | Earth's crust. Its abundance is estimated to be |
| and abundant in the Earth's crust. Humans have | | | | about 3.64 percent. It is also the fifth most |
| used calcium compounds for hundreds of years in | | | | abundant element in the human body. Calcium |
| construction, sculpture, and roads. Calcium metal | | | | does not occur as a free element in nature. It is |
| was not prepared in a pure form until 1808 when | | | | much too active and always exists as a |
| English chemist Humphry Davy (1778-1829) | | | | compound. The most common calcium compound |
| passed an electric current through molten | | | | is calcium carbonate (CaCO3). It occurs as |
| (melted) calcium chloride. Metallic calcium has | | | | aragonite, calcite, chalk, limestone, marble, and |
| relatively few uses. However, calcium compounds | | | | travertine, and in oyster shells and coral. Shellfish |
| are well known and widely used. They include | | | | build their shells from calcium dissolved in the |
| chalk, gypsum, limestone, marble, and plaster of | | | | water. When the animals die or are eaten, the |
| paris. | | | | shells sink. Over many centuries, thick layers of |
| It is impossible to say when humans first knew | | | | the shells may build up and be covered with mud, |
| about or used compounds of calcium. Whenever | | | | sand, or other materials. The shells are squeezed |
| they used limestone to build a structure, they | | | | together by the heavy pressure of other |
| were using a compound of calcium. Limestone is | | | | materials and water above them. As they are |
| the common name for calcium carbonate | | | | squeezed together, the layer is converted to |
| (CaCO3). Whenever humans built a statue or | | | | limestone. If the limestone is squeezed even |
| monument out of marble, they were using | | | | more, it can change into marble or travertine. |
| calcium carbonate in another form. Ancient | | | | Calcium carbonate can be found in coral. |
| Egyptians and early Greeks used mortar, a | | | | Six naturally occurring isotopes of calcium: |
| cement-like material that holds stones and bricks | | | | calcium-40, calcium-42, calcium-43, calcium-44, |
| together. Early mortar was made by roasting or | | | | calcium-46, and calcium-48exist. Radioactive |
| heating limestone for long periods of time. Water | | | | isotopes of calcium have also been made. Two |
| was then mixed with the powder, which would | | | | radioactive isotopes of calcium are used in |
| then dry to form a strong bond. | | | | research and medicine. Calcium-45 is used to |
| Humphry Davy (1788-1829) was a major | | | | study how calcium behaves in many natural |
| contributor to the field of electrochemistry. He is | | | | processes. For example, it can be used to see |
| best known for discovering calcium, sodium, | | | | how various types of soil behave with different |
| potassium, magnesium, strontium, and barium. He | | | | kinds of fertilizers. The calcium-45 is used as a |
| also discovered nitrous oxide and two types of | | | | tracer in such studies. A tracer is a radioactive |
| lamps. Davy grew up in Cornwall, England, in a | | | | isotope whose presence in a system can easily |
| poor family. His father, who died when Davy was | | | | be detected. The isotope is injected into the |
| a boy, had lost money in unwise investments, so | | | | system at some point. Inside the system, the |
| Davy helped his mother pay off the debts. He | | | | isotope gives off radiation. That radiation can be |
| disliked being a student, though he liked reading | | | | followed by detectors placed around the system. |
| about science. In later life, he said he was happy | | | | Calcium-45 can also be used as a tracer in the |
| he did not study too hard because he had more | | | | study of glassy materials, detergents, and water |
| time to think on his own. | | | | purification systems. |
| With no money for further education, the | | | | Both calcium-45 and calcium-47 can be used to |
| 17-year-old Davy began to work for a | | | | study how calcium is used in the body. A doctor |
| surgeon-pharmacist. He also started learning on his | | | | may think that a person's body is not using |
| own about other subjects that interested him, | | | | calcium properly in making bones or regulating |
| such as geography, languages, and philosophy. He | | | | nerve messages. The doctor can use calcium-45 |
| even wrote poems that later earned him the | | | | or calcium-47 to find out more about this problem. |
| respect and friendship of William Wordsworth, | | | | The radioactive isotope is injected into the |
| Samuel Coleridge, and other leading English poets | | | | person's bloodstream. Then its path can be |
| of his time! At 19, Davy read a chemistry book | | | | followed by the radiation it gives off. The doctor |
| by the famous French scientist Antoine-Laurent | | | | can then tell if the calcium is being used normally |
| Lavoisier (1743-94). That book convinced him to | | | | in the body. Pure calcium metal can be made by |
| concentrate on chemistry. For the rest of his life, | | | | the same method used by Davy. An electric |
| Davy's career was marked by brilliant scientific | | | | current is passed through molten calcium chloride. |
| explorations in chemistry and electrochemistry. | | | | There is not much demand for pure calcium. Most |
| Davy discovered nitrous oxide after testing the | | | | calcium is used in the form of limestone, gypsum, |
| effects of hydrogen and carbon dioxide on him. | | | | or other minerals that can be mined directly from |
| (He liked to use himself as a human guinea pig!) | | | | the earth. Shellfish build their shells from calcium |
| Nitrous oxide is a gas consisting of nitrogen and | | | | dissolved in the water. |
| oxygen. While studying nitrous oxide gas, he | | | | Calcium metal has relatively few uses. It is |
| discovered that its effects often made him feel | | | | sometimes used as a "getter." A getter is a |
| very happy or very sad. The feeling of happiness | | | | substance that removes unwanted chemicals |
| eventually gave nitrous oxide another name: | | | | from a system. Calcium is used as a getter in the |
| laughing gas. Most importantly, though, Davy | | | | manufacture of evacuated glass bulbs. Calcium is |
| recognized that it could be used as an anesthetic, | | | | added to the bulb while it is being made. It then |
| a chemical used to dull pain during minor surgery. | | | | combines with gases left in the glass in the final |
| In 1808, Davy invented the carbon arc lamp. He | | | | stages of manufacture. Calcium is also used as a |
| had proposed using carbon as the electrode | | | | getter in the production of certain metals, such as |
| material instead of metal. With carbon electrodes, | | | | copper and steel. The calcium removes unwanted |
| he made a strong electric current leap from one | | | | elements that would otherwise contaminate the |
| electrode to the other. This created an intense | | | | metal. Calcium is also used to make alloys. An |
| white light. Davy's invention marked the beginning | | | | alloy of calcium and cerium is used in flints found |
| of the era of electric light. Arc lamps are still used | | | | in lighters (the elements that create sparks). |
| today. | | | | The starting point for the manufacture of most |
| Using his knowledge of electricity, Davy built a | | | | calcium compounds is limestone. Limestone occurs |
| large battery which he used to break down | | | | naturally in large amounts in many parts of the |
| substances most scientists thought were pure | | | | world. It is usually mined from open-pit quarries. A |
| elements. In 1807, he discovered the element | | | | quarry is a large hole in the ground from which |
| potassium. He created this by using electrolysis. | | | | useful minerals are taken. Limestone is first |
| Within a week he isolated sodium in a similar way. | | | | heated to obtain lime, or calcium oxide (CaO). |
| Then in 1808, he used a slightly modified method | | | | Lime is one of the most important chemicals in |
| to isolate calcium, magnesium, barium, and | | | | the world. It usually ranks in the top five |
| strontium. Davy was only 29 by the time he had | | | | chemicals produced in the United States. In 1996, |
| discovered all of these elements. Davy later | | | | about 19 billion kilograms (42 billion pounds or 21 |
| invented the miner's lamp (now known as the | | | | million tons) of lime was produced in the United |
| Davy lamp). He learned that methane was the | | | | States. |
| mine gas that caused explosions. But he realized it | | | | Lime is used in the production of metals. It is used |
| ignited only at high temperatures. So he designed | | | | during the manufacture of steel to remove |
| a lamp in which the flame was surrounded by | | | | unwanted sand, or silicon dioxide (SiO2), present in |
| wire gauze. This reduced the heat and prevented | | | | iron ore. The product formed in this reaction, |
| flammable gases from igniting which made | | | | calcium silicate (CaSiO3), is called slag. Another |
| coal-mining safer by reducing the number of | | | | important use of lime is in pollution control. Many |
| explosions in mines. Davy was rewarded by many | | | | factories release harmful gases into the |
| honors and medals for his discoveries and | | | | atmosphere through smokestacks. Lining a |
| inventions. He died of a stroke in 1829 at the age | | | | smokestack with lime allows some of these |
| of 49. | | | | gases to be captured. The lime is known as a |
| An important calcium compound used by early | | | | scrubber. Lime captures one harmful gas, sulfur |
| civilizations was plaster of paris. Plaster of paris is | | | | dioxide (SO2), which is a contributor to acid rain (a |
| made by heating gypsum, or calcium sulfate | | | | form of precipitation that is significantly more |
| (CaSO4), to remove the water that makes it | | | | acidic than neutral water, often produced as the |
| crystallize. Water was added and it hardened into | | | | result of industrial processes). Calcium sulfite |
| a brittle, cement-like substance. Until recently, it | | | | (CaSO3) is a solid that can be removed from the |
| was most often used to make casts to protect | | | | inside of the smokestack. |
| broken bones. However, it has largely been | | | | At one time, lime was used as a source of light in |
| replaced by fiberglass, which is lighter, yet | | | | theaters. When lime is heated to a high |
| stronger. The first mention of plaster of paris to | | | | temperature, it gives off an intense white light. |
| protect broken bones can be found in a book | | | | Pots of hot lime were often used to line the front |
| written by Persian pharmacist Abu Mansur | | | | of the stage. The light the pots gave off helped |
| Muwaffaw in about 975 A.D. | | | | the audience see the performers. As a result, the |
| By the 1700s, chemists had learned a great deal | | | | performers were said to be "in the limelight." That |
| about calcium compounds. They knew that | | | | phrase is still in use today, but lime is no longer |
| limestone; gypsum, marble, and many other | | | | used as a source of light in theaters. Lime is also |
| commonly occurring compounds all contain a | | | | used in water purification and waste treatment |
| common element. They called the element calx. | | | | plants. When water combines with water, it forms |
| That word comes from the Latin term for lime. | | | | slaked lime, or calcium hydroxide (Ca(OH)2). |
| In 1807, Davy isolated the new element. Davy | | | | Slaked lime traps impurities present in the water |
| invented a system for melting compounds of | | | | as it forms. It carries the impurities with it as it |
| elements that were difficult to separate by usual | | | | sinks to the bottom of the tank. |
| methods. He passed an electric current through | | | | Lime is used to make more than 150 different |
| the compound, causing the compounds to break | | | | industrial chemicals. Milk is a good source of |
| into parts. One of those parts was calx. He | | | | calcium. Calcium is essential to both plant and |
| created the name calcium by adding the suffix | | | | animal life. In humans, it makes up about two |
| -ium to calx; -ium is the ending used for almost all | | | | percent of body weight. About 99 percent of the |
| metallic elements. Davy was also able to produce | | | | calcium in a person's body is found in bones and |
| free sodium, potassium, strontium, magnesium, | | | | teeth. Milk is a good source of calcium. The body |
| and barium. | | | | uses calcium in a compound known as |
| Calcium is a fairly soft metal with a shiny silver | | | | hydroxyapatite (Ca10(PO4)6(OH)2) to make |
| surface when first cut. The surface quickly | | | | bones and teeth hard and resistant to wear. |
| becomes dull as calcium reacts with oxygen to | | | | Calcium has many other important functions in |
| form a coating of white or gray calcium oxide. | | | | the human body. For example, it helps control the |
| Calcium's melting point is 850°C (1,560°F) and | | | | way the heart beats. An excess (too much) or |
| boiling point is 1,440°C (2,620°F). It has a | | | | deficiency (not enough) of calcium can change the |
| density of 1.54 grams per cubic centimeter. | | | | rhythm of the heart and cause serious problems. |
| Calcium is a moderately active element. It reacts | | | | Calcium also controls the function of other |
| readily with oxygen to form calcium oxide (CaO). | | | | muscles and nerves. |