Calcium chloride is a substance frequently encountered in daily life. It serves various purposes, from acting as a de-icing agent on roads to being an additive in food products. Understanding what calcium chloride is involves exploring its fundamental building blocks and how they are arranged.
The Essential Elements
Calcium chloride is composed of two elements: calcium and chlorine. Calcium (Ca) is an alkaline earth metal, positioned in Group 2 of the periodic table. A calcium atom contains 20 protons and 20 electrons. Its outermost shell holds two electrons, which it tends to lose to achieve a stable electron configuration, forming a positively charged ion.
Chlorine (Cl) is a halogen, found in Group 17 of the periodic table. A chlorine atom contains 17 protons and 17 electrons. With seven electrons in its outermost shell, chlorine has a tendency to gain one electron to complete its outer shell and attain stability, forming negatively charged ions.
The Chemical Bond
The connection between calcium and chlorine atoms to form calcium chloride involves an ionic bond. This bond forms when electrons are transferred between atoms, leading to the creation of oppositely charged ions that are then held together by strong electrostatic forces. In the case of calcium chloride, a single calcium atom donates its two valence electrons. These are accepted by two chlorine atoms, with each gaining one electron.
This electron transfer results in the formation of a calcium ion with a positive two charge (Ca²⁺) and two chloride ions, each with a negative one charge (Cl⁻). The chemical formula CaCl₂ shows that one calcium ion combines with two chloride ions to achieve electrical neutrality. The strong attraction between the positively charged calcium ion and the negatively charged chloride ions creates a stable crystalline structure.
Natural Occurrence and Production
Calcium chloride is found naturally in various environments, often dissolved in brines or as a minor component in minerals. Significant natural sources include salt lakes and underground brine deposits, where it exists alongside other dissolved salts. The calcium component can originate from the dissolution of calcium-containing rocks like limestone.
Industrially, calcium chloride is produced as a byproduct of other chemical processes. A common method is its creation during the Solvay process, used to manufacture sodium carbonate, where it forms as a coproduct from the reaction of calcium carbonate with ammonium chloride. It can also be synthesized by reacting calcium carbonate, such as limestone, with hydrochloric acid. It can also be produced by reacting calcium hydroxide with hydrochloric acid, yielding calcium chloride and water.
How Composition Influences Properties
The ionic composition of calcium chloride directly influences its physical and chemical properties. The strong electrostatic forces within its ionic bonds require a significant amount of energy to break, contributing to its high melting point of 772 degrees Celsius (1422 degrees Fahrenheit). This strong bonding also explains why calcium chloride exists as a solid at room temperature.
Calcium chloride exhibits high solubility in water because the polar water molecules can surround and separate the charged calcium and chloride ions. This interaction leads to the dissolution of the solid compound into its constituent ions. Its ionic nature also makes it highly hygroscopic, meaning it absorbs moisture from the air. If enough moisture is absorbed, calcium chloride can dissolve in the absorbed water, a property known as deliquescence. This is due to the strong affinity of its ions for water molecules.