Chelate

A chelate is a type of coordination compound in which a single metallic ion is attached by coordinate covalent bonds to a molecule or an ion called a ligand. The term chelate comes from the Greek word chela, meaning “crab’s claw.” The term clearly describes the appearance of many kinds of chelates, in which the ligand surrounds the central atom in a way that can be compared to the grasping of food by a crab’s claw.

Bonding in a chelate occurs because the ligand has at least two pairs of unshared electrons. These are regions of negative electrical charge to which cations such as the copper(I) and copper(II), silver, nickel, platinum, and aluminum ions are attracted. A ligand with only two pairs of unshared electrons is known as a bidentate (“two-toothed”) ligand; one with three pairs of unshared electrons, a tridentate (“three-toothed”) ligand, and so on.

The geometric shape of a chelate depends on the number of ligands involved. Those with bidentate ligands form linear molecules; those with four ligands form planar or tetrahedral molecules; and those with six ligands form octahedral molecules.

One of the most familiar examples of a chelate is hemoglobin, the molecule that transports oxygen through the blood. The “working part” of a hemoglobin molecule is heme, a complex molecule at whose core is an iron(II) ion bonded to four nitrogenatoms with coordinate covalent bonds.

Among the most common applications of chelates is in water softening and treatment of poisoning. In the former instance, a compound such as sodium tripolyphosphate is added to water. That compound forms chelates with calcium and magnesium ions, those responsible for the hardness in water. Because of their ability to “tie up” metal ions in chelates, compounds like sodium tripolyphosphate are sometimes referred to as sequestering agents.

A typical sequestering agent used to treat poison victims is ethylenediaminetetraacetic acid, commonly known as EDTA. Suppose that a person has swallowed a significant amount of lead and begins to display the symptoms of lead poisoning. Giving the person EDTA allows that molecule to form chelates with lead ions, removing that toxic material from the bloodstream.

Chelate

A chelate is a type of coordination compound in which a single metallic ion is attached by coordinate covalent bonds to a molecule or an ion called a ligand . The term chelate comes from the Greek word chela, meaning "crab's claw." The term clearly describes the appearance of many kinds of chelates, in which the ligand surrounds the central atom in a way that can be compared to the grasping of food by a crab's claw.

Bonding in a chelate occurs because the ligand has at least two pairs of unshared electrons. These unshared pairs of electrons are regions of negative electrical charge to which are attracted cations such as the copper(I) and copper(II), silver, nickel, platinum, and aluminum ions. A ligand with only two pairs of unshared electrons is known as a bidentate ("two-toothed") ligand; one with three pairs of unshared electrons, a tridentate ("three-toothed") ligand, and so on.

The geometric shape of a chelate depends on the number of ligands involved. Those with bidentate ligands form linear molecules, those with four ligands form planar or tetrahedral molecules, and those with six ligands form octahedral molecules.

One of the most familiar examples of a chelate is hemoglobin, the molecule that transports oxygen through the blood . The "working part" of a hemoglobin molecule is heme, a complex molecule at whose core is an iron(II) ion bonded to four nitrogen atoms with coordinate covalent bonds.

Among the most common applications of chelates is in water softening and treatment of poisoning. In the former instance, a compound such as sodium tripolyphosphate is added to water. That compound forms chelates with calcium and magnesium ions, ions responsible for the hardness in water. Because of their ability to "tie up" metal ions in chelates, compounds like sodium tripolyphosphate are sometimes referred to as sequestering agents.

A typical sequestering agent used to treat poison victims is ethylenediaminetetraacetic acid, commonly known as EDTA. Suppose that a person has swallowed a significant amount of lead and begins to display the symptoms of lead poisoning. Giving the person EDTA allows that molecule to form chelates with lead ions, removing that toxic material from the bloodstream.

Chelate

A chemical compound in which one atom is enclosed within a larger cluster of atoms that surrounds it like an envelope. The term comes from the Greek word chela, meaning claw. Chelating agents—compounds that can form chelates with other atoms—have a wide variety of environmental applications. For example, the compound ethylenediaminetetraacetic acid (EDTA) is used to remove lead from the blood. EDTA molecules surround and bind to lead atoms, and the chelate is then excreted in the urine. EDTA can also be used to soften hard water by chelating the calcium and magnesium ions that cause hardness.

che·late / ˈkēˌlāt/ • n. Chem. a compound containing a ligand (typically organic) bonded to a central metal atom at two or more points.• adj. Zool. (of an appendage) bearing chelae.• v. [tr.] Chem. form a chelate with.DERIVATIVES: che·la·tion / kēˈlāshən/ n.che·la·tor / -ˌlātər/ n.

chelate
1. (adj.) Pincer-like or claw-like.

2. (noun) A ring structure formed as a result of the reaction of a metal ion with two or more groups on a ligand. Haemoglobin and chlorophyll are chelate compounds in which the metal ions are iron and magnesium respectively.