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Coordinate Covalent Bond: Definition & Examples

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  • 0:02 Coordinate Covalent Bond
  • 3:11 Coordination and…
  • 4:36 Deconstruct…
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Lesson Transcript
Instructor: Elizabeth (Nikki) Wyman

Nikki has a master's degree in teaching chemistry and has taught high school chemistry, biology and astronomy.

In this lesson, learn about coordinate covalent bonds and the compounds that contain them. The lesson will also offer an understanding of how to interpret formulas of coordination compounds and deduce the number of coordinate covalent bonds present.

Coordinate Covalent Bond

Some of life's most critical processes can be attributed to coordinate covalent bonds and the coordination compounds that contain them. For example, oxygen is distributed throughout our body via the heme group, an iron containing coordination compound present in blood cells.

Before diving into the world of coordination compounds and coordinate covalent bonds, let's review ionic compounds. Ionic compounds are composed of one or more cations (positive ions) and one or more anions (negative ions) that are bonded together because they are oppositely charged. The positive and negative charges balance each other so that the overall charge on the compound is zero.

Coordination compounds are just like slightly more complicated ionic compounds. In a coordination compound, one of the ions has to be a complex ion. It's usually pretty easy to identify which ion is the complex ion because it looks complex! Here are two ions that bond to form a coordination compound. Which one is the complex ion?

[Pt(NH3)3 Br]+

Cl-

If you noticed that the first ion is vastly more complicated than the simple chloride ion, nice work! Your observations have helped you correctly identify a complex ion. Try again to identify the complex ion:

3K+

[CoF6]3-

This time, the second ion shown is more complex.

A complex ion is made of two things, a metal ion and compounds called ligands. Ligands are neutral molecules or ions containing lone electron pairs that can bond with the metal ion. Common ligands are ammonia (NH3), water (H2 O) and halide ions (Cl-, Br-).

Ligands are considered Lewis bases because they are sharing their electron pairs with the metal ion. As you may recall, metal ions are always positive, so they are quite attractive to lone pairs of electrons. The resulting bond between the metal ion and the ligands are known as coordinate covalent bonds.

Coordinate covalent bond (shown in red) between the platinum metal ion and the lone pair on nitrogen in NH 3.
coordinate covalent bond

In this image, a coordinate covalent bond is shown in red between the platinum metal ion and the lone pair on nitrogen NH3. Notice that in the previous examples, both complex ions contain metal ions and several ligands. Not all of the ligands have to be the same. In the first example, [Pt(NH3)3 Br]+, there are three ammonia ligands, NH3, and one bromide ion ligand. Each ligand has formed a bond with the platinum ion for a total of four coordinate covalent bonds. In the second example [CoF6)]3-, there are six fluoride ligands, each forming coordinate covalent bonds with the cobalt ion for a total of six bonds.

As you might have observed, complex ions can be positive or negative. Like simpler ionic compounds, complex ions will bond with ions of the opposite charge called counter ions, forming a neutral compound. A complete coordination compound is written with the complex ion in brackets and the counter ions outside the brackets. There should be no charge on the compound because it is neutral.

Here are the same examples written as complete compounds:

[Pt(NH3)3 Br]Cl

K3 [CoF6]

Coordination and Oxidation Numbers

Coordination compounds exist because some metals can do some funky things with their electrons. Some elements, like the alkali metals in column one, are capable of bonding with just their outermost set of electrons, known as valence electrons, so they are limited in the number of bonds they can make. Other metals are not though. Some metals, like transition metals, are thought to have two sets of electrons that can participate in bonding, primary valence electrons, and secondary valence electrons.

Secondary valence electrons are involved in the formation of coordination covalent bonds, or bonds between the metal ion and the ligands. The number of bonds a metal is capable of making is known as the coordination number. Metals are capable of having multiple coordination numbers. Six and four are the most common coordination numbers.

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