Transition steels bind come ligands in order to edge closer to digital saturation. In other words, the electrons donated through the ligands to form the bonds to the metal help that metal get to the next noble gas configuration. The doesn"t constantly get there, and also sometimes it overshoots, yet that"s a turbulent guide.

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Consider the coordination facility below. Cl3 consists of a cobalt complex ion and also three chloride counterions; castle are just there to balance the charge. We might think the that complex as being assembled native a cobalt ion and also six ammonia molecules. The six ammonia molecules every lend a lone pair to help the cobalt towards its octet. If us go backwards, and also disassemble the complex to that is components, we see that every of those ammonia molecules was neutral. There is no formal fee on any kind of of those nitrogens. If they room all neutral, but the complex has a positive charge, then wherein did the confident charge come from?


The answer has to be the cobalt ion. The cobalt has actually a 3+ fee (or "oxidation state"). Knowing that, us can number out how plenty of electrons cobalt has actually in its valence shell within the complex.

In the routine table, cobalt has nine valence electrons. However, if the overall complex has a fee of 3+, then the cobalt likewise had a fee of 3+. It has actually lost 3 electrons, so it only has actually six left. When it develops the complex, each ammonia donates a pair that electrons; that"s twelve total. The valence shell about cobalt consists of its very own d electrons plus that twelve donated through the ligands, for a full of eighteen.

We deserve to summarise in a table:

metal valence e- (or d e-)9 e-
charge top top complex3+
charge ~ above ligands0
charge ~ above metal3+
metal ion d e-6 e-
e- donated through ligands6 x 2 = 12 e-
total18 e-

Cl2 is a very similar example. This time, as soon as we dissect the complex, we discover a chlorine the would have a formal charge of 1- (we constantly assume the ligands all had octets prior to they join the metal). The overall facility has a 2- charge; taking into account the there is a charge of -1 top top the chloride within the complex, then the cobalt ion must have actually a charge of 3+ in bespeak to come at that all at once 2+ charge.


Again,we can use a table to count the electrons on cobalt in the complex.

metal valence e- (or d e-)9 e-
charge on complex2+
charge ~ above ligands1-
charge top top metal3+
metal ion d e-6 e-
e- donated by ligands12 e-
total18 e-

Problem TM3.1.

Confirm the electron count on the steel is 18 electrons in each of the complying with complexes.

a) Pd(PPh3)4 b) Cr(CO)6 c) ClO4

d) Fe(CO)5 e) K4

Problem TM3.2.

Determine the electron counting on the metal in every of the following complexes.

a) RhClH2(PPh3)2 b) (ClO4)2 c) (BF4)2 d) K2

On the next page, we will see just how some ligands deserve to bind to a metal an ext than once. The helps them hold on much more tightly.

See a an ext in-depth discussion of coordination complexes in a later on course.

This site is written and maintained by kris P. Schaller, Ph.D., university of Saint Benedict / Saint John"s university (with contribute from other authors together noted). That is freely easily accessible for education use.

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Structure & Reactivity in Organic, Biological and Inorganic Chemistry by chris Schaller is licensed under a an innovative Commons Attribution-NonCommercial 3.0 Unported License.