We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.
Home

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

What is Coordination Number?

By Angie Bates
Updated: Jan 28, 2024
Views: 9,417
Share

Defined by Alfred Werner in 1893, a coordination number is a term used in chemistry to denote the number of bonds a central metal ion has in a coordination compound. Coordination numbers range from two to 16, with four and six being the most common. Though they are normally used for transition metal atoms in a compound, they can also refer to nonmetallic substances as well.

Neutral atoms — which are atoms that have no charge — or cations — atoms with a positive charge — can both be the central atom in a coordination compound. These atoms are usually transition metals, which are those elements that react with halogens. Iron, copper, gold, and chromium are all examples of transition metals.

Transition metals are listed in groups three through 12 on the Periodic Table of Elements. Their reaction with other substances is usually obvious because solutions and compounds undergo a color change. For example, Ferric Chloride (FeCl) is usually green-black, but when dissolved in a solution it turns yellow. Conversely, halogens include fluorine, chlorine, and iodine. They always have seven valence electrons, or electrons capable of sharing in bonds with other atoms.

Attached to the metal ion is a ligand. Either an atom or a molecule, a ligand can be neutral or negatively charged, an anion. Ligands are usually halogens.

It is the attachments of ligands to the main metal ion that results in the coordination number. For example, Ag[NH3]2+, or diamminesilver ion, is a simple coordination compound with a coordination number of two. Ag, or silver, is the central metal ion. Attached to the silver atom are two ammonia molecules, NH3, one on either side of the atom. The plus sign in the chemical name shows that the compound is positively charged.

Coordination compounds are often used as catalysts, or substances that start or change the rate of a chemical reaction. The actual compound can be positively charged, negatively charged, or neutral. Compounds with coordination numbers may be referred to by the actual number or by a geometric name which reflects both the coordination number and the basic shape of the compound.

For example, a compound with a coordination number of two will be linear, so these compounds are called collinear. Collinear compounds are uncommon in metals, but relatively common for non-metals. Coordination numbers of three are called trigonal planar. These are rare, but are found when ligands are particularly large. Tetrahedral compounds have coordination numbers of four, while fives are either trigonal-bipyramidal or square-pyramidal.

Share
WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.

Editors' Picks

Discussion Comments
Share
https://www.wise-geek.com/what-is-coordination-number.htm
Copy this link
WiseGeek, in your inbox

Our latest articles, guides, and more, delivered daily.

WiseGeek, in your inbox

Our latest articles, guides, and more, delivered daily.