chemistry

Ligand bond number

Ligand bond number is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Ligand bond number rather than just read about it. In short: Ligand bond number (LBN) represents the effective total number of ligands or ligand attachment points surrounding a metal center, labeled M. More simply, it represents the number of coordination sites occupied on the metal.

Key takeaways

Ligand bond number belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ligand bond number to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ligand bond number from memory before moving on to harder problems.

Reference excerpt

Ligand bond number (LBN) represents the effective total number of ligands or ligand attachment points surrounding a metal center, labeled M. More simply, it represents the number of coordination sites occupied on the metal. Based on the covalent bond classification method (from where LBN is derived), the equation for determining ligand bond number is as follows:

LBN = L + X + Z Where L represents the number of neutral ligands adding two electrons to the metal center (typically lone electron pairs, pi-bonds and sigma bonds. Most encountered ligands will fall under this category. X represents covalent-bonding ligands such as halogen anions. Z represents, though rarely encountered electron accepting ligands or dative bond forming ligands. The ligand bond number convention is most commonly encountered within inorganic chemistry and it's related fields organometallic chemistry and bioinorganic chemistry.

Comparisons with Coordination Number

On comparison to the classical coordination numbers, some major differences can be seen. For example, (η5–cyclopentadienyl)2Cr (ML4X2) and (η6–benzene)2Cr (ML6) both have a LBN of 6 as compared to classical coordination numbers of 10 and 12. Well known complexes such as Ferrocene and Uranocene also serve as examples where LBN and coordination number differ. Ferrocene has two η5 cyclopentadienyl ligands while Uranocene has two η8 cyclooctatetraene ligands; however, by covalent bond classification the complexes are found to be ML4X2 and ML6X4. This corresponds to LBN values of 6 and 10 respectively, even though the total coordination numbers would be 10 and 16. The usefulness of LBN to describe bonding extends beyond just sandwich compounds. Co(CO)3(NO) is a stable 18-electron complex in part due to the bonding of the NO ligand in its linear form. The donation of the lone pair on the nitrogen makes this complex ML4X, containing 18 electrons. The traditional coordination number here would be 4, while the CBC more accurately describes the bonding with a LBN of 5. In simple cases, the LBN is often equal to the classical coordination number (ex. Fe(CO)5, etc.)

Ligand bond plots

The LBN for transition metals trends downward from left to right across the periodic table. This trend is highlighted in the LBN plots of Groups 3 through 10. Groups exhibit trends, but the LBN for individual complexes can vary.

References

Illustrations

Worked examples

Example 1 — a first encounter with Ligand bond number

Start with the simplest possible case. Write down what Ligand bond number claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Ligand bond number before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Ligand bond number ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Ligand bond number

In research: Ligand bond number appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Ligand bond number in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Ligand bond number is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical bonding, so understanding it makes those chapters shorter.
In everyday life: Look for Ligand bond number outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Ligand bond number” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Ligand bond number in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ligand bond number means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Ligand bond number out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ligand bond number in simple terms?

Why does Ligand bond number matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Ligand bond number?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Ligand bond number.