Inaugurated by IN-SPACe
ISRO Registered Space Tutor
S7-SA5-0760
What is Coordination Number (Coordination Chemistry)?
Grade Level:
Class 12
AI/ML, Physics, Biotechnology, FinTech, EVs, Space Technology, Climate Science, Blockchain, Medicine, Engineering, Law, Economics
Definition
What is it?
In coordination chemistry, the Coordination Number (CN) tells us how many atoms or groups (called ligands) are directly attached to the central metal atom or ion. It's like counting the number of friends directly holding hands with you in a circle.
Simple Example
Quick Example
Imagine you are the central metal atom, and your friends are ligands. If 4 friends are directly holding your hands, your coordination number is 4. It doesn't matter how many other friends are standing nearby, only those directly connected count.
Worked Example
Step-by-Step
Let's find the coordination number for the complex ion [Co(NH₃)₆]³⁺.
STEP 1: Identify the central metal atom. Here, it is Cobalt (Co).
---
STEP 2: Identify the ligands. The ligands are the ammonia molecules (NH₃).
---
STEP 3: Determine how many ligands are directly attached to the central metal. The subscript '6' outside the parenthesis for NH₃ tells us there are six ammonia molecules.
---
STEP 4: Each NH₃ molecule is a monodentate ligand, meaning it binds to the central metal at one point.
---
STEP 5: Count the total number of points of attachment. Since 6 NH₃ ligands are attached, and each attaches at one point, the total is 6 x 1 = 6.
---
ANSWER: The coordination number of Co in [Co(NH₃)₆]³⁺ is 6.
Why It Matters
Understanding coordination number is vital for designing new materials and medicines. Chemists use it to predict the shape of molecules, which helps in creating better catalysts for industrial processes or developing new drugs for diseases. It's a key concept for careers in chemical engineering, pharmacology, and materials science.
Common Mistakes
MISTAKE: Counting all atoms within the ligand as part of the coordination number | CORRECTION: Only count the number of donor atoms from the ligands that are directly bonded to the central metal atom.
MISTAKE: Confusing the charge of the complex with the coordination number | CORRECTION: The coordination number is about the number of bonds, not the overall electrical charge of the complex ion.
MISTAKE: Assuming all ligands attach at only one point (monodentate) | CORRECTION: Some ligands (like ethylenediamine) are 'bidentate' and attach at two points. You must multiply the number of such ligands by 2 when counting the coordination number.
Practice Questions
Try It Yourself
QUESTION: What is the coordination number of Nickel (Ni) in [Ni(CN)₄]²⁻? (Assume CN⁻ is a monodentate ligand) | ANSWER: 4
QUESTION: Determine the coordination number of Platinum (Pt) in [Pt(en)₂]²⁺, where 'en' (ethylenediamine) is a bidentate ligand. | ANSWER: 4 (since 2 bidentate ligands each attach at 2 points, 2 x 2 = 4)
QUESTION: In the complex [Cr(H₂O)₄Cl₂]⁺, what is the coordination number of Chromium (Cr)? (Both H₂O and Cl⁻ are monodentate ligands) | ANSWER: 6 (4 from H₂O and 2 from Cl⁻, totaling 6)
MCQ
Quick Quiz
What is the coordination number of Iron (Fe) in the complex [Fe(C₂O₄)₃]³⁻, given that oxalate (C₂O₄²⁻) is a bidentate ligand?
3
4
6
9
The Correct Answer Is:
C
Each oxalate ligand (C₂O₄²⁻) is bidentate, meaning it forms two bonds with the central metal. Since there are three such ligands, the total number of bonds is 3 ligands * 2 bonds/ligand = 6.
Real World Connection
In the Real World
Coordination complexes are everywhere! The hemoglobin in our blood, which carries oxygen, is a coordination complex where an iron atom is at the center. The coordination number of iron in hemoglobin helps it bind oxygen effectively. Similarly, many dyes used in textiles or the catalysts in car exhaust systems rely on specific coordination numbers to function.
Key Vocabulary
Key Terms
LIGAND: An atom or group of atoms that donates electrons to a central metal atom to form a coordinate bond. | MONODENTATE: A ligand that binds to the central metal atom at only one point. | BIDENTATE: A ligand that binds to the central metal atom at two points. | CENTRAL METAL ATOM: The atom or ion in a coordination complex to which ligands are attached.
What's Next
What to Learn Next
Now that you understand coordination number, you're ready to explore the 'Shapes of Coordination Complexes.' Knowing the coordination number is the first step to predicting how these fascinating molecules arrange themselves in 3D space, which is super important for their functions!
