Complex ions are fascinating chemical structures where molecules or ions... Show more
Chemistry54 views·Updated May 15, 2026·4 pagesExploring Complex Ion Shapes: Chapter 24.2
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Complex Ion Formation
Ever wondered how metal ions can hold onto other molecules so tightly? Complex ions form when one or more molecules or negative ions bond directly to a central metal ion. The molecules or ions that attach are called ligands, and they're basically electron donors.
What makes this bonding special is that ligands donate a pair of electrons to the metal ion, creating what's called a coordinate bond (also known as a dative covalent bond). Think of it like the ligand is lending its electrons to the metal.
The overall charge of a complex ion can be positive, negative, or even neutral - it all depends on the charges of the metal ion and ligands involved.
Quick Tip: Remember that ligands are always the electron donors, whilst the metal ion is the electron acceptor!
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Coordination Numbers and Examples
The coordination number tells you exactly how many coordinate bonds are attached to the central metal ion. This number is absolutely crucial because it determines the shape of the entire complex.
The most common coordination numbers you'll encounter are 4 and 6. For example, in copper sulfate, you get [Cu(H₂O)₆]²⁺ - here the coordination number is 6 because six water molecules surround the copper ion.
In this example, water (H₂O) acts as the ligand, donating electron pairs from its oxygen atoms to form coordinate bonds with the central Cu²⁺ ion.
Exam Focus: Always identify the ligand, central metal ion, and coordination number when analysing complex ion formulas!
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Types of Ligands
Not all ligands are created equal! Monodentate ligands can only donate one pair of electrons to the central metal atom, forming just one coordinate bond. Water and ammonia are classic examples.
Bidentate ligands are more generous - they donate two pairs of electrons, forming two coordinate bonds with the same metal ion. This creates a sort of "pincer" effect around the metal.
Understanding whether a ligand is monodentate or bidentate helps predict how many ligand molecules will surround the central metal ion and what the final complex will look like.
Memory Aid: "Mono" means one, "bi" means two - think of the number of electron pairs donated!
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Complex Ion Shapes
When coordination number is 4, you'll see two possible shapes. Tetrahedral complexes have bond angles of 109.5°, like in [CuCl₄]²⁻ where four chloride ions arrange themselves around copper in a pyramid-like structure.
Square planar complexes also have coordination number 4, but the ligands arrange in a flat square with 90° bond angles. A perfect example is [Pt(NH₃)₄]²⁺, where four ammonia molecules surround platinum in one plane.
The difference between tetrahedral and square planar often depends on the specific metal ion and its electron configuration. Platinum commonly forms square planar complexes, which is why cis-platin (a cancer treatment drug) has its distinctive flat structure.
Shape Recognition: Tetrahedral = 3D pyramid, Square planar = flat square - knowing this helps predict complex properties!
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Chemistry54 views·Updated May 15, 2026·4 pagesExploring Complex Ion Shapes: Chapter 24.2
Complex ions are fascinating chemical structures where molecules or ions surround a central metal ion, creating unique shapes and properties. Understanding how these complexes form and their different geometries is crucial for A-level chemistry success.
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Complex Ion Formation
Ever wondered how metal ions can hold onto other molecules so tightly? Complex ions form when one or more molecules or negative ions bond directly to a central metal ion. The molecules or ions that attach are called ligands, and they're basically electron donors.
What makes this bonding special is that ligands donate a pair of electrons to the metal ion, creating what's called a coordinate bond (also known as a dative covalent bond). Think of it like the ligand is lending its electrons to the metal.
The overall charge of a complex ion can be positive, negative, or even neutral - it all depends on the charges of the metal ion and ligands involved.
Quick Tip: Remember that ligands are always the electron donors, whilst the metal ion is the electron acceptor!
2
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Coordination Numbers and Examples
The coordination number tells you exactly how many coordinate bonds are attached to the central metal ion. This number is absolutely crucial because it determines the shape of the entire complex.
The most common coordination numbers you'll encounter are 4 and 6. For example, in copper sulfate, you get [Cu(H₂O)₆]²⁺ - here the coordination number is 6 because six water molecules surround the copper ion.
In this example, water (H₂O) acts as the ligand, donating electron pairs from its oxygen atoms to form coordinate bonds with the central Cu²⁺ ion.
Exam Focus: Always identify the ligand, central metal ion, and coordination number when analysing complex ion formulas!
3
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Types of Ligands
Not all ligands are created equal! Monodentate ligands can only donate one pair of electrons to the central metal atom, forming just one coordinate bond. Water and ammonia are classic examples.
Bidentate ligands are more generous - they donate two pairs of electrons, forming two coordinate bonds with the same metal ion. This creates a sort of "pincer" effect around the metal.
Understanding whether a ligand is monodentate or bidentate helps predict how many ligand molecules will surround the central metal ion and what the final complex will look like.
Memory Aid: "Mono" means one, "bi" means two - think of the number of electron pairs donated!
4
of 4Sign up to see the content. It's free!
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Complex Ion Shapes
When coordination number is 4, you'll see two possible shapes. Tetrahedral complexes have bond angles of 109.5°, like in [CuCl₄]²⁻ where four chloride ions arrange themselves around copper in a pyramid-like structure.
Square planar complexes also have coordination number 4, but the ligands arrange in a flat square with 90° bond angles. A perfect example is [Pt(NH₃)₄]²⁺, where four ammonia molecules surround platinum in one plane.
The difference between tetrahedral and square planar often depends on the specific metal ion and its electron configuration. Platinum commonly forms square planar complexes, which is why cis-platin (a cancer treatment drug) has its distinctive flat structure.
Shape Recognition: Tetrahedral = 3D pyramid, Square planar = flat square - knowing this helps predict complex properties!
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