Question

In your own words, describe the following terms or symbols: (a) coordination number; (b) \(\Delta_{\mathrm{o}} ;\) (c) ammine complex; (d) enantiomer.

Short answer

Coordination number is the number of donor atoms attached to a central atom. \(\Delta_{\mathrm{o}}\) is the energy difference between t2g and eg orbitals in an octahedral complex. An ammine complex is a compound where an ammonia molecule is bonded to a metal ion. Enantiomers are molecules that are mirror images of each other yet are non-superimposable.

Step-by-step solution

Definition of Coordination Number

Coordination number in chemistry refers to the total number of donor atoms attached to the central atom in a complex or coordination compound. These donor atoms can be a part of the same molecule or different molecules.

Definition of \(\Delta_{\mathrm{o}}\)

\(\Delta_{\mathrm{o}}\) refers to the energy gap or difference in energy between the t2g and eg orbitals in an octahedral complex in the field of crystal field theory. It is often represented in terms of energy unit like joules or electronvolts.

Definition of Ammine Complex

An ammine complex is a type of coordination compound where one or more ammonia molecules are bonded to a metal ion. The ammonia acts as a ligand, a molecule or ion that forms a complex with a central atom or ion.

Definition of Enantiomer

Enantiomers are a pair of molecules that are mirror images of each other, like left and right hands. These are non-superimposable and have identical physical properties but they can interact differently with other chiral molecules or a plane of polarized light.

Key concepts

Coordination Number

The coordination number is a fundamental concept in coordination chemistry, referring to the number of ligand atoms that are directly bonded to the central atom in a coordination complex. Imagine a central metal ion as being at the center of a larger molecular structure, surrounded by various 'supporting' molecules or ions, known as ligands. The coordination number effectively tells us how many seats at the molecular table are occupied by these supporting characters.

For example, if a central iron ion is surrounded by six cyanide ions, the coordination number of iron in this complex is six. Coordination numbers are essential in determining the geometry and the physical properties of the complex. They can vary, often ranging from 2 to 12, with 4 (tetrahedral, square planar) and 6 (octahedral) being the most common in inorganic coordination complexes.

Crystal Field Theory

Crystal Field Theory (CFT) is a model that helps us understand the color and magnetism of coordination compounds. It describes the effect of the electric field produced by the surrounding ligands on the energy levels, or orbitals, of the metal ion at the center of a coordination complex.

CFT focuses on how the metal ion's d orbitals are affected by the ligands. An important term in CFT is \(\Delta_{\mathrm{o}}\), representing the energy difference between two specific sets of d orbitals, named t2g and eg, in an octahedral complex. This energy gap, indicated by \(\Delta_{\mathrm{o}}\), is critical because it influences the absorbance of light and, consequently, the color of the complex. A larger \(\Delta_{\mathrm{o}}\) means more energy is required to promote electrons between these orbitals, affecting the color you see. Understanding \(\Delta_{\mathrm{o}}\) and CFT is important in fields like materials science and biochemistry.

Ammine Complex

An ammine complex is a specific type of coordination compound where ammonia (NH3) serves as the ligand, bonding to a central metal cation. The term 'ammine' in this context refers to the presence of the ammonia molecules, not to be confused with amines, which are organic compounds.

Ammine complexes are common in coordination chemistry, with the platinum-ammine complex being a classic example studied extensively due to its relevance in chemotherapy. In an ammine complex, the nitrogen atom donates its lone pair of electrons to form a coordinate bond with the metal ion, stabilizing the overall structure. The number of ammonia ligands attached can vary, directly influencing the compound's coordination number and its properties.

Enantiomer

Enantiomers are a pair of stereochemically related molecules that are mirror images of each other yet cannot be superimposed on one another. This concept is akin to the relationship between left and right hands – they look the same but are oriented differently. Enantiomers are characterized by their chiral nature; that is, they have a handedness due to the presence of an asymmetric carbon atom with four distinct substituents, leading to non-superimposable mirror images.

Although enantiomers have identical physical properties, such as boiling points and densities, they often display different chemical behaviors, especially when interacting with other chiral compounds, including biological systems. One of the key ways enantiomers differ in their properties is in the way they rotate plane-polarized light, one in the clockwise direction (dextrorotatory) and the other in the counterclockwise direction (levorotatory), an attribute that is essential in analyzing their behavior in various scientific fields like pharmacology.