Problem 80 - Chemistry The Molecular Science

Question

An aqueous solution of \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}\) is purple. Predict the approximate wavelength and predominant color of light absorbed by the complex.

Step-by-Step Solution

Answer

The complex likely absorbs light around 500-560 nm, corresponding to yellow-green.

Step 1: Identify the observed color

The complex \([\mathrm{Ni}(\mathrm{NH}_{3})_{6}]^{2+}\)is described as being purple in color.

Step 2: Recognize complementary colors

In color theory, the observed color of a substance is approximately the complementary color of the light it absorbs. Using a color wheel, we determine that the complementary color of purple is yellow-green.

Step 3: Estimate the absorbed wavelength range

The absorbed wavelengths correspond to visible light in the yellow-green region, which typically ranges from approximately 500 nm to 560 nm.

Step 4: Make predictions

Based on the color theory and the complementary colors, the complex likely absorbs light in the region of yellow-green wavelengths, around 500-560 nm.

Key Concepts

Color Theory

Color theory is an essential concept when studying the behavior of light and color in chemistry, especially with coordination compounds. It provides a way to understand how complex ions absorb and emit light. Color theory relies on the idea that the colors we see are related to the wavelengths of light reflected or transmitted by a substance.

• When a material absorbs certain wavelengths, the color we perceive is the combination of the remaining wavelengths that are not absorbed.
• This explains why a substance might exhibit a specific color even if the light of that color is not what is being absorbed.

Color perception is, therefore, linked to the absorption and reflection of light, which can be predicted and understood using the principles outlined by color theory.

Complementary Colors

Complementary colors play a significant role in understanding the colors of coordination compounds. These are colors located opposite each other on the color wheel. When one wavelength is absorbed, its complementary color is observed.

• For example, when a complex solution is purple, it absorbs light from the yellow-green region, which lies opposite purple on the color wheel.
• This balance helps determine the appearance of colors for various chemicals, a fundamental aspect of identifying the specific properties of a complex substance.

By using this concept, chemists can predict the colors of compounds and understand the relationship between the absorbed and observed colors in a sample.

Wavelength Absorption

Wavelength absorption is crucial to understanding how compounds like transition metal complexes appear colored. It refers to the specific wavelength range that a complex absorbs, affecting its color impression to the human eye.

• The visible spectrum of light covers from about 400 nm to 700 nm. Each color corresponds to a particular part of this range.
• When a complex absorbs light within a specific wavelength, the complementary color is what we perceive.

In coordination chemistry, the ligand and metal center influence the specific wavelengths that are absorbed, providing insight into the electronic transitions occurring within the compound.

Transition Metal Complexes

Transition metal complexes often exhibit vibrant colors due to their ability to absorb visible light. This happens because of the d-d electronic transitions enabled by their partially filled d orbitals.

• These complexes are formed when central metal atoms bond with surrounding ligands, creating specific geometries and electronic environments.
• The interactions between the metal ions and ligands can result in different energy gaps, influencing which wavelengths are absorbed.

The color that we observe in these complexes is a direct result of these interactions causing certain wavelengths of light to be absorbed, with the remaining light contributing to the observed color. Transition metal complexes serve as excellent models for studying light absorption and emission in chemistry.