Question

The colors in the copper-containing minerals malachite (green) and azurite (blue) come from a single \(d\) - \(d\) transition in each compound. (a) What is the electron configuration of the copper ion in these minerals? (b) Based on their colors in which compound would you predict the crystal field splitting \(\Delta\) is larger?

Short answer

The electron configuration of the copper (II) ion in both malachite and azurite is [Ar] 3d9. Based on the colors of the minerals, which are related to the energy of the d-d transitions, the crystal field splitting energy (Δ) is larger in azurite than in malachite.

Step-by-step solution

Electron Configuration for Copper (II) Ion

The electron configuration of copper (II) ion in both malachite and azurite is [Ar] 3d9. #Step 2: Relationship between color and energy# The color of a compound is related to the absorption of light by its electrons. When the light is absorbed, electrons are promoted from their ground state to a higher energy state. The energy difference between the ground state and the excited state corresponds to the energy of the absorbed light. From the given information, the observed colors in malachite and azurite come from a single d-d transition in each compound. This means that the color we observe is the result of the absorption of light that matches the energy difference between two d-orbitals. Note that the complementary color of the absorbed light is the color we observe. Using a color-wheel, we can determine the complementary colors of the minerals. The complementary color of green is red, and the complementary color of blue is yellow.

Relationship between color and energy

The red light has a lower energy than the yellow light. Therefore, the green color (which is complementary to red) in malachite is due to a lower energy d-d transition compared to the blue color in azurite (which is complementary to yellow). #Step 3: Predict the crystal field splitting energy# Since the energy difference between the ground and excited state corresponds to the crystal field splitting energy (Δ), we can now make a prediction. Recall that the green color in malachite corresponds to a lower energy d-d transition compared to the blue color in azurite. A lower energy d-d transition means that the crystal field splitting energy is smaller in malachite compared to azurite.

Prediction of Crystal Field Splitting Energy

Based on the colors of the minerals, the crystal field splitting energy (Δ) is larger in azurite than in malachite. To summarize, the electron configuration of the copper ion in both malachite and azurite is [Ar] 3d9. Since the green color in malachite corresponds to a lower energy d-d transition compared to the blue color in azurite, we can infer that the crystal field splitting energy is larger in azurite compared to malachite.

Key concepts

Copper Ion

Copper ions play a significant role in determining the properties of minerals such as malachite and azurite. These ions can exist in various oxidation states, but in the case of these minerals, the copper is in the +2 oxidation state. This means we refer to it as the copper(II) ion. The electronic configuration of the copper(II) ion is important because it explains both the chemical and physical properties of the minerals.

For a copper(II) ion, the electron configuration is based off copper's neutral atomic configuration, which is \([Ar] 3d^{10} 4s^1\). When it loses two electrons to become a \(+2\) ion, the resulting configuration is \([Ar] 3d^9\). This configuration indicates that there are 9 electrons in the \(\textit{d}\)\-orbitals, which are crucial for the color changes in minerals.

Electron Configuration

Understanding electron configuration is key to many phenomena in chemistry, including how minerals like malachite and azurite get their colors. Each electron configuration reflects the organization of electrons around the nucleus of an atom. In a copper(II) ion, for instance, electrons are arranged in specific orbitals.

This particular configuration \([Ar] 3d^9\) tells us there are nine electrons in the \(\textit{d}\)\-orbitals. These orbitals create specific patterns and energies. These energy levels play a pivotal role in how these minerals interact with light and thus in their displayed coloration. This configuration, particularly the partially filled \(\textit{d}\)\-orbital structure, directly impacts the minerals' ability to undergo \(\textit{d-d}\)\ transitions, which are significant to the spectrum of light that these minerals absorb and consequently, their visible color.

d-d Transition

In transition metal complexes such as those found in minerals, \(\textit{d-d}\)\ transitions are a primary source of color. These transitions occur when electrons jump between \(\textit{d}\)\-orbitals of different energy levels. Because the electron configuration of the copper(II) ion in malachite and azurite is \([Ar] 3d^9\), this means there are partially filled \(\textit{d}\)\-orbitals available for transitions.

The energy absorbed for these \(\textit{d-d}\)\ transitions falls in the visible spectrum of light. This absorption results in the minerals appearing a specific color due to the particular light wavelengths absorbed and those that are reflected. The phenomena observed in malachite and azurite stem from these \(\textit{d-d}\)\ transitions, as each mineral absorbs different light energies, correlating to their blue and green colors.

Color and Energy Relationship

Colors in minerals come from intricate interactions between light and electrons. When light hits a mineral, it can promote electrons to higher energy states. The specific energy gap that matches the wavelength of absorbed light results in colors we see.

This relationship is crucial in understanding why malachite appears green and azurite appears blue. In crystal field theory, the absorbed light causes electrons to transition between \(\textit{d}\)\-orbitals. The energy corresponding to this gap—crystal field splitting energy, denoted as \(\Delta\)—plays a central role in determining the mineral's color.

For instance, red light, which malachite absorbs, has lower energy than yellow light, which azurite absorbs. Consequently, a more substantial energy gap or splitting energy \(\Delta\) is found in azurite compared to malachite. Thus, azurite's \(\Delta\) is greater, reflecting its blue color due to the higher energy absorption. Meanwhile, malachite's green color correlates with a smaller \(\Delta\), indicating less energy absorption. This correlation between absorbed light and visible color is essential in understanding the distinct appearances of these minerals.