Question

Objective

To learn more about the chemistry of transition and inner transition metals by using the Internet.

Be able to use your knowledge and understanding of transition metal chemistry to contribute to the discussion board.

Background

In the first and second semesters of general chemistry, there is a great deal of discussion around the Group 1A and Group 2A metals. The discussion regarding the transition and inner transition metals is much less. Transition metals and their compounds display a variety of colors. For example, when a sample of copper is held in a flame it produces a green flame test. Aqueous solutions of copper compounds are blue. Adding ammonia to copper containing solutions produces a deeper blue color.

Assignment

Choose one of the transition or inner transition metals from the periodic table.

Using your book (Chapter 23 may be very useful) and Internet resources, discuss why your transition metal and their compounds display a variety of color. Be sure to include in your discussion, important oxidation states, the electron configuration and how the d-electrons are involved.

How can you include the electromagnetic spectrum and the nature of light into your discussion? How is energy and wavelength related? Use your knowledge of the emission and absorption of light in your discussion.

Remember to site your sources in APA style.

Respond to at least two other students.

Contribute to an ongoing discussion by responding to comments made to your posting or to comments made by other students to other postings.

Answer 1

Suppose if we take

Palladium, Z= 46

Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 4d¹⁰

Reason for colored compounds of transition metals is due to the meta's interaction and bonding with ligands. All transition metals involve a five subshell d-orbital. Upon interaction with ligands, the d-orbital's five subshells are differentiated due to the instability due to electrostatic interactions with the ligand. The more unstable d-shells have higher energy state than the most stable ones. When light interacts with these compounds, the electrons present on the lower energy d orbitals absorb specific wavelengths from the white light and get excited. This results in the transfer of electrons from lower to higher energy state in the d orbital. When the electron falls back from the higher energy to the lower energy, or is de-excited, it releases a wave of the frequency corresponding to the complementary color of the absorbed color. The energy required to excite an electron or to de-excite proportional to the difference in the lower and higher energy states of the split-up d-orbitals, which in continuation is proportional to the ligand. Due to this phenomenon, transition metal compounds are colored. Palladium follows the same theoretical stance.

Energy and frequency of light are connected through Planck's constant (h), where E = h * (frequency). The energy between the d-orbital lower and higher state determine the frequency of absorbed wavelength.

Palladium compounds with colors:

palladium(II) chloride – red-brown solid and brown solution, palladium(II) oxide – black, potassium palladium(II) chloride – dark yellow or brown, ammonium palladium(II) chloride – olive green, palladium(IV) chloride complex – bright red, potassium palladium(IV) chloride - orange, palladium(II) ammine complexes – red or yellow, palladium(IV) oxide - dark red

And also we know that transition elements show variable oxidation states so the electrons will be filled differently in each case and hence during excitation and relaxing process the number of electrons varies which will excite and relax which is known as d-d transition.

For an octahedral geometry: When an electron excite from t_2g level to e_g and eg electrons relax and again come to t2g this process is known as d-d transition and it is the responsible for the color of so many transition elements.

There are other factors which are also responsible for the color of a compound and that is charge transfer, which is of two types LMCT (Ligand to Metal Charge transfer) and MLCT (Metal to Ligand Charge Transfer). Compounds like CuSO4.5H2O is colored because of charge transfer (LMCT).

The strength of ligand also affect the color of the complex since strong field ligand can start pairing in orbital and forms an inner orbital complex and show color but weak field ligands don't involve any pairing and form an outer orbital complex and don't show the color of the compound.