An organometallic fragment that is isolobal to CH3 is...

A. Fe(Co)s
B. Mn(Co)s
C. Cr(Co)s
D. Ni(Co)s
I don't understand!

To determine the organometallic fragment that is isolobal to CH3, we need to understand what isolobal means in organometallic chemistry.

Isolobal is a term used to describe two fragments or complexes that have the same number of valence electrons and similar electronic structures, despite having different elements. In other words, the isolobal fragments can be conceptualized as being derived from the same parent molecule by replacing one atom or group with another while keeping the overall electronic structure intact.

In the case of CH3, we have a carbon atom bonded to three hydrogen atoms. To find the isolobal fragment, we need to look for the metal fragment that has the same number of valence electrons and a similar electronic structure.

To determine the number of valence electrons in CH3, we consider that carbon contributes 4 valence electrons, and each hydrogen contributes 1 valence electron. Therefore, CH3 has a total of 4 + 3(1) = 7 valence electrons.

Now let's examine the options given:

A. Fe(Co)s: Here, Fe is iron, which has an electron configuration [Ar]3d64s2. Since Fe is in the 8th group of the periodic table, it has 8 valence electrons. Co is carbon monoxide, which has 2 valence electrons. Therefore, Fe(Co)s has a total of 10 valence electrons.

B. Mn(Co)s: Here, Mn is manganese, which has an electron configuration [Ar]3d54s2. Since Mn is in the 7th group of the periodic table, it has 7 valence electrons. Co is carbon monoxide, which has 2 valence electrons. Therefore, Mn(Co)s has a total of 9 valence electrons.

C. Cr(Co)s: Here, Cr is chromium, which has an electron configuration [Ar]3d54s1. Since Cr is in the 6th group of the periodic table, it has 6 valence electrons. Co is carbon monoxide, which has 2 valence electrons. Therefore, Cr(Co)s has a total of 8 valence electrons.

D. Ni(Co)s: Here, Ni is nickel, which has an electron configuration [Ar]3d84s2. Since Ni is in the 10th group of the periodic table, it has 10 valence electrons. Co is carbon monoxide, which has 2 valence electrons. Therefore, Ni(Co)s has a total of 12 valence electrons.

Based on the number of valence electrons, the isolobal fragment that is most similar to CH3 (which has 7 valence electrons) is Cr(Co)s (which also has 7 valence electrons). So the correct answer is C.