Is it accurate to say that chromium has 6 valence electrons

[anondukie]

It's electronic configuration is: 1s2 2s2 2p6 3s2 3p6 4s1 3d5

So it technically only has one electron in the outermost (n=4) shell. However, the five 3d electrons do participate in bonding and I have heard of them being referred to as valence electrons. This may sound like a question of semantics but I'd really appreciate some clarity. Thanks!

Also, how many valence electrons is Cerium ([Xe] 6s2 5d1 4f1) considered to have?

---

Members don't see this ad.

 

[anondukie]

Bump

 

[NextStepTutor_2]

Chromium is a transition metal, and you should remember that some of these have electrons in their inner shells which can be used as valence electrons, which give them their variable oxidation states. Chromium can exist as +2, +3 or +6.

Some of these elements you mention are not typically tested due to their variable behavior.

for example, Cerium is especially interesting because of its variable electronic structure. The energy of the inner 4f level is nearly the same as that of the outer (valence) electrons, and only small amounts of energy are required to change the relative occupancy of these electronic levels. This gives rise to dual valence states.

For example, a volume change of about 10 percent occurs when cerium is subjected to high pressures or low temperatures. Cesium's valence appears to change from about 3 to 4 when it is cooled or compressed. The low temperature behavior of cerium is complex.

Hope this helps, good luck!

 

[anondukie]

It definitely does! Thank you so much. I'm really grateful for the level of detail in your response!

 

[aldol16]

Applying a strict definition of valence electrons, you would consider only those in the outermost shell of the atom. But in terms of reactivity, the d electrons are definitely reactive and when metals are bonded to ligands, the s electrons are "promoted" to d orbitals so that the s-orbitals can be used for bonding (they're better because of better penetration to the nucleus). That's why Cr is actually considered a d6 complex. But this is beyond the scope of the MCAT and better suited for an organometallics course.

Do note that the chemistry of these metals is very interested and actually more diverse than all of organic chemistry. That's why organic chemists so often use metals in their syntheses and why humans use so many metals in the form of co-enzymes and co-factors - the metals can simply perform many chemical reactions that would not be possible in organics.