Valence electrons

[Jwinsler7]

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This Q is from AAMC #5.

Electrons in which of the following orbitals of Ti can form bonds with substance X?
A) 2s
B) 3d
C) 4p
D) 5f

I chose the correct answer, B. Ti has e' configuration of [Ar]4s2 3d2
First of all, I am wondering if choice A had been 4s instead of 2s, then option A could've been correct as well?

Secondly, are both sets of electrons in 4s2 and 3d2 considered to be valence electrons for Ti? Or is it just 4s2 since they are the outermost electrons?

 

[LoLCareerGoals]

I think if I remember correctly 4s are lower energetically then 3d, so if the question asked for which orbital would donate el-ons first if we were to form Ti+, then I'd say the answer is 4s.
As for bonding, 3d is an obv answer choice among those 3, but can you elaborate? Is it an ionic bond (I am guessing so since it is a metal, but who knows)?

I am pretty sure Ti exists with 3+ oxidation number in different compounds so both s and d must be participating in the bonding in those cases.

 

[gtbROX]

Bonding ability, or reactivity, is greatest when the electrons are in higher energy (further from the nucleus, higher shell #) orbitals. The highest orbital that contains electrons (of the answer choices) is the 3d.

2s is not available for bonding because it is complete in itself and as such is too stable/low energy to be accessed, and you'd have to bump through the 3d electrons just to touch them. The better answer would have been 4s because you always ionize/react with the higher shell electrons first, but that answer choice doesn't exist.

 

[Jwinsler7]

Are both sets of electrons in 4s2 and 3d2 considered to be valence electrons for Ti? Or is it just 4s2 since they are the outermost electrons?

 

[shaboobly]

Are both sets of electrons in 4s2 and 3d2 considered to be valence electrons for Ti? Or is it just 4s2 since they are the outermost electrons?

i think 4s would be considered valence more so than 3d because those electrons are in the n=4 level, which is the shell where electrons are ionized from in this period, and depending on the element.

pretty sure it all depends on the n value.

 

[Jwinsler7]

But, from what I understand 4s and 3d energy level are so close from each other, hence both sets are considered to be valence electrons? I would like a definite answer for this one. Anyone?

 

[LoLCareerGoals]

Why are you getting hung up on this? Who cares what human made label you put on this el-on vs that one. You know their energy levels with respect to each other you know the answer to the question.
You couldn't possible want a "definitive" answer that bad because a simple google search gets this on a 2nd hit: http://dl.clackamas.cc.or.us/ch104-06/valence_electrons.htm.
It lists Ti as having 2-4 valence electrons. So what? What did that help? From source above:
"As it turns out, the idea of valence electrons is not very useful for transition metals, at least not in a reliable, predictable way."
Yes it would be confusing if they listed 4s as one of the answers as well. Then I would choose highest energy one as an answer.

 

[shaboobly]

But, from what I understand 4s and 3d energy level are so close from each other, hence both sets are considered to be valence electrons? I would like a definite answer for this one. Anyone?

it doesnt matter how close in energy they are because the 4s shell's wavefunction provides a larger radius than a 3d, which means the n=4 shell is the most accessible and is where the electrons, most of the time, come from when the metal is ionized.

the energy only matter, as in n+l, when you are filling orbitals because after all, you want to have the lowest energy configuration.

 

[Jwinsler7]

Thanks for clarification