My two cents:
If the title is a full grammatical sentence (usually a question), I prefer the use of sentence case:
Why does this alkene addition reaction lead to a racemized mixture of products?
If the title is not a full grammatical sentence, but is more of a descriptive phrase, I prefer the use of title case:
Racemized Products in Alkene Addition Reactions
I've found both approaches to be preferable in different circumstances, so I wouldn't personally advocate for one over the other as a general principle.
Element names are common nouns; as such, their capitalization patterns should be identical to any other common noun:
Thiol Affinities of Silver and Gold
Why does gold commonly exhibit both the +1 and +3 oxidation states, but silver only the +1?