Quote Originally Posted by Antonio1986 View Post
Please I would like also the use of "посередине" and "в середине"
"посередине" is a standalone adverb.

"в середине" is not an adverb, actually. "в середину", "из середины".

If it is about nouns rather than adverbs, there are two groups of them in Russian. "В-words" and "на-words". Probably you know about that already.

word group: being in/at - moving to - moving from
"В-words": в+<Prepositional> - в+<Accusative> из+<Genitive>
"на-words":на+<Prepositional> - на+<Accusative> с+<Genitive>