Chemistry, covalent bonds. explain thoroughly. i know what a covalent bond is but this don't make sense.

edit: it says an oxygen atoms has six electrons in its outermost energy level. explain why two oxygen atoms must share four electrons when they form a covalent bond

What type of interaction occurs between the r groups of valine and isoleucine in a tertiary structure? view available hint(s) what type of interaction occurs between the r groups of valine and isoleucine in a tertiary structure? salt bridge disulfide bridge hydrogen bond hydrophobic interaction