I would like to ask how many valence electrons took part in creating chemical bond in $\ce{OH-}$? Is the minus related to $\ce{O}$ or to $\ce{H}$? Are there any spare valence electrons which didnt take part in creating chemical bond in $\ce{OH-}$?
In the photo the orange electrons are non bond electrons.
And the black electrons are bond electrons.
There are 2 electrons took part in creating chemical bond in $\ce{OH}$.
The first one is from oxygen.
The second is from hydrogen.
This kind of bond is called "Covalent bond". For more about Covalent bond : https://en.wikipedia.org/wiki/Covalent_bond
The minus is related to the black and white electrons that are free (in Oxygen).
The white electron is come from other element.