The valence electrons occur in what part of the atom?
All electrons orbit the nucleus of the atom. Valence electrons are the outermost of these electrons.
The nucleus of the atom of every element consists of protons and neutrons, and the nucleus is orbited by electrons. Electrons are much smaller than protons or neutrons, and they move fast around the nucleus, essentially creating a cloud of electrons around the nucleus (atom model by Erwin Schrödinger).