Valence electrons in an isolated atom can exist in either of two ways. What are they?

Unpaired valence electrons are those that do not have a partner electron sharing the same atomic orbital. These electrons are present in the outermost energy levels (shells) of an atom and are responsible for the chemical reactivity of the atom. Unpaired valence electrons can be found in atoms with odd atomic numbers or those with half-filled subshells. For example, oxygen (O), with atomic number 8, has two unpaired valence electrons in its 2p orbital.

Paired valence electrons are those that have a partner electron sharing the same atomic orbital in the outermost shell of an atom. In accordance with the Pauli Exclusion Principle, these two electrons must have opposite spins. Paired valence electrons result in atoms being more stable and less reactive compared to those with unpaired valence electrons. For example, neon (Ne), with atomic number 10, has 8 valence electrons, all of which are paired in its 2s and 2p orbitals, making neon a stable and unreactive noble gas. In conclusion, valence electrons in an isolated atom can exist in two ways: as unpaired valence electrons, which lead to higher chemical reactivity of the atom, and as paired valence electrons, which result in greater stability and lower reactivity for the atom.