According to Pauli Exclusion Principle This states that no two electrons in an atom can have the exact same four electronic properties. quantum numbers
. An orbital can only contain two electrons. Therefore, they must have opposite spins. This means that if one electron is given an up-spin (+ 1/2), the other must have a down-spin (+ 1/2).
This is because an electron’s spin creates a magnetic field. If electrons with opposite spins are grouped together, there will be no net magnetic field as the negative and positive spins cancel one another out. An odd number of electrons in an atom will determine its spin.