Structure of Atom

Ionization Enthalpy is the energy required to remove one electron from the atom whereas electron gain enthalpy is the energy required to gain one electron from the atom

Valence Electrons is number of electrons in outermost shell whereas valency is number of electrons required for full outermost energy level

Shell has subshells which has orbitals of multiple shapes

Orbit is well-defined circular path followed by electron whereas orbital is space where probability of locating electron is high