be determined or known accurately. That is why, as you shall see later on, one talks of only probability of finding the electron at different points in an atom. . An atomic orbital is the wave function ψ for an electron in an atom .
Whenever an electron is described by a wave function, we say that the electron occupies that orbital. Since many such wave functions are possible for an electron, there are many atomic orbitals in an atom. These “one electron orbital wave functions” or orbitals form the basis of the electronic structure of atoms. In each orbital, the electron has a definite energy.
An orbital cannot contain more than two electrons. In a multi-electron atom, the electrons are filled in various orbitals in the order of increasing energy. For each electron of a multi-electron atom, there shall, therefore, be an orbital wave function characteristic of the orbital it occupies. All the information about the electron in an atom is stored in its orbital wave function ψ and quantum mechanics makes it possible to extract this information out of ψ .
. The probability of finding an electron at a point within an atom is proportional to the square of the orbital wave function i.e., | ψ | at that point. | ψ | is known as probability density and is always positive. From the value of | ψ | at different points within an atom, it is possible to predict the region around the nucleus where electron will most probably be found.
. . Orbitals and Quantum Numbers A large number of orbitals are possible in an atom. Qualitatively these orbitals can be distinguished by their size, shape and orientation.
An orbital of smaller size means there is more chance of finding the electron near the nucleus. Similarly shape and orientation mean that there is more probability of finding the electron along certain directions than along others. Atomic orbitals are precisely distinguished by what are known as quantum numbers. Each orbital is designated by three quantum numbers labelled as n, l and m l