According to quantum atomic model, an atom can have many possible numbers of orbitals. These orbitals can be categorized on the basis of their size, shape or orientation. A smaller sized orbital means there is a greater chance of getting an electron near the nucleus. The orbital wave function or ϕ is a mathematical function used for representing the coordinates of an electron. The square of the orbital wave function or represents the probability of finding an electron. This wave function also helps us in drawing boundary surface diagrams. Boundary surface diagrams of the constant probability density for different orbitals help us understand the shape of orbitals. Let us represent the shapes of orbitals with the help of boundary surface diagrams:

__Determination of shapes of orbitals:__

**S-orbital**: Boundary surface diagram for s orbital looks like a sphere having the nucleus as its center which in two dimensions can be seen as a circle. Hence, we can say that s-orbitals are spherically symmetric having the probability of finding the electron at a given distance equal in all the directions. The size of the s orbital is also found to increase with the increase in the value of principal quantum number (n), thus, 4s > 3s> 2s > 1s.

** P-orbitals**: Each p orbital consists of two sections better known as lobes which lie on either side of the plane passing through the nucleus. The three p orbitals differ in the way the lobes are oriented whereas they are identical in terms of size shape and energy. As the lobes lie along one of the x, y or z-axis, these three orbitals are given the designations 2p

_{x}, 2p

_{y}, and 2p

_{z}. Thus, we can say that there are three p orbitals whose axes are mutually perpendicular. Similar to s orbitals, size, and energy of p orbitals increase with an increase in the principal quantum number (4p > 3p > 2p).

__D orbital__**: **Magnetic orbital quantum number for d orbitals is given as (-2,-1,0, 1,2). Hence, we can say that there are five d-orbitals. These orbitals are designated as d_{xy}, d_{yz}, d_{xz}, d_{x}^{2}_{–y }^{2} and d_{z}^{2}. Out of these five d orbitals, shapes of the first four d-orbitals are similar to each other, which is different from the d_{z}^{2} orbital whereas the energy of all five d orbitals is same.

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