Short Answer

An atomic orbital is a region around the nucleus of an atom where there is a high probability of finding an electron. It is not a fixed path like in Bohr’s model, but a three-dimensional area that defines where an electron is likely to be located.

Atomic orbitals help explain the arrangement of electrons in atoms, their energy levels, and how atoms form chemical bonds. Each orbital can hold a maximum of two electrons with opposite spins, and different types of orbitals (s, p, d, f) have different shapes and orientations.

Detailed Explanation :

Atomic Orbital

The concept of the atomic orbital arises from the quantum mechanical model of the atom. Unlike Bohr’s fixed circular orbits, electrons are treated as wave-particles, and their positions are described by probability distributions. An orbital represents a mathematical function derived from Schrödinger’s equation, showing where an electron is most likely to be found around the nucleus.

Types of Atomic Orbitals

Atomic orbitals are categorized based on their shape and energy level. They are denoted by the letters s, p, d, and f:

1. s-Orbital:
   • Spherical in shape
   • Present in all energy levels
   • Can hold a maximum of 2 electrons
2. p-Orbital:
   • Dumbbell-shaped, oriented along x, y, and z axes
   • Starts from the second energy level
   • Each set has 3 orbitals, holding a total of 6 electrons
3. d-Orbital:
   • More complex, cloverleaf-shaped
   • Starts from the third energy level
   • Each set has 5 orbitals, holding a total of 10 electrons
4. f-Orbital:
   • Very complex shapes
   • Starts from the fourth energy level
   • Each set has 7 orbitals, holding a total of 14 electrons

Electron Capacity of Orbitals

Each orbital can hold two electrons at most. These electrons must have opposite spins, as explained by the Pauli Exclusion Principle. The arrangement of electrons in these orbitals is described by electron configuration, which determines the chemical properties and bonding behavior of an atom.

Probability Distribution

An orbital is defined by a region of space where the probability of finding an electron is high, usually 90–95%. Unlike Bohr’s fixed orbits, the electron’s exact location cannot be determined. This probabilistic approach is central to quantum mechanics and explains the behavior of electrons more accurately.

Shapes and Orientations

• s-orbitals are spherical, meaning the electron density is uniform in all directions.
• p-orbitals are dumbbell-shaped and oriented along the three axes (px, py, pz).
• d- and f-orbitals have complex shapes and multiple orientations, influencing chemical bonding and the structure of molecules.

The shapes and orientations of orbitals explain the geometry of molecules, hybridization, and chemical bonding patterns.

Significance of Atomic Orbitals

Atomic orbitals are essential in:

1. Predicting electron configuration: Electrons fill orbitals according to the Aufbau principle, Pauli exclusion principle, and Hund’s rule.
2. Explaining chemical bonding: The overlap of atomic orbitals forms covalent bonds.
3. Understanding molecular shapes: Orbital geometry determines bond angles and molecular structure.
4. Spectroscopy: Electron transitions between orbitals explain absorption and emission spectra.

Comparison with Bohr’s Model

Unlike Bohr’s fixed circular paths, orbitals do not have definite trajectories. They provide a three-dimensional map of where electrons are likely to be. This approach is more accurate and applies to multi-electron atoms, which Bohr’s model could not explain.

Conclusion

An atomic orbital is a three-dimensional region around the nucleus where an electron is most likely to be found. It has a specific shape and energy, can hold a maximum of two electrons with opposite spins, and is fundamental to understanding electron arrangement, chemical bonding, and molecular structure. The concept of orbitals refines Bohr’s model and forms the basis of modern atomic theory.