Why do we have to use an arbitrary value such as 90% to determine the spatial limitations of an orbital?

Key Concepts

Quantum Mechanics

Quantum mechanics is the branch of physics that describes the behavior of matter and energy at atomic and subatomic levels. It introduces the concept of wave-particle duality and the uncertainty principle, which states that certain pairs of physical properties, like position and momentum, cannot be simultaneously known to arbitrary precision. This framework is essential for understanding how electrons occupy orbitals around an atom.

Atomic Orbitals

Atomic orbitals are mathematical functions that describe the probability distribution of an electron in an atom. Each orbital has a specific shape and energy level, which influences how electrons are arranged around the nucleus. The spatial limitations of an orbital are often represented by a boundary that encompasses a certain percentage of the electron's probability density, commonly set at 90%, to provide a practical way to visualize where an electron is likely to be found.

Probability Density

Probability density is a concept in quantum mechanics that quantifies the likelihood of finding a particle, such as an electron, in a particular region of space. It is derived from the square of the wave function associated with the particle. By using a threshold like 90%, chemists can define a region where there is a high probability of locating the electron, thus allowing for a more manageable understanding of electron distribution within orbitals.