The quantum mechanical model of atoms provides an explanation for the stability of atoms based on the principles of quantum mechanics. According to this model, electrons in atoms occupy specific energy levels or orbitals around the nucleus. These energy levels are quantized, meaning they can only have certain discrete values.
The stability of an atom arises from the arrangement of electrons in these energy levels. The model suggests that electrons occupy the lowest available energy levels first, following a principle known as the Aufbau principle. This filling of energy levels is governed by the Pauli exclusion principle, which states that no two electrons can have the same set of quantum numbers within an atom. This means that each electron in an atom must have a unique combination of quantum numbers, including the principal quantum number, orbital angular momentum quantum number, magnetic quantum number, and spin quantum number.
The energy levels and arrangement of electrons in an atom play a crucial role in determining its stability. When all the lower energy levels are filled, electrons occupy higher energy levels. However, these higher energy levels are generally farther from the nucleus and are less stable. The electrons closer to the nucleus experience a stronger attractive force from the positively charged protons in the nucleus, which helps to balance the repulsive forces between electrons. This balance of attractive and repulsive forces contributes to the overall stability of the atom.
Additionally, the quantum mechanical model describes the concept of electron shells and subshells, which further affect the stability of atoms. Each shell corresponds to a specific principal quantum number and can contain multiple subshells. The subshells, characterized by different orbital shapes, can hold a specific number of electrons. For example, the first shell (n=1) has only one subshell, called the s subshell, which can accommodate up to two electrons. The second shell (n=2) has two subshells, s and p, with the s subshell accommodating up to two electrons and the p subshell accommodating up to six electrons.
The filled electron shells and subshells contribute to the stability of the atom by achieving a state of maximum electron density and minimizing the overall energy. The completely filled shells and subshells are particularly stable, leading to the formation of chemically inert noble gases. These atoms have their outermost shell completely filled, making them less likely to react with other elements.
In summary, the quantum mechanical model explains the stability of atoms by considering the quantized energy levels, the filling of electron orbitals according to the Pauli exclusion principle, and the balance of attractive and repulsive forces experienced by electrons. The arrangement of electrons in filled shells and subshells contributes to the overall stability of atoms, with completely filled shells resulting in particularly stable configurations.