An excited state electron configuration describes the arrangement of electrons in an atom when one or more electrons have absorbed energy and moved to a higher energy level. This differs from the ground state configuration, which represents the most stable, lowest energy arrangement of electrons. Atoms can absorb energy from various sources, such as light, heat, or electrical discharge, prompting their electrons to transition to these higher energy states. Understanding these configurations is important for comprehending how atoms interact with light and energy.
The Nature of Electron Excitation
Electron excitation involves the movement of an electron from its usual, lower-energy orbital to a higher-energy, unoccupied orbital within an atom. This occurs when an atom gains energy from an external source. For instance, an electron can absorb a photon, or it can gain energy through a collision with another energetic particle. The energy absorbed must precisely match the energy difference between the electron’s initial, lower energy level and an available, higher energy level.
This elevated state is temporary and unstable, meaning the electron will not remain there indefinitely. The excited electron will eventually return to a lower energy level, releasing the absorbed energy, often in the form of light.
Principles of Electron Movement
Electron configurations in their ground state adhere to several fundamental principles. The Aufbau principle dictates that electrons fill the lowest available energy orbitals first. Hund’s rule states that electrons will occupy degenerate orbitals singly with parallel spins before pairing up. The Pauli exclusion principle mandates that no two electrons in an atom can have the exact same set of four quantum numbers, meaning an orbital can hold a maximum of two electrons, and those two must have opposite spins.
When an electron transitions to an excited state, some of these rules are modified. The most notable change is a violation of the Aufbau principle, as an electron moves to a higher energy orbital even when lower energy orbitals might still be available. While the Aufbau principle is no longer strictly followed, the Pauli exclusion principle still holds true. Violations of Hund’s rule can also result in excited states, such as when electrons pair up in an orbital before all degenerate orbitals are singly occupied, leading to a higher energy configuration.
Method for Determining Configuration
Determining an excited state electron configuration begins with identifying the element’s ground state electron configuration. This provides the blueprint for the atom’s electron arrangement in its most stable form. The next step involves identifying which electron will be excited. Typically, an electron from the highest occupied energy level or subshell is chosen to move, as it requires less energy to promote. One then determines the next available higher energy orbital into which this electron can transition. This new orbital must be unoccupied and represent a higher energy state than the electron’s initial position. Finally, the electron configuration is rewritten to reflect the electron’s new position in the higher energy orbital, while maintaining the total number of electrons in the atom. Atoms can have multiple possible excited states, depending on which electron is excited and to which higher energy orbital it moves.
Practical Examples
Consider a hydrogen atom, which has one electron. Its ground state configuration is 1s¹. If this electron absorbs sufficient energy, it can move from the 1s orbital to a higher energy orbital, such as the 2s orbital. The resulting excited state configuration would be 2s¹. Another possibility is for the electron to jump to the 2p orbital, yielding an excited state configuration of 2p¹.
For a carbon atom, which has six electrons, the ground state configuration is 1s²2s²2p². If one of the 2s electrons absorbs energy, it can be promoted to a 2p orbital. This would change the configuration to 1s²2s¹2p³. Alternatively, a 2p electron could be excited to a 3s orbital, resulting in an excited state configuration of 1s²2s²2p¹3s¹.
Nitrogen, with seven electrons, has a ground state configuration of 1s²2s²2p³. An excited state could arise if one of the 2s electrons moves to a 2p orbital, yielding a configuration of 1s²2s¹2p⁴. Another excited state for nitrogen might involve a 2p electron moving to a 3s orbital, leading to 1s²2s²2p²3s¹. These examples illustrate how a single electron shift to a higher energy level creates an excited state configuration.