Lshell

Lshell, often written as L-shell, denotes the second electron shell of an atom, corresponding to the principal quantum number n = 2. In the classic spectroscopic notation used in early atomic theory, shells are labeled K, L, M for n = 1, 2, 3 respectively. The L-shell can hold up to eight electrons, distributed among the subshells 2s (capacity 2) and 2p (capacity 6).

In atomic structure, electrons fill shells in order of increasing energy. After the K-shell is filled, electrons begin occupying the L-shell. Elements in the second period of the periodic table have valence electrons in the L-shell, as seen in examples such as lithium (1s2 2s1), oxygen (1s2 2s2 2p4), and neon (1s2 2s2 2p6). The L-shell’s occupancy influences chemical properties, bonding behavior, and periodic trends for light elements.

The energy of the L-shell lies above that of the K-shell, and the exact energies depend on factors such as effective nuclear charge and shielding. In spectroscopy, transitions involving the L-shell can produce spectral lines in the X-ray region (the L-series), reflecting moves of electrons to or from the n = 2 level. In multi-electron atoms, the 2s and 2p subshells experience fine structure due to spin-orbit coupling and electron–electron interactions, leading to small energy separations within the L-shell.

Overall, the Lshell is a foundational concept for understanding electronic structure, chemical behavior of light elements, and certain X-ray spectral features.