In the modern atomic model, electrons are arranged in shells (or energy levels) and subshells (s, p, d, f, ...) around a nucleus composed of protons and neutrons. The maximum number of electrons for shell \(n\) is approximated by: \[ 2n^2. \] When an electron jumps between shells, it emits or absorbs a photon whose energy is: \[ \Delta E = h \,\nu, \] where \(h\) is Planck's constant and \(\nu\) is the frequency of the radiation. Additionally, each electron has an intrinsic angular momentum called spin, which can be represented as ‘up’ (\(\uparrow\)) or ‘down’ (\(\downarrow\)).