Tuumalaengu

Tuumalaengu, or nuclear charge, is the total positive electric charge located in the nucleus of an atom. It is denoted by Z and equals the number of protons in the nucleus. Each proton carries a charge of +e, so the nucleus has a net charge of Ze in units of the elementary charge. Neutrons do not contribute to the nuclear charge, and electrons are external to the nucleus.

The nuclear charge largely determines the electrostatic attraction between the nucleus and the atom’s electrons. In simple models, an electron in a given orbital feels an effective nuclear charge Z_eff that is smaller than Z due to shielding by inner electrons. Z_eff can be estimated by rules such as Slater's rules; more sophisticated calculations use quantum-mechanical methods.

Consequences: as Z increases across a period, outer electrons experience a higher Z_eff, leading to smaller atomic radii and higher ionization energies; down a group, shielding effects limit changes in Z_eff. The concept underpins periodic trends and helps explain spectral line separations in hydrogen-like systems and multi-electron atoms.

Applications and related usage: Nuclear charge is a fundamental parameter in atomic and nuclear physics; it influences energy levels, ionization energies, and chemical bonding. In nuclear physics, a higher Z increases the Coulomb barrier between protons, affecting nuclear stability and reaction rates. In Estonian, the term tuumalaeng denotes nuclear charge, with the genitive form tuumalaengu.