All practice pages/Interatomic theory/Elements
Element 65, a lanthanide
A rare earth from the Ytterby quarry whose compounds glow a vivid green.
Period 6, in the lanthanide row set below the main table. The other lanthanides are tinted, and every cell opens its own article.
Terbium has 65 electrons, one for every proton, so the atom carries no charge. Below are the same 65 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁹ 5s² 5p⁶ 6s²
Short form: [Xe] 4f⁹ 6s², where [Xe] stands for the 54 electrons xenon already has.
That list runs by shell. In the order the subshells fill it reads [Xe] 6s² 4f⁹, because a subshell fills by its energy, not by its shell number.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 4 here is 4s² 4p⁶ 4d¹⁰ 4f⁹, and 2 + 6 + 10 + 9 is 27.
Terbium sits in period 6 and has 6 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones terbium can lose, gain or share, so they are the ones that decide what it bonds with.
Like the other lanthanides, it gives up three electrons to form the Tb³⁺ ion in most of its compounds.
One of the rarer rare earths, found in xenotime, monazite and the ion-adsorption clays of southern China.
Carl Gustaf Mosander found it in 1843 in yttria from Ytterby, together with erbium, and both were named after the village. The two names were later swapped by mistake, and the swap stuck.
Green phosphors in fluorescent lamps and screens; Terfenol-D, an alloy that changes shape in a magnetic field and drives sonar and precision actuators; and small additions to neodymium magnets that must work in hot motors.