Lithium be cut with a knife. When cut, it possesses a silvery-white color that quickly changes to gray as it oxidizes to lithium oxide. While it has one of the lowest melting points among all metals (180 °C), it has the highest melting and boiling points of the alkali metals. Lithium has a very low density (0.534 g/cm), comparable with pine wood. It is the least dense of all elements that are solids at room temperature; the next lightest solid element (potassium, at 0.862 g/cm) is more than 60% denser. Furthermore, apart from helium and hydrogen, it is less dense than
Eckart conditions better understanding of the Eckart frame it may be useful to remark that it becomes a principal axes frame in the case that the molecule is a rigid rotor, that is, when all "N" displacement vectors are zero. The "N" position vectors formula_11 of the nuclei constitute a 3"N" dimensional linear space R: the "configuration space". The Eckart conditions give an orthogonal direct sum decomposition of this space The elements of the 3"N"-6 dimensional subspace R are referred to as "internal coordinates", because they are invariant under overall translation and rotation of the molecule and, thus, depend only on the