A compound name is a name that describes a chemical substance. It usually consists of the element name (e.g., calcium) followed by the formula and then numerical prefixes to describe the number of atoms in the compound.
In organic compounds the order of elements is usually written with carbon first and hydrogen second, though a few exceptions occur. For example, a molecular compound with 5 carbons is named C5H5, while a molecule with 3 carbons is called C3H3.
Binary molecular compounds are also called two-elemental compounds. The element names are given in the same manner as simple ionic compounds, with the first element listed first and then the second by using the stem of the element name plus the suffix -ide.
Among alkalineearth metals magnesium forms two acetylide-type carbides, Mg2C2 and Mg2C3, both of which contain the C methanide anion. These two compounds are unique for their polar organometallic character, and are the only acetylide-type carbides containing a non-trivial [C C] group.
The ionic nature of these two compounds was first recognized about twenty years ago, and their isostructural magnesium analogue, Mg2C, is now confirmed experimentally via X-ray diffraction (Figure 1 a) and Rietveld refinement (Figure 1 c). These results reveal that Mg2C has a unique structural coordination polyhedron with a C2 dumbbell coordination number 6 forming a distorted and elongated octahedron. The symmetry of this compound is reminiscent of beryllium carbide Be2C, which has a similar ionic/covalent character.