Those of you who have taken an intro chemistry course, you would understand how inconceivable this bond is. It is hard to understand how two alkali metal elements can bond. To understand the enormity of this feat one must have a basic concept on how elements bond to each other.
There are several ways atoms bond, the two commonly known bonding are covalent and ionic. Covalent bonding in simply terms is when the atoms share electrons and ionic bonding is when one atom takes possession of another atoms electron.
An atom can be considered to be comprised of three subatomic elements; protons with a positive charge, neutrons with no charge and electrons with a negative charge. This is a simple breakdown of the elements of an atom as there are other elements like quarks, muons etc. As we know from charges, like charges repeal and unlike charges attract. The protons and the neutron lie in the nucleus of the atom and the electrons lie in the space surrounding the nucleus. The atom that has equal protons and electrons are considered to have a zero overall electrical charge and these atoms will have zero affinity to bond.
This is a very simplistic statement as atoms have valence shells and atoms with their outer most shell filled in addition with equal numbers of protons and electrons are called noble or inert. These elements have no affinity to bond under normal conditions.
Alkali metal elements (these are elements listed in group I on the periodic table) have the affinity to lose one electron. Normally these elements will tend to bond with halogens (these are the elements listed in group XVII). It is highly unusually for elements in the same group to bond with each other under normal conditions.
Kang Kuen Ni, a Harvard chemist achieved this feat. She formed a molecule consisting of an atom of cesium and an atom of sodium, both are alkali metals and lie in group I. They both have a lone electron in their outer most valance shell. She accomplished this feat by isolating the two atoms within a vacuum chamber with as few other atoms as possible. She directed the two atoms toward each other by use of a laser. As the electron cloud of the two atoms eclipsed, the new molecule form as the two atoms bonded together.