The octet rule isn't an actual rule and it only really applies to the first group of atoms. Once an atom has electrons in the d-shell, this "rule" goes out the window. The atom can essentially shove extra electrons in this shell, allowing it to have more than the four bonds, such as SF6. With regard to covalent bonds, the two atoms each contribute an electron to the bond and it counts as two for each of them. For instance, with fluorine, which only has one extra electron, it contributes this electron in a covalent bond with, say, hydrogen, and you count it as having both its electron and the electron from hydrogen. Once you get to the d-shells, however, this is all out the window.

[Xe]6s²4f⁴ (Neodymium) is too heavy of an atom to have the octet "rule" apply. Typically the octet rule is used to describe the association of lighter atoms that have only s and p orbitals involved in covalent bonding (for the record it's ns²np⁶). 2 electrons in the s subshell and 6 for the p make a full octet and achieve a noble gas configuration. As Ame mentioned, atoms will covalently "share" electrons in order to have both of them get to this stable state.

There are numerous violations to the octet rule of course, making it more of a rule of thumb than an absolute.

 

Two covalently bonded atoms share a pair of electrons in their outer shell.  Each atom contributes one electron to an electron pair, basically adding one electron to their outer shell in the process.

What is your question regarding Xenon?