Why are sodium ions attracted to the negative electrode?

Sodium's electron configuration means that there is just one electron in its outer shell, when becoming an Ion it is easier for it to "donate" this electron to the element it is forming a compound with.

This means that the Sodium ion is no longer electrically balanced (it has lost a negatively charged electron) and becomes overall positively charged.

Being positively charged it will of cause be attracted to the NEGATIVE electrode as oposite charges attract and similar charges repel.