Metals include sodium, magnesium, and aluminum, to name a few. They have metallic bonding, which means that the nuclei of metal atoms are attracted to delocalised electrons, which is a form of attraction. 
The transition from sodium to aluminum: 
The number of electrons that are delocalized is increasing... 
A greater number of electrons is available to transport and carry charge across the structure... 
The electrical conductivity rises as a result of this.
I hope this helps you 
:)