5. Sodium is a metal and sulfur is a non-metal....why we classify them this way??

Sodium is a metal as it have 1 electron to complete it's valance shell, conduct electricity and have lower electronegativities . Electronegativity is a measure of the ability of an atom in a molecule to draw bonding electrons to itself.





















Electronegativity information and above picture are from :
http://hyperphysics.phy-astr.gsu.edu/hbase/pertab/metal.html
http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bondd.html#c3

Sulfur is a non-metal as it gain 2 electrons to complete it's valance shell, does not conduct electricity and have higher electronegativities.

Group (I), (II) and (III) are metals while Group (IV), (V), (VI) , (VII), (VIII) and Group 0 are non-metal. Sodium fall on Group (I) while sulfur fall on (VI).


















Above picture is from :
http://hyperphysics.phy-astr.gsu.edu/hbase/pertab/metal.html