Why do some capacitors have polarity?

[sinanissa]

Really, after I became an electrical (control) engineer, until now i do not know why capacitors like Electrolytic and Tantalum Ones, have polarity. can anybody answer me please?

 

[mridkash]

From http://en.wikipedia.org/wiki/Electrolytic_capacitor"

"This is necessary because a reverse-bias voltage above 1 to 1.5 V[1][2][3] will destroy the center layer of dielectric material via electrochemical reduction (see redox reactions). Without the dielectric material the capacitor will short circuit, and if the short circuit current is excessive, then the electrolyte will heat up and either leak or cause the capacitor to explode."

And this explosion really happened with me once I connected a 1000 F capacitor to a car battery in reverse, it exploded, like a fire cracker!

 

[Chandra214]

The characteristics has something to do with the chemistry of holding up the charges.
In Polarised caps , the charge principle is based on electrolytics. Hence one end has to be positive and the other negative.