blank ATmega328 in the UNO

hi all What will happen if I nsert a blanks ATmega328 in the UNO ? Elico

You will need to upload a boot-loader onto it using the IDE, then you can use it as normal. I think something has to be done with the reset line when uploading a new boot-loader. I think there are a few tutorials on this.

Just saw this

http://arduino.cc/en/Tutorial/ArduinoISP

Putting a blank ATmega328 will result in a board that can't do anything.

You'll need to program a bootloader on it BEFORE it can go into the board. You can use the ArduinoISP sketch with a functioning Uno to program the new chip.