I bought a few months ago a brand new core i7 7700 but I have noticed on idle I get temperatures of 40-42 °C that is not a normal behavior of an i7 since during history the normal idle temperature has been of 30°C , however my main concern is that when I game the temperatures easily reach 80-84 °C. My question is that since the 7th gen is more power efficient than the 6th gen, why are the temperatures higher than the previous gen?
I wanna know if the processor is defective or something since I would like it to get replace because despite of that Intel says that "under 100°C is ok", this is no normal behavior of the CPU at all.
Actually, 40c is a perfectly normal minimum temperature. It takes liquid cooling to sustain a minimum temperature of 30c, so your idea of "normal" is way out of whack. As for a maximum in the 80-84c range, this also is perfectly normal, expected and not concerning at all (I am willing to bet that the Tcontrol temperature for your processor is right in this range).
Power efficiency has nothing to do with temperature. I repeat: nothing! Power efficiency gains are what allows 45W processors to deliver the same performance as previous generations of processors running at 90W or higher. Power efficiency gains are what allows 15W processors to deliver the same performance as previous generations of processors running at 65W.
Bottom line, your processor is not defective. It is running just fine and right within expectations. At the same time, I can say that your cooling solution is running just fine as well; maintaining temperatures at or below the processor's Tcontrol level (and thereby ensuring that it stays below the processor's thermal load line).