I'd like to suggest that presents, gifts, and rewards like that should not be the goal. To give him a gift after a week of behaving politely is sending a missed message. There has got to be a more substantial, life-long reward. Those can be things like time spent with parents, a pleasant evening playing a game together, peacefulness in the home, a little freedom due to having earned your trust.
There are many times in life where we do what's right and don't get a reward, or a gift, or money. Think of the times that you are driving somewhere, and you obey the speed limit, observe the stop signs, stay in your lane, etc. While you might get a ticket for NOT doing those things, doing them means you get the freedom of driving, of independence, of being able to drive your car to meet your friends for dinner, etc. The police don't stop you for driving carefully and hand you money. Same with getting an education - someone in college studies hard, pays attention, shows up for class, not because they get a prize for the day, but because it means they'll be able to choose a career, get a good job, provide for themselves. You're kind of teaching your child that good behavior equals toys or electronics. Instead, teach him that good behavior means that mom and dad are smiling, you all get to go on a bike ride together, dad sits down and does a puzzle with him, mom doesn't have a headache, he lives in a peaceful home.
Getting his attention by a "pop in the mouth" certainly accomplishes that, but it would be better to get his attention by interacting with him, talking, joking, learning about something he's interested in, when he is NOT misbehaving. He may be feeding off this drama, seeing you so angry, seeing you react. Try completely ignoring him when he's misbehaving, and making eye contact and talking calmly when he's behaving.
If he's truly not learning anything, and if he has mastered the curriculum already, then enroll him in something. Karate, gymnastics, computer coding for kids online, whatever. Stretch his mind. Engage him.
And make sure to stress the difference between discipline and punishment. Discipline is teaching, like saying to a 2 year old "before we cross the street, you will hold Mommy's hand so you will be safe". Punishment is "you let go of Mommy's hand so we will not be going to cross the street for ice cream. Next time if you continue to hold my hand we can cross the street and get that ice cream". And make sure you're not ever using words like "snot" or "pop you in the mouth". Stay calm, restrict him from viewing any reaction on your part, and explain what he did wrong. Make sure your rules are clear and concise, and understood beforehand. Post them in a prominent place. Establish the punishments.
I hope your whole family can get some counseling and help your son.