int ledPins[] = {2,3,4,5,6,7,8,9};
  int pinCount=8;
   int timer=100;

void setup() {

  for(int thisPin=0 ;thisPin<pinCount ;thisPin++){
    pinMode(ledPins[thisPin],OUTPUT);

  }

}

void loop() {

for(int thisPin = 0; thisPin < pinCount; thisPin++){
   
    digitalWrite(ledPins[thisPin], HIGH);
    delay(timer+(thisPin*10)); 

    digitalWrite(ledPins[thisPin], LOW);
  }
  
  for(int thisPin = pinCount -1; thisPin >= 0; thisPin --){

  digitalWrite(ledPins[thisPin], HIGH);
  delay(timer);

  digitalWrite(ledPins[thisPin], LOW);
}
}