int timer = 1000;           
void setup() {
  for (int thisPin = 2; thisPin < 8; thisPin++) {
    pinMode(thisPin, OUTPUT);
  }
}

void loop() {
  for (int thisPin = 2; thisPin < 8; thisPin++) {
    digitalWrite(thisPin, HIGH);
    delay(timer);
    digitalWrite(thisPin, LOW);
  }
  for (int thisPin = 7; thisPin >= 2; thisPin--) {
    digitalWrite(thisPin, HIGH);
    delay(timer);
    digitalWrite(thisPin, LOW);

  }
}