int timer = 1000;           // The higher the number, the slower the timing.             
void setup() {
  // use a for loop to initialize each pin as an output
  for (int thisPin = 2; thisPin < 8; thisPin++) {
    pinMode(thisPin, OUTPUT);
  }
}
void loop() {
  // loop from the lowest pin to the highest:
  for (int thisPin = 2; thisPin < 8; thisPin++) {
    digitalWrite(thisPin, HIGH);       // turn the pin on:
    delay(timer);
    digitalWrite(thisPin, LOW);       //  turn the pin off:
  }
  // loop from the highest pin to the lowest:
  for (int thisPin = 7; thisPin >= 2; thisPin--) {
    digitalWrite(thisPin, HIGH);      // turn the pin on:
    delay(timer);
    digitalWrite(thisPin, LOW);      //  turn the pin off:
  }
}