seconds.ino

const int numPins = 12;
const int pins[] = {2,3,4,5,6,7,8,9,10,11,12,13};

void setup() {
  for (int i = 0; i < numPins; ++i) {
    pinMode(pins[i], OUTPUT);
  }
}

int litPin = 0;

void loop() {
  digitalWrite(pins[litPin], LOW);
  litPin = (litPin + 1) % numPins;
  digitalWrite(pins[litPin], HIGH);
  delay(1000);
}