bool ledOn = true;
const unsigned long deltaT = 100;

void setup() {
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
  pinMode(7, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
}

void loop() {
  digitalWrite(2, ledOn ? HIGH : LOW); delay(deltaT);
  digitalWrite(3, ledOn ? HIGH : LOW); delay(deltaT);
  digitalWrite(4, ledOn ? HIGH : LOW); delay(deltaT);
  digitalWrite(5, ledOn ? HIGH : LOW); delay(deltaT);
  digitalWrite(6, ledOn ? HIGH : LOW); delay(deltaT);
  digitalWrite(7, ledOn ? HIGH : LOW); delay(deltaT);
  digitalWrite(8, ledOn ? HIGH : LOW); delay(deltaT);
  digitalWrite(9, ledOn ? HIGH : LOW); delay(deltaT);
  ledOn = not ledOn; // flip the led state
  delay(500);
}