Note: Some pins are not connected on a standard Arduino Uno R3 but still listed so you can use them if you had a custom board. It might also be possible that your ICSP header of the 16u2 is flipped ...

PWM: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite () function. SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication using the SPI library. LED: ...