real time clck -RTC DS 1307- to Arduino
It won't work if there are no pullups on the lines, because I2C uses an open drain bus. 

Add a 2.2k&Omega; resistor (can be anything between this and 10k&Omega;, a lower value is better for long lines and higher clock speed) from SCL to +5V and also another one from SDA to +5V (so one between DS1307 pins 5 and 8, another one between pins 6 and 8) .   

The resistors (marked Rp) are shown below:



If you need the square wave out, you will also need a pullup on this too, details are in the datasheet.