The G-block is a hypothetical section of the periodic table that chemists have yet to discover. It should start around Unbiunium, element 121, and end around Unquadnilium, element 140.
If the trend of the previous rows continued, then the g-block would have eighteen elements. However, calculations predict a very strong blurring of patterns in the eighth period, to the point that individual blocks become hard to stand out. It is likely that the eighth period will not quite follow the trend of previous rows.