What will be the atomic number of the next alkali metal to be discovered?

There are only six known alkali metal elements: lithium (Li), sodium (Na), potium (K), rubidium (Rb), caesium (Cs), and francium (Fr). The next element in that group would be #119, with a temporary name of ununennium (Uue). But most likely it would be radioactive, and decay to something else in just a few microseconds.