Assign radical electrons to an atom.

It is also a combo button: the Increase lone pair tool can be selected after clicking on the black triangle in the lower-right corner of the button.

How to assign a radical electron to an atom:

Set radicals manually with the Increase radical button on the Tools toolbar. With successive clicking on the atom, you can increase the number of the radical electrons until four. For the fifth clicking all of the unpaired electrons will be removed.