The atom with one valence electron is likely to lose its electron to form an ion with a +1 charge.
The principle behind this is simple. Atoms wish to have a stable electronic configuration, which requires that their valence shell be complete. If an atom has only one valence electron, then in order to achieve stable configuration, it is easier for it to get rid of the electron and move back to its last completed shell instead of trying to gain 7 electrons to complete the current valence shell.
