Members of which group of elements lose one electron to form cations with a +1 charge?
These elements are known as the alkali metals. They are found in the column on the extreme left of the table,
The alkali metals share an important structural feature - each has one valence electron (one electron in its outermost shell).
This electron is quite weakly bound to the nucleus of the atom, and as a result, little energy is needed to remove it. This explains why these elements readily undergo reactions with chemicals that are electrophilic ("looking for electrons").
When the valence electron is removed, the particle that remains is a positive ion, with a +1 charge, as mentioned in the question.