The alkali metals in group l of the periodic table all have a single electron in the outermost shell. These metals form covalent bonds with for example the halogens, which have 7 electrons in their outer shell.
When the alkali metal halide, such as KCl is dissolved in water, it dissociates into ions. The K atom loses the single electron, and therefore has a positive charge. In turn, the chloride atom gains the electron and becomes the negatively charged chloride ion.
