Potassium, an alkali metal in group 1 of the periodic table will definitely lose an electron to a more electronegative element very easily. In fact, the potassium will effectively completely lose its electron, making it carry a +1 charge, which makes it a positive ion (a cation). A chlorine atom, which is very electronegative (due to its place in group 7 called the halogens), would happily accept the electron from the potassium, and effectively have one extra electron, leaving it with a -1 charge, making it a negative ion (an anion). When two ions form a bond together, much like the chloride ion and the potassium ion, they form an extremely strong bond called an ionic bond.
