The subatomic particle with a negative charge is the electron. This particle was first identified in 1897.
Electrons play an important role in determining the reactivity of an atom. Reactivity, which refers to an atom's ability to form bonds with other atoms, is determined by the number of electrons an atom has in its outer shell. Atoms with eight electrons in the outer shell do not react with other atoms, making them stable. Atoms with one, two, three, or seven electrons in the outer shell are the most reactive.
Chemical bonds form between atoms that give up, gain, or share electrons, forming stable compounds. For example, sodium chloride forms when sodium gives up an electron and chlorine gains an electron.