sentences: an ion is a kind of charged particle
docs: gold_iii_ion is variable_charge_cation. copper_ion is variable_charge_cation. polyatomic_ion is ion. ion is particle. copper_ion is atomic_ion. ion is chemical_object. atomic_ion is ion. gold_ion is atomic_ion. copper_ii_ion is variable_charge_cation. gold_ion is variable_charge_cation.