oh yes, its definitely true for the halogens, they do not exist as monatomic elements for very long. When referring to "iodine" the chemist is understood to mean I2, the diatomic form, and this is also recognized when we speak of elemental bromine, we are concerning ourselves with the Br2 molecule. Monatomic Iodine is not what we refer to as being "iodine", because Iodine is I2. When we want to talk about single Iodine atoms in their elemental form, we state "monatomic iodine" ; however, we rarely if ever talk about monatomic iodine atoms, because they are unstable, basically do not exist for more than tiny fractions of a second, so we have no need to discuss monatomic iodine, it is a figment of marketers imaginations who want to offer a "new" product. Monatomic iodine has only 7 electons in its bonding shell, and it wants 8 really badly so it grabs them from anything it contacts. Look up the enthalpy of the reaction
2 I atoms -->>> I2 molecule for an appreciation of the thermodynamic driving force, which reflects the instability of monatomic iodine. Nascent chlorine is even less stable, it only lives about 100 miroseconds
Same is true for oxygen, you never find single oxygen atoms for the same reason you don't find single atoms of iodine.