Final answer:
Free radicals are highly reactive atoms or molecules with an odd number of valence electrons that contain at least one unpaired electron, denoted with a dot, and are unstable. They seek stability by reacting with other atoms, often forming more stable molecules in the process. Nitric oxide (NO) is an example of an odd-electron molecule.
Step-by-step explanation:
The atoms or molecules described in the question are known as free radicals. These species have odd-electron configurations, meaning they possess an odd number of valence electrons, resulting in at least one unpaired electron. Free radicals are highly reactive due to this unpaired electron as it seeks stability by bonding with other atoms, often by taking an electron to satisfy the octet rule, or by sharing valence electrons to form covalent bonds. Nitric oxide (NO) is an example of an odd-electron molecule formed in situations such as internal combustion engines, where oxygen and nitrogen react at high temperatures. The hydroxyl radical (OH) is another example of a free radical. Because of their reactivity, free radicals play a role both as reactants and products in chemical reactions, usually reacting quickly to form more stable molecules. To denote the presence of an unpaired electron, a dot is placed in front of the chemical symbol of the radical.