While I3- and Br3- are both stable molecules F3- is not a stable molecule. Provide an explanation.
To explain why I3- and Br3- are stable molecules while F3- is not, we need to consider their electronic configurations and the concept of chemical bonding.
Iodine (I) and bromine (Br) both belong to Group 17 (Group VIIA), also known as the halogens, on the periodic table. They have similar electronic configurations, with seven valence electrons in their outermost shell. To achieve a more stable electron configuration, they tend to gain one electron (in the case of I) or two electrons (in the case of Br) to achieve a full octet (eight valence electrons).
This electron gain is achieved through a process called ionic bonding. I3- and Br3- molecules are formed when the halogen atoms, I or Br, combine with three additional electrons, forming stable halide ions (I- and Br-). These ions have achieved a stable octet electron configuration by gaining electrons.
Now, let's come to fluorine (F), which is also a halogen. Fluorine has seven valence electrons like iodine and bromine. However, gaining three electrons to achieve a stable octet is highly unfavorable for fluorine because it requires a significant amount of energy to accommodate those additional electrons in its compact atomic structure.
Instead, fluorine forms very stable compounds by sharing one electron with other atoms through covalent bonding. In a covalent bond, atoms share electrons to achieve a complete outer electron shell. Fluorine typically forms single covalent bonds (F-) or sometimes double covalent bonds (F=) with other elements, rather than gaining three electrons through ionic bonding.
In summary, I3- and Br3- are stable because they achieve a stable octet configuration through ionic bonding, by gaining one or two electrons, respectively. On the other hand, F3- is not a stable molecule because fluorine prefers to form single or double covalent bonds, sharing electrons with other atoms rather than gaining three electrons.