In full detail explain why an Iodine atom becomes an Iodide Ion. Be sure to address the following terms in your explanation: valence electrons, octet rule, and noble gases.
An iodine atom becomes an iodide ion by gaining an extra electron. To understand why this happens, we need to look at the properties of iodine and how atoms form ions.
Iodine is classified as a halogen and is located in Group 17 (Group 7A) of the periodic table. It has an atomic number of 53, meaning it has 53 protons and 53 electrons in its neutral state. These 53 electrons are distributed in different energy levels or shells around the nucleus of the iodine atom.
Valence electrons are the electrons present in the outermost energy level or shell of an atom. In the case of iodine, the outermost shell, known as the "noble gas core," is the 5s^2 5p^5 configuration. Since the noble gas before iodine is xenon (Xe) with the configuration 5s^2 5p^6, we can say that iodine has seven valence electrons.
According to the octet rule, atoms tend to gain, lose, or share electrons to achieve a stable electron configuration, similar to that of the noble gases. The noble gases are the elements in Group 18 (Group 8A) of the periodic table, and they have a completely filled outermost energy level or shell. This full outer shell configuration makes noble gases highly stable and unreactive.
In the case of iodine, as it has seven valence electrons, it is only one electron away from having a complete octet (or eight valence electrons). To achieve this stable electron configuration and resemble the noble gas xenon, iodine can gain one electron. By gaining an electron, iodine now has a total of 54 electrons, and its electron configuration becomes 5s^2 5p^6, which matches the noble gas xenon.
When an iodine atom gains an extra electron, it forms an iodide ion. The iodide ion carries a negative charge due to the extra electron, and its chemical symbol is I^-. The negative charge indicates that the ion has one more electron than protons, making it an anion.
In summary, an iodine atom becomes an iodide ion by gaining an extra electron so that it can achieve a stable electron configuration with a complete octet, similar to the noble gas xenon. This process allows the iodine atom to become more stable and have a full outermost energy level, conforming to the octet rule.