In how many shells do the valence electrons of iodine lie?

The valence electrons of iodine are found in a total of **four shells**. To understand this better, let’s break down the concept of electron shells and how they relate to iodine specifically.

Understanding Electron Shells

Electron shells are layers around an atom's nucleus where electrons reside. Each shell can hold a certain number of electrons, and they are filled in a specific order based on energy levels. The shells are designated by principal quantum numbers (n), starting from n=1 for the shell closest to the nucleus.

Iodine's Electron Configuration

Iodine has an atomic number of 53, meaning it has 53 electrons. The electron configuration of iodine can be written as:

• 1s² 2s² 2p⁶
• 3s² 3p⁶
• 4s² 3d¹⁰ 4p⁵

This configuration shows how the electrons are distributed across the various shells:

• **First shell (n=1)**: 2 electrons (1s²)
• **Second shell (n=2)**: 8 electrons (2s² 2p⁶)
• **Third shell (n=3)**: 18 electrons (3s² 3p⁶ 3d¹⁰)
• **Fourth shell (n=4)**: 5 electrons (4s² 4p⁵)

Identifying Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom that are involved in chemical bonding. For iodine, the outermost shell is the fourth shell (n=4), which contains 7 electrons (2 from 4s and 5 from 4p). Therefore, while the total number of shells is four, the valence electrons specifically reside in the fourth shell.

Summary of Iodine's Valence Electrons

In summary, iodine has its valence electrons in the fourth shell, and there are a total of four electron shells surrounding its nucleus. This arrangement is crucial for understanding iodine's chemical behavior, particularly its tendency to gain one electron to achieve a stable octet configuration.