Yes, bromine (Br) is indeed smaller than iodine (I).
Understanding Atomic Size
The size of an atom, often quantified by its atomic radius, is primarily determined by two factors: the number of electron shells and the nuclear charge. As you move down a group in the periodic table, atoms generally become larger. This trend is clearly observed within Group 17, the halogens, which include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).
Key Factors Influencing Atomic Size:
- Number of Electron Shells: Atoms with more electron shells will naturally have a larger atomic radius because their outermost electrons are further from the nucleus. Each new shell adds a significant increase in size.
- Nuclear Charge (Protons): A greater number of protons in the nucleus exerts a stronger pull on the electrons, tending to pull them closer to the nucleus and reduce the atomic size. However, the effect of added electron shells usually dominates over the increased nuclear charge when moving down a group.
Bromine vs. Iodine: A Comparison
Iodine is located below bromine in Group 17 of the periodic table. This means that iodine has an additional electron shell compared to bromine.
- Bromine (Br): Has electrons occupying 4 electron shells.
- Iodine (I): Has electrons occupying 5 electron shells.
Because iodine has more electron shells, its outermost electrons are situated at a greater distance from the nucleus than those in bromine. This expanded electron cloud results in iodine having a significantly larger atomic radius. The presence of these added shells of electrons is the fundamental reason why iodine's atomic radius is larger than that of bromine, as well as fluorine and chlorine.
Atomic Radius Comparison
The following table illustrates the atomic radii of selected halogens, highlighting the increase in size down the group:
| Element | Symbol | Atomic Number | Period | Approximate Atomic Radius (pm) |
|---|---|---|---|---|
| Fluorine | F | 9 | 2 | 50 |
| Chlorine | Cl | 17 | 3 | 100 |
| Bromine | Br | 35 | 4 | 115 |
| Iodine | I | 53 | 5 | 140 |
Note: Atomic radii can vary slightly depending on the measurement method (e.g., covalent, van der Waals).
This data clearly shows that bromine's atomic radius (approximately 115 pm) is smaller than iodine's (approximately 140 pm). This trend is consistent with the periodic table's organization, where elements in lower periods of the same group possess more electron shells, leading to larger atomic sizes.
For further exploration of atomic radius trends, refer to resources like Khan Academy's explanation of atomic radius trend.
