The noble gas configuration for Br
The Correct Answer and Explanation is:
The noble gas configuration for bromine (Br) is:
[Ar] 3d¹⁰ 4s² 4p⁵
Explanation
To determine the noble gas configuration for bromine, it helps to understand its position on the periodic table and the concept of noble gas shorthand notation. Bromine, with the atomic number 35, has 35 electrons. In shorthand notation, we express electron configurations by using the closest preceding noble gas configuration as a starting point, followed by the remaining electron configuration specific to the element.
- Identify the Previous Noble Gas: For bromine, the noble gas that comes before it is argon (Ar), with an atomic number of 18. Therefore, argon’s electron configuration, which is 1s² 2s² 2p⁶ 3s² 3p⁶, can be used as the base. This is written as [Ar].
- Determine Additional Electrons: After argon, we still need to account for 17 more electrons to reach bromine’s total of 35. We add these electrons in the following order:
- 3d subshell: 10 electrons fill the 3d orbital completely, giving 3d¹⁰.
- 4s subshell: The next two electrons go into the 4s orbital, giving 4s².
- 4p subshell: The remaining five electrons occupy the 4p orbital, giving 4p⁵.
- Resulting Configuration: When we combine all parts, the noble gas configuration for bromine becomes [Ar] 3d¹⁰ 4s² 4p⁵.
Why Noble Gas Configurations Are Useful
Noble gas configurations are a streamlined way of expressing electron arrangements. They simplify complex configurations by focusing only on valence electrons, which play a primary role in chemical behavior. For bromine, the configuration 4s² 4p⁵ shows that bromine has seven valence electrons (in the fourth energy level), similar to other halogens, which need only one more electron to reach a stable, filled shell. This explains bromine’s reactivity and tendency to form bonds by accepting an electron, particularly in ionic compounds or covalent bonding situations.