The electron configuration for the strontium ion (Sr²⁺) is [Kr] or 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶. To understand how we arrive at this, let’s break it down:
Strontium (Sr) is located in group 2 of the periodic table and has an atomic number of 38. This means a neutral Sr atom has 38 electrons. The electron configuration of a neutral strontium atom is:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
This accounts for all 38 electrons. However, when strontium forms a Sr²⁺ ion, it loses two electrons. Typically, these electrons are removed from the outermost shell, which is the 5s orbital in this case. Therefore:
- Start with the neutral Sr electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
- Remove two electrons from the 5s orbital (which is actually the 4s for Sr): 1s² 2s² 2p⁶ 3s² 3p⁶
(now we’re only left with 36 electrons).
This results in an electron configuration of [Kr], indicating that the Sr²⁺ ion has the same electron configuration as the noble gas krypton. This stable electron configuration is the reason strontium commonly forms a +2 ion.