1. Identify the Element:
* The electron configuration Kr 5s² tells us that the element E is in the same group as Krypton (Group 18, noble gases).
* Since it has an electron configuration ending in 5s², E is in the second row of that group.
* This element is strontium (Sr).
2. Determine the Ion Charge:
* Strontium is a Group 2 element, meaning it tends to lose 2 electrons to achieve a stable noble gas configuration.
* This results in a +2 charge: Sr²⁺
3. Determine the Fluoride Ion:
* Fluorine is a Group 17 element, meaning it tends to gain one electron to achieve a stable noble gas configuration.
* This results in a -1 charge: F⁻
4. Combine the Ions:
* To form a neutral compound, the charges of the ions must balance.
* You need two fluoride ions (2 x -1 = -2) to balance the +2 charge of the strontium ion.
5. The Formula:
* The formula for the fluoride compound of strontium is SrF₂.
