Using carbon (shown below) as an example for how to write out the electron configuration for an element: a. Write out the full electron configuration for Strontium, Sr. b. Write out the shorthand electron configuration for Strontium, Sr. For Example: The full electron configuration for the ground state element carbon is: 1s
2s
2p
. The shorthand electron configuration for carbon is [He] 2s
2p
(Note the spaces)
The Correct Answer and Explanation is:
a. Full electron configuration for Strontium (Sr):
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s
So the complete full configuration is:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s²
b. Shorthand electron configuration for Strontium (Sr):
The nearest noble gas before Strontium is Krypton (Kr), which has the atomic number 36.
So we can represent all the electrons up to Krypton using the symbol [Kr].
[Kr] 5s²
Explanation
Electron configuration is a way to represent the arrangement of electrons in an atom’s electron shells and subshells. Each element has a unique configuration based on its atomic number, which tells us how many electrons are present in a neutral atom. For Strontium (Sr), the atomic number is 38, meaning it has 38 electrons.
To write the full electron configuration, we begin filling the orbitals from the lowest energy level to the highest. The order follows the Aufbau principle:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s.
Applying this to Strontium:
- The first 2 electrons go into 1s (1s²),
- The next 2 into 2s (2s²),
- Then 6 into 2p (2p⁶),
- Followed by 2 into 3s (3s²),
- 6 into 3p (3p⁶),
- 2 into 4s (4s²),
- 10 into 3d (3d¹⁰),
- 6 into 4p (4p⁶),
- 2 into 5s (5s²),
- 10 into 4d (4d¹⁰),
- 6 into 5p (5p⁶),
- And the last 2 into 6s (6s²).
For the shorthand configuration, we use the noble gas that comes before the element. Krypton (Kr) has 36 electrons, so we write [Kr] to represent all those. After that, we add the electrons unique to Strontium: two more in the 5s orbital.
Therefore, the shorthand electron configuration for Strontium is:
[Kr] 5s²
