Which is not a ground state electron configuration?
A. 1s2
B. 1s2 2p1
C. 1s2 2s2
D. 1s2 2s2 2p1
To determine which electron configuration is not a ground state configuration, we need to understand what a ground state configuration is.
The ground state electron configuration represents the lowest energy arrangement of electrons in an atom. Electrons fill the available orbitals in order of increasing energy, following the Aufbau principle (filling up orbitals from lower to higher energy levels).
Let's examine each option and determine which one violates the ground state configuration:
A. 1s2 - This is the ground state electron configuration for helium (He).
B. 1s2 2p1 - This is the ground state electron configuration for boron (B). The electron occupies the 2p orbital after filling the 1s and 2s orbitals.
C. 1s2 2s2 - This is the ground state electron configuration for beryllium (Be). The 2s orbital is filled after the 1s orbital.
D. 1s2 2s2 2p1 - This is not a ground state electron configuration because it violates the Aufbau principle. According to this principle, the 2p orbital should not be occupied until after the 2s orbital is filled. So, this configuration is not a valid ground state configuration.
Therefore, the correct answer is D. 1s2 2s2 2p1.