Final answer:
The electron configuration for an atom with 20 electrons (calcium) is 1s² 2s² 2p¶ 3s² 3p¶ 4s². The electron configuration is determined using the aufbau principle, Pauli exclusion principle, and Hund's rule.
Step-by-step explanation:
To write the electron configuration of an atom with 20 electrons, you'll follow the order of orbital filling prescribed by quantum mechanics. An atom with 20 electrons is the element calcium (Ca). We'll use the aufbau principle, Pauli exclusion principle, and Hund's rule to determine the electron configuration.
The first two electrons will fill the 1s orbital (1s2), next two electrons will fill the 2s orbital (2s2). The next six electrons will fill the 2p orbitals (2p6), then two more in the 3s (3s2). After filling the 3s, the next six electrons will fill the 3p orbitals (3p6).
Finally, the remaining two electrons will go into the 4s orbital (4s2), giving us the full configuration for calcium:
Electron Configuration for Calcium (Ca): 1s2 2s2 2p6 3s2 3p6 4s2.