Question

prepwork part 1: electron configuration practice
complete the ground - state orbital energy level diagrams and write the corresponding electron configurations for all of the following elements:

1. *magnesium
2. chlorine
3. **argon
4. using what you know about orbital diagrams and the beginning of the orbital diagram below, create an orbital diagram for calcium. (hint: you may need to add boxes!)

reference the models on page 3 in your student handout to answer the following questions.

1. **the lowest potential energy arrangement of electrons in an atom is called the ground state (how atoms are normally found). ground - state electron configurations can be predicted by a strict set of rules; one is known as the aufbau principle (\aufbau\ means filling up). examine the diagrams in the model and the statements below to determine the phrase that best describes each rule. circle the correct answer.

a. *based on where a single electron is placed, the lowest potential energy electron in an atom is found in the ______ sublevel.
1s 2s 3s

Explanation:

Step1: Recall electron - filling rules

Use the Aufbau principle (fill lower - energy orbitals first), Pauli exclusion principle (each orbital can hold at most 2 electrons with opposite spins), and Hund's rule (electrons occupy degenerate orbitals singly before pairing).

Step2: Determine electron numbers

• Magnesium (Mg) has an atomic number of 12, so it has 12 electrons.
• Filling order: 1s²2s²2p⁶3s². The orbital diagram: 1s has 2 paired electrons, 2s has 2 paired electrons, 2p has 6 electrons (3 pairs in 3 orbitals), 3s has 2 paired electrons.
• Chlorine (Cl) has an atomic number of 17, so it has 17 electrons.
• Filling order: 1s²2s²2p⁶3s²3p⁵. The orbital diagram: 1s has 2 paired electrons, 2s has 2 paired electrons, 2p has 6 electrons (3 pairs in 3 orbitals), 3s has 2 paired electrons, 3p has 5 electrons (2 pairs and 1 unpaired in 3 orbitals).
• Argon (Ar) has an atomic number of 18, so it has 18 electrons.
• Filling order: 1s²2s²2p⁶3s²3p⁶. The orbital diagram: 1s has 2 paired electrons, 2s has 2 paired electrons, 2p has 6 electrons (3 pairs in 3 orbitals), 3s has 2 paired electrons, 3p has 6 electrons (3 pairs in 3 orbitals).
• Calcium (Ca) has an atomic number of 20, so it has 20 electrons.
• Filling order: 1s²2s²2p⁶3s²3p⁶4s². The orbital diagram: 1s has 2 paired electrons, 2s has 2 paired electrons, 2p has 6 electrons (3 pairs in 3 orbitals), 3s has 2 paired electrons, 3p has 6 electrons (3 pairs in 3 orbitals), 4s has 2 paired electrons.

Step3: Answer question 8a

The lowest potential energy electron in an atom is found in the 1s sublevel according to the Aufbau principle which fills the lowest - energy orbitals first.

Answer:

Magnesium: Orbital diagram: 1s (2 paired electrons), 2s (2 paired electrons), 2p (3 pairs), 3s (2 paired electrons); Electron configuration: 1s²2s²2p⁶3s²
Chlorine: Orbital diagram: 1s (2 paired electrons), 2s (2 paired electrons), 2p (3 pairs), 3s (2 paired electrons), 3p (2 pairs and 1 unpaired); Electron configuration: 1s²2s²2p⁶3s²3p⁵
Argon: Orbital diagram: 1s (2 paired electrons), 2s (2 paired electrons), 2p (3 pairs), 3s (2 paired electrons), 3p (3 pairs); Electron configuration: 1s²2s²2p⁶3s²3p⁶
Calcium: Orbital diagram: 1s (2 paired electrons), 2s (2 paired electrons), 2p (3 pairs), 3s (2 paired electrons), 3p (3 pairs), 4s (2 paired electrons); Electron configuration: 1s²2s²2p⁶3s²3p⁶4s²
8a. 1s