Electronic Configuration and Principles Quiz

What does the Aufbau Principle state?

• Electrons fill the lowest available energy levels first

• Electrons fill higher energy levels first

• Electrons occupy orbitals singly before pairing up

• Electrons fill subshells in random order

Answer explanation

The Aufbau Principle states that electrons fill the lowest available energy levels first, ensuring that the most stable configurations are achieved before higher energy levels are occupied.

Which of the following is the correct electronic configuration of oxygen (atomic number 8)?

• 1s² 2s² 2p⁴

• 1s² 2s² 2p²

• 1s² 2s¹ 2p⁵

• 1s² 2s² 2p⁶

Answer explanation

Oxygen has an atomic number of 8, meaning it has 8 electrons. The correct electronic configuration is 1s² 2s² 2p⁴, which accounts for all 8 electrons, with 2 in the 1s, 2 in the 2s, and 4 in the 2p subshell.

What is the electron configuration of sodium (Na)?

• 1s² 2s² 2p⁶ 3s¹

• 1s² 2s² 2p⁵

• 1s² 2s² 2p⁶ 3p¹

• 1s² 2s² 2p⁶ 3s²

Answer explanation

The electron configuration of sodium (Na) is 1s² 2s² 2p⁶ 3s¹. Sodium has 11 electrons, filling the first two energy levels completely and leaving one electron in the 3s subshell, which corresponds to the correct choice.

In the electronic configuration of an atom, how many electrons can the d-subshell hold?

• 2

• 6

• 10

• 14

Answer explanation

The d-subshell can hold a maximum of 10 electrons. This is because it consists of 5 orbitals, and each orbital can hold 2 electrons, leading to a total of 5 x 2 = 10 electrons.

Which of the following is the correct electron configuration for chlorine (Cl)?

• 1s² 2s² 2p⁶ 3s² 3p⁵

• 1s² 2s² 2p⁵ 3s² 3p⁵

• 1s² 2s² 2p⁶ 3s² 3p⁶

• 1s² 2s² 2p⁵ 3s¹ 3p⁶

Answer explanation

The correct electron configuration for chlorine (Cl), which has 17 electrons, is 1s² 2s² 2p⁶ 3s² 3p⁵. This configuration shows that chlorine has 7 valence electrons, consistent with its position in group 17 of the periodic table.

What is the electron configuration of an iron (Fe) atom (atomic number 26)?

• [Ar] 3d⁶ 4s²

• [Ar] 3d⁶ 4s²

• [Ar] 3d⁷ 4s¹

• [Ne] 3d⁶ 4s²

Answer explanation

The electron configuration of iron (Fe) with atomic number 26 is [Ar] 3d⁶ 4s². This indicates that after filling the argon core, iron has 6 electrons in the 3d subshell and 2 in the 4s subshell, making the first two choices correct.

According to Hund’s Rule, how do electrons fill orbitals of the same subshell?

• A. Pair up before filling new orbitals

• B. Fill each orbital singly with parallel spins before pairing

• C. Fill randomly

• D. Fill highest energy orbitals first

Answer explanation

According to Hund's Rule, electrons fill orbitals of the same subshell by first occupying each orbital singly with parallel spins before pairing. This minimizes electron-electron repulsion, making option B the correct choice.

What is the electron configuration of sulfur (S), atomic number 16?

• 1s² 2s² 2p⁶ 3s² 3p⁴

• 1s² 2s² 2p⁶ 3s² 3p⁵

• 1s² 2s² 2p⁶ 3s² 3p²

• 1s² 2s² 2p⁶ 3s² 3p⁶

Answer explanation

Sulfur (S) has an atomic number of 16, meaning it has 16 electrons. The correct electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁴, which accounts for all 16 electrons, filling the orbitals in the correct order.

How many unpaired electrons are there in the ground state electron configuration of nitrogen (N, atomic number 7)?

• A. 1

• B. 2

• C. 3

• D. 4

Answer explanation

Nitrogen has an atomic number of 7, with the ground state electron configuration of 1s² 2s² 2p³. The 2p subshell has 3 electrons, resulting in 3 unpaired electrons. Therefore, the correct answer is A. 1.

Which of the following elements has the electron configuration [Ne] 3s² 3p²?

• Silicon (Si)

• Magnesium (Mg)

• Sulfur (S)

• Phosphorus (P)

Answer explanation

The electron configuration [Ne] 3s² 3p² corresponds to Silicon (Si), which has 14 electrons in total. The other options do not match this configuration: Mg has 12, S has 16, and P has 15 electrons.