Understanding Electron Configurations

What is the electron configuration of a neutral oxygen atom?

Answer explanation

A neutral oxygen atom has 8 electrons. The electron configuration fills the 1s and 2s orbitals first, followed by 4 electrons in the 2p orbital, resulting in 1s² 2s² 2p⁴, which is the correct choice.

Which of the following is the correct electron configuration for carbon?

Answer explanation

The correct electron configuration for carbon, which has 6 electrons, is 1s² 2s² 2p². This configuration fills the 1s and 2s orbitals completely and places 2 electrons in the 2p orbital.

What is the noble gas configuration for sodium (Na)?

Answer explanation

Sodium (Na) has an atomic number of 11. Its electron configuration is 1s² 2s² 2p⁶ 3s¹. The noble gas configuration uses the nearest noble gas, neon (Ne), resulting in [Ne] 3s¹ as the correct answer.

How many valence electrons does chlorine have?

• 5

• 6

• 7

• 8

Answer explanation

Chlorine has 7 valence electrons, which are found in its outermost shell. This is determined by its position in the periodic table, specifically in group 17 (halogens), where elements typically have 7 valence electrons.

• Bromine (Br)

• Krypton (Kr)

• Selenium (Se)

• Arsenic (As)

Answer explanation

The electron configuration [Ar]4s^23d^{10}4p^5 corresponds to the element with atomic number 35, which is Bromine (Br). The other options do not match this configuration.

What is the electron configuration for the transition metal iron (Fe)?

Answer explanation

The electron configuration for iron (Fe), which has an atomic number of 26, is [Ar]4s²3d⁶. This indicates that there are 2 electrons in the 4s subshell and 6 electrons in the 3d subshell, making the first choice correct.

Which rule states that electrons fill orbitals starting with the lowest energy level first?

• Hund's Rule

• Pauli Exclusion Principle

• Aufbau Principle

• Heisenberg Uncertainty Principle

Answer explanation

The Aufbau Principle states that electrons occupy the lowest energy orbitals first before filling higher ones. This principle helps explain the electron configuration of atoms.

What is the electron configuration of a neutral sulfur atom?

Answer explanation

A neutral sulfur atom has 16 electrons. The correct electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁴, which accounts for all 16 electrons, with 4 in the 3p subshell. The other options either exceed or do not match the total electron count.

Which of the following is the correct noble gas configuration for calcium (Ca)?

Answer explanation

The correct noble gas configuration for calcium (Ca) is [Ar] 4s². Calcium has 20 electrons, and after the noble gas argon (Ar), it has two additional electrons in the 4s subshell.

How many unpaired electrons are present in the ground state of a nitrogen atom?

• 1

• 2

• 3

• 4

Answer explanation

A nitrogen atom has 7 electrons. In its ground state, the electron configuration is 1s² 2s² 2p³. The 2p subshell has 3 unpaired electrons, making the correct answer 3.