Electrons, Energy Levels & Atomic Orbitals

The first energy level is divided into _______

• the 1s sub-level only

• the 1s and 1p sub-levels

• the 1s, 1p and 1d sub-levels

• the 1s, 1p, 1d and 1f sub-levels

Answer explanation

The first energy level is divided into 1s sub-level only.

Which principle states that electrons fill the lowest energy orbitals first?

• Hund's rule

• Lewis Dot Principle

• Aufbau Principle

• Pauli Exclusion Principle

Answer explanation

The Aufbau Principle explains that electrons occupy lower-energy orbitals before filling higher-energy ones. This systematic filling is essential for determining the electron configuration of an atom.

Pauli exclusion principle states that no two electrons can have the same set of four quantum numbers

• TRUE

• FALSE

Answer explanation

Pauli exclusion principle states that no two electrons can have the same set of four quantum numbers.

According to Hund's rule, how should electrons be distributed in degenerate orbitals?

• Electrons occupy separate orbitals with parallel spins

• Electrons fill orbitals with alternating spins immediately

• Electrons completely fill one orbital before moving to the next

• Electrons pair up in the lowest energy orbital first

Answer explanation

Hund's Rule states that electrons occupy degenerate orbitals singly with parallel spins to minimize repulsion. This arrangement lowers the energy and increases the stability of the atom.

What atom matches this electron configuration?
1s²2s²2p⁶3s²

• Sodium

• Calcium

• Magnesium

• Aluminium

Answer explanation

The electron configuration 1s²2s²2p⁶3s² corresponds to magnesium having 12 electrons in total.

Which electronic configuration correctly represents the ground state of chromium, accounting for its anomalous electronic configuration?

• A. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁴

• B. 1s² 2s² 2p⁶ 3s² 3p⁵ 4s¹ 3d⁵

• C. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

• D. 1s² 2s² 2p⁶ 3s² 3p³ 4s¹ 3d⁵

Answer explanation

C. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

Chromium exhibits an anomalous electron configuration to achieve extra stability with a half-filled d subshell.

Which electronic configuration correctly represents the ground state of copper?

• A. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁹

• B. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

• C. 1s² 2s² 2p⁶ 3s² 3p⁵ 4s² 3d¹⁰

• D. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

Answer explanation

B. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

Copper has an anomalous electron configuration that maximizes stability by having a fully filled d subshell.

Which of the following is a d block element?

• Sodium

• Iron

• Aluminium

• Argon

Answer explanation

B. Iron

D-block elements, also known as transition metals, are located in groups 3 to 12 of the periodic table. They are characterized by the filling of d orbitals.

The image shows the shape of a p orbital.

• TRUE

• FALSE

Answer explanation

FALSE.

A is spherical and shows an s orbital whereas B shows a p orbital with two lobes.

Which of the following represents the electronic configuration of a noble gas?

• 
• 
• 
• 

Answer explanation

Neon is a noble gas having atomic number 10 and hence a stable electronic configuration 2,8.