The Electron Configuration Review: Videos & Practice Problems

Understanding electron configurations is essential for grasping how electrons are distributed among orbitals in an atom. Electrons fill orbitals starting from the lowest energy level, following the Aufbau principle, which dictates the sequence from 1s to 2s, then 2p, and so forth. The periodic table can be reimagined into blocks—s, p, d, and f—that correspond to the sublevels and their maximum electron capacities: s holds 2, p holds 6, d holds 10, and f holds 14 electrons. The position of elements within these blocks helps determine their electron configuration. For a more efficient approach, condensed electron configurations use the last noble gas as a reference point, simplifying the representation of electron arrangements. This method is preferred unless a full ground state electron configuration is specifically requested. Understanding these concepts is crucial for predicting chemical properties and behaviors of elements.

Ground State Electron Configurations

Understanding electron configuration is essential for grasping how electrons are distributed in an atom. The Aufbau principle guides this process, stating that electrons fill orbitals starting from the lowest energy level to the highest. This means we begin with the 1s orbital, followed by 2s, 2p, and so forth, ensuring that lower energy orbitals are filled before higher ones.

To visualize this filling order, the Aufbau diagram is a helpful tool. It illustrates the sequence in which orbitals are filled: starting from 1s, we progress to 2s, then 2p, 3s, 3p, 4s, and continue this pattern through 3d, 4p, 5s, and up to 8s. The diagram also includes the transition through 3d to 6d and 4f to 5f orbitals, providing a comprehensive view of the electron filling process.

Another effective method for determining electron configurations is by utilizing the periodic table. Each element's position on the table corresponds to its electron configuration, allowing for a more intuitive understanding of how electrons are arranged in various elements and ions. This approach not only simplifies the process but also reinforces the connection between an element's properties and its electron configuration.

Auf Bau Principle

The periodic table can be visualized in a structured way, divided into distinct blocks that represent different electron sublevels. These blocks are categorized as the s block (blue), p block (yellow), d block (purple), and f block (red). Each block corresponds to specific orbital configurations and maximum electron capacities. The s block contains 1 orbital, allowing for a maximum of 2 electrons, which is why it consists of 2 columns. The p block has 3 orbitals, accommodating up to 6 electrons, hence its 6 slots. The d block, with 5 orbitals, can hold up to 10 electrons, while the f block, featuring 7 orbitals, can contain a maximum of 14 electrons.

Starting with hydrogen, the electron configuration begins as \(1s^1\). As we progress through the periodic table, we incrementally add electrons. For example, helium is represented as \(1s^2\). In the second row, the configurations continue with \(2s^1\) for lithium and \(2s^2, 2p^1\) for boron, following the pattern of filling the s and p blocks. The d block configurations drop down by one principal energy level; thus, the first d block element, scandium, is represented as \(3d^1\) after filling \(4s^2\).

For the f block, the same principle applies, where the configurations also drop down by one number. For instance, the first f block element, lanthanum, is represented as \(4f^1\) after filling \(6s^2\). This structured approach allows for a clear understanding of how to determine the electron configuration for any element or ion by following the periodic table's layout.

The Electron Configuration Example

To determine the ground state electron configuration of fluorine, which has an atomic number of 9, we start by recognizing that this means fluorine has 9 electrons. The electron configuration describes how these electrons are distributed among the various atomic orbitals.

We begin with the lowest energy level, which is the 1s orbital. The filling order of the orbitals follows the Aufbau principle, where electrons occupy the lowest energy orbitals first. For fluorine, the electron configuration proceeds as follows:

1. The 1s orbital can hold a maximum of 2 electrons, so we write 1s².

2. Next, we fill the 2s orbital, which also holds 2 electrons: 2s².

3. Finally, we move to the 2p orbital. Fluorine has 5 electrons in this orbital, which we denote as 2p⁵.

Putting it all together, the ground state electron configuration for fluorine is:

1s² 2s² 2p⁵.

When we add the electrons from each orbital (2 from 1s, 2 from 2s, and 5 from 2p), we confirm that the total is 9 electrons, consistent with the atomic number of fluorine. This relationship highlights that in a neutral atom, the atomic number indicates both the number of protons and electrons, ensuring charge neutrality.

Utilizing the periodic table effectively can guide you in determining the electron configurations for any element or ion, making it a valuable tool in understanding atomic structure.

Which electron configuration represents a violation of the Auf Bau Principle? 

• A.
• B.
• C.
• D.

Answer: (B)

Identify the element with the given electron orbital diagram. 

• A. Silicon
• B. Fluorine
• C. Sulfur
• D. Chlorine
• E. Phosphorus

Answer: (C)

Write the electron configuration and electron orbital diagram for the following element: 
Mn (Z = 25) 

• A. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵
• B. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4d⁵
• C. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁴
• D. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵

Answer: (D)

Write the ground-state electron configuration for the following element: 
Lead (Z = 82) 

• A. $1s^22s^22p^63s^23p^64s^23d^{10}4p^65s^24d^{10}5p^66s^24f^{10}5d^{10}6p^6$
• B. $1s^22s^22p^63s^23p^64s^23d^{10}4p^65s^24d^{10}5p^66s^24f^{14}6p^2$
• C. $1s^22s^22p^63s^23p^64s^23d^{10}4p^65s^24d^{10}5p^66s^24f^{14}5d^66p^6$
• D. $1s^22s^22p^63s^23p^64s^23d^{10}4p^65s^24d^{10}5p^66s^24f^{14}5d^{10}6p^2$

Answer: (D)

Condensed Electron Configuration

Condensed electron configurations provide a streamlined method for representing the electron arrangements of elements and ions. This approach begins with the last noble gas preceding the element in question, allowing for a more efficient notation. Understanding the layout of the periodic table is crucial, as it is divided into blocks: the s block starts with 1s, followed by the p block, d block, and f block.

When tasked with determining the condensed electron configuration, it is essential to identify the specific element and the noble gas that comes before it. In most cases, unless specified otherwise, the condensed form is the preferred method for writing electron configurations, rather than the full ground state configuration. This technique not only simplifies the representation but also highlights the core electrons, which are the electrons in the inner shells, while focusing on the valence electrons that are involved in chemical bonding.

By mastering condensed electron configurations, students can enhance their understanding of electron arrangements and their implications in chemical behavior, making it a vital skill in the study of chemistry.

The Electron Configuration: Condensed Example

To determine the condensed electron configuration for an aluminum atom, which is neutral and has an atomic number of 13, we follow a systematic approach. First, we identify aluminum on the periodic table, confirming it has 13 electrons.

Next, we locate the nearest noble gas preceding aluminum, which is neon (Ne). We place neon in brackets to represent the electron configuration of the filled inner shells. This step simplifies our notation significantly.

Continuing from neon, we complete the electron configuration for aluminum. After neon, the next electrons fill the 3s and 3p orbitals. Thus, the configuration becomes:

[Ne] 3s^2 3p^1

This condensed electron configuration effectively replaces the longer form of writing out all the filled orbitals, which would be 1s^2 2s^2 2p^6 3s^2 3p^1. By using the condensed form, we save time and effort while accurately representing the electron arrangement of aluminum.

Write the condensed electron configuration and electron orbital diagram for the following element: Zinc 

• A. [Ar] 4s² 3d⁹
• B. [Kr] 4s² 3d¹⁰
• C. [Ar] 4s² 3d¹⁰
• D. [Ar] 4s¹ 3d¹⁰

Answer: (C)

Here’s what students ask on this topic:

What is the Aufbau principle in electron configuration?

The Aufbau principle is a fundamental concept in electron configuration that states electrons fill orbitals starting from the lowest energy level before moving to higher energy levels. This principle helps determine the order in which electrons are added to the orbitals. The sequence begins with the 1s orbital, followed by 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on. The principle ensures that electrons occupy the most stable (lowest energy) configuration possible. This is crucial for understanding the distribution of electrons in atoms and predicting their chemical properties.

How do you use the periodic table to determine electron configurations?

The periodic table can be reimagined into blocks—s, p, d, and f—that correspond to the sublevels and their maximum electron capacities: s holds 2, p holds 6, d holds 10, and f holds 14 electrons. The position of elements within these blocks helps determine their electron configuration. For example, elements in the s-block have their outermost electrons in s orbitals, while those in the p-block have their outermost electrons in p orbitals. By following the order of the blocks and their respective rows, you can determine the electron configuration of any element or ion.

What is a condensed electron configuration?

A condensed electron configuration is a shorthand method of writing electron configurations that starts at the last noble gas before the desired element. This method simplifies the representation of electron arrangements by using the noble gas as a reference point. For example, the condensed electron configuration for sodium (Na) is [Ne] 3s¹, where [Ne] represents the electron configuration of neon, the noble gas preceding sodium. This approach is preferred unless a full ground state electron configuration is specifically requested.

What are the maximum electron capacities of the s, p, d, and f sublevels?

The maximum electron capacities of the sublevels are as follows: the s sublevel can hold up to 2 electrons, the p sublevel can hold up to 6 electrons, the d sublevel can hold up to 10 electrons, and the f sublevel can hold up to 14 electrons. These capacities are determined by the number of orbitals in each sublevel, with each orbital capable of holding 2 electrons. Understanding these capacities is essential for determining the electron configurations of elements.

Why is understanding electron configurations important in chemistry?

Understanding electron configurations is crucial in chemistry because it helps predict the chemical properties and behaviors of elements. Electron configurations determine how atoms interact with each other, form bonds, and participate in chemical reactions. By knowing the distribution of electrons among orbitals, chemists can explain the reactivity, stability, and other characteristics of elements and compounds. This knowledge is fundamental for studying and applying various chemical principles and processes.