IB Chemistry Topic S3.1.2 Electron Configuration and Group Trends Revision Notes (SL/HL)

IB Chemistry Topic S3.1.2 Electron Configuration and Group Trends Revision Notes (SL/HL) | RevisionDojo

Written by official IB examiners

Understanding Electron Configuration and Periodic Table Patterns

What is Electron Configuration?

Definition

Electron configuration

Electron configuration refers to the arrangement of electrons in an atom’s energy levels, sublevels, and orbitals.

Electrons occupy regions around the nucleus called orbitals, which are grouped into sublevels (s, p, d, f) and energy levels (designated by principal quantum numbers, $n$).
Here’s the key rule: electrons fill orbitals in order of increasing energy, following the Aufbau principle.

Example

The $1s$ orbital is filled first, followed by $2s$, $2p$, $3s$, and so on.
Each orbital has a maximum electron capacity: $s$ holds 2, $p$ holds 6, $d$ holds 10, and $f$ holds 14.

Using the Periodic Table to Determine Electron Configuration

The block an element sits in tells you which sublevel its outermost electrons are filling: the s-block fills an s sublevel, the p-block a p sublevel, the d-block a d sublevel, and the f-block an f sublevel. The full block map is set out in S3.1.1.

Example question

Determine the electron configuration of phosphorus ($Z=15$).

Solution

Locate phosphorus in Group 15 and Period 3 of the periodic table.
Period 3 tells us the outermost electrons are in the $n=3$ energy level.
Group 15 indicates phosphorus has 5 valence electrons (electrons in the outermost energy level).
Fill the orbitals in order: $1s^2$, $2s^2$, $2p^6$ (inner electrons sum to 10, corresponding to neon’s configuration).
The remaining 5 electrons go into $3s^2$ and $3p^3$.
The full electron configuration is: $1s^2 2s^2 2p^6 3s^2 3p^3$.
The condensed configuration is: $[Ne] 3s^2 3p^3$.

Tip

Use the periodic table as a map: the period number tells you the principal energy level ($n$), while the block and group number guide you to the sublevel and number of valence electrons.

Group Numbers and Valence Electrons

What Do Group Numbers Tell Us?

Definition

Group number

The group number of an element indicates the number of valence electrons in its outermost energy level.

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Understanding Electron Configuration and Periodic Table Patterns

What is Electron Configuration?

Definition

Electron configuration

Electron configuration refers to the arrangement of electrons in an atom’s energy levels, sublevels, and orbitals.

Electrons occupy regions around the nucleus called orbitals, which are grouped into sublevels (s, p, d, f) and energy levels (designated by principal quantum numbers, $n$).
Here’s the key rule: electrons fill orbitals in order of increasing energy, following the Aufbau principle.

Example

The $1s$ orbital is filled first, followed by $2s$, $2p$, $3s$, and so on.
Each orbital has a maximum electron capacity: $s$ holds 2, $p$ holds 6, $d$ holds 10, and $f$ holds 14.

Using the Periodic Table to Determine Electron Configuration

Example question

Determine the electron configuration of phosphorus ($Z=15$).

Solution

Locate phosphorus in Group 15 and Period 3 of the periodic table.
Period 3 tells us the outermost electrons are in the $n=3$ energy level.
Group 15 indicates phosphorus has 5 valence electrons (electrons in the outermost energy level).
Fill the orbitals in order: $1s^2$, $2s^2$, $2p^6$ (inner electrons sum to 10, corresponding to neon’s configuration).
The remaining 5 electrons go into $3s^2$ and $3p^3$.
The full electron configuration is: $1s^2 2s^2 2p^6 3s^2 3p^3$.
The condensed configuration is: $[Ne] 3s^2 3p^3$.

Tip

Use the periodic table as a map: the period number tells you the principal energy level ($n$), while the block and group number guide you to the sublevel and number of valence electrons.

Group Numbers and Valence Electrons

What Do Group Numbers Tell Us?

Definition

Group number

The group number of an element indicates the number of valence electrons in its outermost energy level.

Definition

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry S3.1.2 Electron Configuration and Group Trends Notes

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

Understanding Electron Configuration and Periodic Table Patterns

What is Electron Configuration?

Using the Periodic Table to Determine Electron Configuration

Group Numbers and Valence Electrons

What Do Group Numbers Tell Us?

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Understanding Electron Configuration and Periodic Table Patterns

What is Electron Configuration?

Using the Periodic Table to Determine Electron Configuration

Group Numbers and Valence Electrons

What Do Group Numbers Tell Us?

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