What is the Aufbau Principle?

The Aufbau Principle states that electrons fill the lowest energy orbitals first before occupying higher energy levels.

How is the electronic configuration of transition metals different?

Transition metals have partially filled d orbitals, and their electron configurations can be more complex. For example, iron (Fe, atomic number 26) has the configuration [Ar] 3d⁶ 4s².

How do you write the electronic configuration for ions?

For cations (positively charged ions), remove electrons from the highest energy orbitals first. For anions (negatively charged ions), add electrons to the lowest available orbitals. For example, the configuration of Cl⁻ (chloride ion) is [Ne] 3s² 3p⁶.

What is the role of Hund's Rule in electron configuration?

Hund's Rule states that electrons will fill degenerate orbitals singly before pairing up, ensuring the maximum number of unpaired electrons.

Electron Configuration: Rules to Write Electron Configuration

Electron Configuration of Elements: Get here the short notes on electron configuration and learn the rules to write electron configurations of the first 20 elements.

ByAtul Rawal

Jul 23, 2024, 17:30 IST

Know here Rules to Write Electron Configuration

s p d f Orbitals Electron configuration: Writing electron configurations is an important topic in chemistry. Students struggle to understand and write them during an exam. Here are some rules that you might have come across while studying this topic. Let us discuss the topic in more detail.

What is Electronic Configuration?

Electronic configuration is the arrangement of electrons in an atom's orbitals. It indicates how electrons are distributed among different energy levels and sublevels around the nucleus of an atom. Understanding electronic configuration helps predict an element's chemical properties, reactivity, and the type of bonds it can form.

Read: Atoms and Molecules: Definition, Size, And Examples

Example of Electronic Configuration

Consider the element oxygen, which has an atomic number of 8. This means it has 8 electrons. The electronic configuration of oxygen is written as follows:

The first two electrons fill the 1s orbital: 1s²
The next two electrons fill the 2s orbital: 2s²
The remaining four electrons go into the 2p orbitals: 2p⁴

So, the full electronic configuration for oxygen is:

Oxygen (O): 1s² 2s² 2p⁴

This notation shows that oxygen has 2 electrons in the first energy level (1s) and 6 electrons in the second energy level (2s and 2p).

Rules to Write Electron Configurations

The electronic configuration of an atom is written by distributing its electrons among the orbitals according to specific rules. The main rules are the Aufbau Principle, Pauli Exclusion Principle, and Hund's Rule.

Aufbau Principle: Electrons fill the lowest energy orbitals first before moving to higher energy levels.
Pauli Exclusion Principle: An orbital can hold a maximum of two electrons with opposite spins.
Hund's Rule: Electrons will fill degenerate orbitals (orbitals with the same energy) singly before pairing up.

How to Fill Atomic Orbitals?

Atomic orbitals are filled in a specific order based on their energy levels. The order can be remembered using the following sequence:

1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p

For example, the electron configuration of hydrogen (atomic number 1) is 1s¹. For helium (atomic number 2), it is 1s². For lithium (atomic number 3), it is 1s² 2s¹.

Representation of Electronic Configuration of Atom

The electronic configuration can be represented using the following notation:

Spectroscopic Notation: Shows the distribution of electrons in each orbital. For example, the electronic configuration of carbon (atomic number 6) is written as 1s² 2s² 2p².
Orbital Box Diagram: Uses boxes to represent orbitals and arrows to represent electrons. For example, the configuration of nitrogen (atomic number 7) is:

1s: ↑↓

2s: ↑↓

2p: ↑ ↑ ↑

Noble Gas Notation: Uses the previous noble gas to simplify the notation. For example, the configuration of sodium (atomic number 11) can be written as [Ne] 3s¹.

Electronic Configuration of First 20 Elements

Check and note down the electronic configuration of the first 20 elements of the periodic table.

Atomic Number	Element (Symbol)	Electronic Configuration
1	Hydrogen (H)	1s¹
2	Helium (He)	1s²
3	Lithium (Li)	[He]²s¹
4	Beryllium (Be)	[He]²s²
5	Boron (B)	[He]²s²²p¹
6	Carbon (C)	[He]²s²²p²
7	Nitrogen (N)	[He]²s²²p³
8	Oxygen (O)	[He]²s²²p⁴
9	Fluorine (F)	[He]²s²²p⁵
10	Neon (Ne)	[He]²s²²p⁶
11	Sodium (Na)	[Ne]³s¹
12	Magnesium (Mg)	[Ne]³s²
13	Aluminum (Al)	[Ne]³s²³p¹
14	Silicon (Si)	[Ne]³s²³p²
15	Phosphorus (P)	[Ne]³s²³p³
16	Sulfur (S)	[Ne]³s²³p⁴
17	Chlorine (Cl)	[Ne]³s²³p⁵
18	Argon (Ar)	[Ne]³s²³p⁶
19	Potassium (K)	[Ar]⁴s¹
20	Calcium (Ca)	[Ar]⁴s²