What is the difference between an electron's 'ground state' and an 'excited state'?

The ground state is the original, lowest-energy level an electron occupies. An excited state occurs when an electron absorbs energy and moves to a higher energy level further from the nucleus.

How does the process of electron absorption differ from emission?

Absorption involves an electron taking in electromagnetic radiation to move to a higher shell. Emission is the release of that energy as radiation when the electron falls back to a lower shell closer to the nucleus.

What is the distinction between an atom and a positive ion in terms of electron count?

An atom is neutral because its electron count equals its proton count. A positive ion has lost one or more electrons, resulting in more positive protons than negative electrons.

What error occurs if you include electrons when calculating an atom's mass number?

The mass number would be technically incorrect because electrons have negligible mass (approx. $1/2000$ of a proton). The mass number is defined strictly as the sum of protons and neutrons in the nucleus.

Why is it incorrect to say an atom becomes a positive ion by gaining protons?

Gaining protons would change the identity of the element itself (changing the atomic number). Ionization only involves the loss or gain of electrons, which changes the charge without changing the element.

What happens if you fill the second energy level before the first is full?

This violates the principle of minimum energy, where electrons naturally occupy the lowest available energy state. In a stable atom, the first shell must contain $2$ electrons before the second shell begins to fill.

Define an 'Energy Level' in the context of atomic structure.

An energy level is a specific, quantized region at a fixed distance from the nucleus where electrons orbit. Each level can only hold a specific maximum number of electrons.

What is a 'Positive Ion'?

A positive ion is an atom that has lost one or more electrons, giving it an overall positive charge because the number of protons exceeds the number of electrons.

What is the maximum electron capacity for the first three energy levels?

The first energy level can hold a maximum of $2$ electrons, the second can hold $8$, and the third can also hold $8$.

How is the total charge of an atom calculated?

Total charge is the sum of the positive charges (protons) and negative charges (electrons). In a neutral atom, $(+n) + (-n) = 0$.

Electron Structure | Pearson Edexcel GCSE Physics

Electron Structure

Summary

Electron structure describes the arrangement of electrons in an atom, specifically how they occupy distinct energy levels at varying distances from the nucleus. This configuration determines an atom's stability, its interaction with electromagnetic radiation, and its ability to form ions through the loss of outer-shell electrons.

1. Definition & Core Concepts

Electrons are negatively charged subatomic particles that orbit the nucleus of an atom within specific regions known as energy levels or electron shells.

Each energy level exists at a fixed distance from the nucleus, and the arrangement of electrons across these levels defines the atom's electronic configuration.

In a neutral atom, the total number of electrons is exactly equal to the number of protons in the nucleus, ensuring the overall electrical charge is zero.

Diagram of an atom showing a central nucleus surrounded by concentric dashed lines representing energy levels, with blue electrons orbiting and an orange arrow indicating an electron moving to a higher shell.

2. Underlying Principles of Energy Levels

Energy levels are quantized, meaning electrons can only exist at specific distances from the nucleus and cannot reside in the spaces between these shells.

The energy of an electron is directly related to its distance from the nucleus; electrons in shells further away possess higher potential energy.

This energy relationship is analogous to a ladder, where moving an electron to a higher shell requires an input of energy to overcome the electrostatic attraction of the positive nucleus.

3. Methods & Techniques: Shell Capacity

4. Key Distinctions: Absorption vs. Emission

Process	Direction	Energy Change	Result
Absorption	Moves to a shell further from nucleus	Absorbs EM radiation (light/heat)	Atom enters an 'excited state'
Emission	Moves to a shell closer to nucleus	Releases EM radiation	Atom returns to 'ground state'

The specific colors of light observed in a spectrum are the result of electrons falling between specific energy levels and emitting photons of corresponding energy.

While absorption is a temporary state, emission is the process by which an atom sheds excess energy to regain stability.

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions