•

Updated Apr 6, 2026

•

7 pages

Understanding Ionization Energies and Atomic Structure

Alexia C. Tario

@kikki_05

Understanding atomic structure is crucial for mastering chemistry - it's... Show more

1 / 7

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Atomic Structure Basics

Every atom is made up of three fundamental particles that determine its identity and behaviour. The nucleus contains protons $charge +1, mass 1$ and neutrons (charge 0, mass 1), whilst electrons $charge -1, mass 0$ orbit around it.

Your atomic number tells you exactly how many protons and electrons an atom has - they're always equal in a neutral atom. The atomic mass is simply the total number of protons plus neutrons, which gives you the atom's weight.

Isotopes are atoms of the same element that have different numbers of neutrons but identical numbers of protons and electrons. For example, carbon can exist as ¹²C, ¹³C, and ¹⁴C - all with 6 protons but 6, 7, or 8 neutrons respectively. Since chemical properties depend on electrons, all isotopes of an element behave identically in reactions.

Quick Tip: Remember that atomic number = protons = electrons, whilst atomic mass = protons + neutrons.

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Relative Atomic Mass and Mass Spectrometry

Relative atomic mass (Ar) isn't just a simple average - it's a weighted average that accounts for how common each isotope is in nature. The formula is: Ar = Σ(% abundance × isotopic mass) ÷ Σ(% abundance).

Let's see this in action with copper. Cu-63 makes up 69.2% of natural copper, whilst Cu-65 accounts for 30.8%. Using the formula: Ar = [(69.2 × 63) + (30.8 × 65)] ÷ 100 = 63.6.

Mass spectrometry is the technique scientists use to identify these isotopes and their abundances. The process involves four key steps: ionisation (creating charged particles), acceleration (speeding them up), ion drift (separating by mass), and detection (measuring the results).

Real World: Mass spectrometry is used in everything from drug testing to space exploration!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Electron Shells and Orbitals

Electrons don't just randomly orbit the nucleus - they occupy specific energy levels called shells. Think of these like the floors of a building, where each floor can only hold a certain number of residents.

The maximum number of electrons in each shell follows the 2n² rule, where n is the shell number. Shell 1 holds 2 electrons, shell 2 holds 8, shell 3 holds 18, and shell 4 holds 32 electrons maximum.

Within each shell, electrons occupy sub-shells (s, p, d, f) that have different shapes and capacities. The s sub-shell holds 2 electrons, p holds 6, d holds 10, and f holds 14. Shell 1 only has s, shell 2 has s and p, shell 3 has s, p, and d, whilst shell 4 contains all four types.

Memory Trick: The sub-shell capacities (2, 6, 10, 14) follow the pattern of adding 4 each time!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Orbital Shapes and Electron Configuration

Orbitals have distinct shapes that determine where you're likely to find electrons. The s orbital is spherical, whilst p orbitals are dumbbell-shaped and come in three orientations (px, py, pz) pointing along different axes.

When writing electron configurations, you fill orbitals starting from the lowest energy level. For example, carbon (6 electrons) has the configuration 1s² 2s² 2p², showing exactly where each electron resides.

The filling pattern follows a specific order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on. Notice that 4s fills before 3d because it's actually at a lower energy level despite being in the "fourth shell".

Study Tip: Draw out the orbital filling diagram - visual learners find this much easier than memorising the sequence!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Advanced Electron Configuration Rules

Pauli's Exclusion Principle states that each orbital can hold a maximum of two electrons, and they must have opposite spins (represented as ↑↓). This prevents electrons from occupying the same space with identical properties.

When electrons enter orbitals of equal energy (like the three p orbitals), they prefer to occupy separate orbitals first before pairing up. This Hund's rule minimises electron repulsion and creates more stable atoms.

Shorthand notation makes writing electron configurations much quicker. Instead of writing out every orbital, you can use the nearest noble gas in brackets. For example, calcium (20 electrons) becomes [Ar] 4s² rather than the full 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².

Exam Tip: Learn the electron configurations of the first 20 elements - they appear in most chemistry exams!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Ionisation Energy Fundamentals

Ionisation energy is the energy needed to remove one mole of electrons from one mole of gaseous atoms, creating positive ions. It's measured in kJ/mol and tells you how tightly an atom holds onto its electrons.

The process can happen multiple times: first ionisation energy removes the first electron $X → X⁺ + e⁻$ , second ionisation energy removes the second $X⁺ → X²⁺ + e⁻$ , and so on. Each successive ionisation requires more energy because you're removing electrons from increasingly positive ions.

Down a group, ionisation energy decreases dramatically. As you move from lithium to sodium to potassium, the atoms get larger and the outer electrons become further from the nucleus. This weaker nuclear attraction makes electrons easier to remove.

Key Insight: Ionisation energy patterns help explain why metals lose electrons easily whilst non-metals prefer to gain them!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Ionisation Energy Trends

Across a period, ionisation energy generally increases from left to right. As you move from lithium to neon, the nuclear charge increases whilst the atomic radius decreases slightly, creating a stronger pull on the electrons.

However, there are important exceptions to this trend. Boron has a lower ionisation energy than beryllium because its electron is in a higher energy p orbital. Similarly, oxygen's ionisation energy is slightly lower than nitrogen's due to electron repulsion in paired orbitals.

These periodic trends in ionisation energy help predict chemical behaviour. Elements with low ionisation energies (like sodium) readily form positive ions, whilst those with high ionisation energies (like fluorine) prefer to gain electrons instead.

Exam Focus: Learn the exceptions to the general trend - examiners love testing these anomalies!

We thought you’d never ask...

What is the Knowunity AI companion?

Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.

Where can I download the Knowunity app?

You can download the app from Google Play Store and Apple App Store.

Is Knowunity really free of charge?

That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.

Most popular content in Chemistry

GCSE AQA Chemistry Topic 1

Quiz covering all of topic 1

Chemistry

Quick Runthrough of Chemistry Paper 1

FOR FT HT COMBINED & HIGHER

Chemistry

GCSE Chemistry Revision Notes

AQA GCSE Combined Chemistry * detailed summary

Chemistry

A-level OCR A Chemistry summary sheets

Everything from snaprevise for OCR chemistry a-level

Chemistry

Essential Chemistry Practicals

Explore key AQA GCSE Chemistry practicals, including flame tests, titration, and gas identification. This resource covers essential techniques for analyzing ions, making salts, and understanding reaction kinetics. Perfect for students preparing for exams and practical assessments.

Chemistry

AQA GCSE Chemistry 4.2 Bonding, structure and the Properties of Matter

4.2 Metals and Alloys

Chemistry

chem paper 1

higher

Chemistry

Redox Reactions Overview

Explore the fundamentals of redox reactions, including oxidation states, definitions of oxidation and reduction, and the roles of oxidizing and reducing agents. This summary covers key rules for determining oxidation states, the concept of disproportionation, and practical applications in chemical equations. Ideal for A-Level Chemistry students preparing for exams.

Chemistry

AQA GCSE Biology 4.1 Atomic structure and the Periodic Table

4.1 Mixtures

Chemistry

Most popular content

Sociology of Education Overview

Explore comprehensive A-Level Sociology notes on the education system, covering key theories, policies, and sociological perspectives. This resource includes insights on marketisation, gender roles, cultural deprivation, and educational inequalities, providing a thorough understanding of how education shapes social stratification and individual achievement. Ideal for exam preparation and in-depth study.

Sociology

An Inspector Calls: Character Insights

Explore in-depth analysis and key quotes for characters in J.B. Priestley's 'An Inspector Calls'. This resource covers Gerald Croft, Inspector Goole, Sheila Birling, Mrs. Birling, Eric Birling, and Eva Smith, focusing on themes of class, gender roles, and social responsibility. Ideal for students aiming for Grade 8 and above.

English Literature

Comprehensive Crime & Deviance Overview

Explore an extensive revision of crime and deviance topics, including theories, types of crime, and the impact of media. This resource covers key concepts such as Marxism, functionalism, gender and crime, and the influence of globalization on criminal behavior. Ideal for students seeking a thorough understanding of criminology and its various theories. Type: Full Topic Revision.

Sociology

Sociology of Families: Comprehensive Revision

Dive into an extensive overview of family dynamics, perspectives, and patterns in sociology. This resource covers key concepts such as family diversity, gender roles, marriage, and the impact of social policies on family structures. Perfect for A-Level Sociology students preparing for Paper 2.

Sociology

WJEC Unit 4 Criminology

Criminology unit 4 detailed revision note

Criminology

aqa higher tier combined science - biology b1 : cell biology, paper 1

b1: cell biology - paper 1

Biology

Criminology: Crime & Punishment Overview

Comprehensive mindmaps covering key concepts in the Crime and Punishment topic for WJEC Criminology Unit 4. This resource includes detailed insights into the Criminal Justice System, crime prevention strategies, sentencing models, and the roles of various agencies. Ideal for A-Level revision, ensuring you grasp essential theories and legislative processes to excel in your exams.

Criminology

Macbeth: Guilt and Ambition

Explore the complex themes of guilt and ambition in Shakespeare's 'Macbeth'. This analysis covers key characters, including Macbeth and Lady Macbeth, their moral dilemmas, and the tragic consequences of their ambition. Ideal for students studying character motivations, thematic elements, and the psychological impact of power. Includes insights on the natural order, manipulation, and the descent into madness.

English Literature

AQA Biology: Key Concepts

Explore essential AQA Biology topics including Photosynthesis, Respiration, Homeostasis, Genetics, and Ecology. This comprehensive knowledge organizer covers key concepts such as energy transfer, hormonal control, and genetic variation, providing a solid foundation for your studies. Ideal for exam preparation and understanding biological processes.

Biology

Can't find what you're looking for? Explore other subjects.

Students love us — and so will you.

4.6/5

App Store

4.7/5

Google Play

The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.

Stefan S

iOS user

This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.

Samantha Klich

Android user

Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.

Anna

iOS user

Best app on earth! no words because it’s too good

Thomas R

iOS user

Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.

Basil

Android user

This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.

David K

iOS user

The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!

Sudenaz Ocak

Android user

In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.

Greenlight Bonnie

Android user

very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.

Rohan U

Android user

I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.

Xander S

iOS user

THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮

Elisha

iOS user

This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now

Paul T

iOS user

Stefan S

iOS user

Samantha Klich

Android user

Anna

iOS user

Best app on earth! no words because it’s too good

Thomas R

iOS user

Basil

Android user

David K

iOS user

Sudenaz Ocak

Android user

In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.

Greenlight Bonnie

Android user

Rohan U

Android user

Xander S

iOS user

Elisha

iOS user

Paul T

iOS user

Chemistry

•

Updated Apr 6, 2026

•

7 pages

Understanding Ionization Energies and Atomic Structure

Alexia C. Tario

@kikki_05

Understanding atomic structure is crucial for mastering chemistry - it's the foundation that explains how elements behave and react. You'll explore everything from the basic parts of an atom to electron configurations and ionisation energy trends.

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

Atomic Structure Basics

Quick Tip: Remember that atomic number = protons = electrons, whilst atomic mass = protons + neutrons.

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

Relative Atomic Mass and Mass Spectrometry

Let's see this in action with copper. Cu-63 makes up 69.2% of natural copper, whilst Cu-65 accounts for 30.8%. Using the formula: Ar = [(69.2 × 63) + (30.8 × 65)] ÷ 100 = 63.6.

Real World: Mass spectrometry is used in everything from drug testing to space exploration!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

Electron Shells and Orbitals

Memory Trick: The sub-shell capacities (2, 6, 10, 14) follow the pattern of adding 4 each time!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

Orbital Shapes and Electron Configuration

Study Tip: Draw out the orbital filling diagram - visual learners find this much easier than memorising the sequence!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

Advanced Electron Configuration Rules

Exam Tip: Learn the electron configurations of the first 20 elements - they appear in most chemistry exams!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

Ionisation Energy Fundamentals

Key Insight: Ionisation energy patterns help explain why metals lose electrons easily whilst non-metals prefer to gain them!

$Charge Mass Prime Tuition Nucleus $\rightarrow$ Protons +1 1 $\rightarrow$ Neutrons 0 1 $\rightarrow$ Electrons -1 0 $A_R$ = Relative atom$

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

Ionisation Energy Trends

Exam Focus: Learn the exceptions to the general trend - examiners love testing these anomalies!