•

Updated Apr 4, 2026

•

2 pages

Understanding Atomic and Mass Numbers, Isotopes, and Ions

RiceFarmer

@ricefarmer_jhrs

Ever wondered what makes each element unique on the periodic... Show more

Atomic and Mass Numbers

Understanding atoms is like cracking a secret code that's written right on the periodic table. Every element has two crucial numbers that tell you exactly what's happening inside its atoms.

The atomic number is the smaller number you'll see on each element. This number is absolutely vital because it tells you how many protons and electrons are in a normal atom of that element. For instance, lithium has an atomic number of 3, which means every lithium atom contains exactly 3 protons and 3 electrons.

The mass number is the larger number, and it reveals the total count of protons and neutrons combined. Since lithium's mass number is 7 and it has 3 protons, you can work out that it must have 4 neutrons. The simple trick is: neutrons = mass number - atomic number.

Isotopes are like different versions of the same element. They have identical numbers of protons and electrons, but different numbers of neutrons. This means isotopes of the same element behave chemically the same way, but have different masses.

Quick Check: Try finding the protons, neutrons, and electrons for magnesium (Mg), calcium (Ca), and potassium (K) using a periodic table!

Ions

Sometimes atoms don't play by the usual rules - they can gain or lose electrons and become charged particles called ions. This happens when atoms want to become more stable, and it's absolutely crucial for understanding how elements bond together.

Positive ions form when an atom loses one or more electrons. Since electrons carry negative charge, losing them leaves the atom with more positive protons than negative electrons, creating an overall positive charge.

Negative ions work the opposite way - they form when atoms gain extra electrons. Now there are more negatively charged electrons than positive protons, giving the ion an overall negative charge.

Remember, ions still keep the same number of protons (that never changes for an element), but their electron count is different from a neutral atom. This charge difference is what makes ions so reactive and important in forming compounds.

Remember: Protons never change - only electrons can be gained or lost to form ions!

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 Biology

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

b1: cell biology - paper 1

Biology

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

Forces and Motion Overview

Explore key concepts in Forces and Motion, including Hooke's Law, velocity, acceleration, and the principles of moments. This summary covers essential topics such as the relationship between force and extension, terminal velocity, and the impact of safety devices in physics. Ideal for AQA Physics Unit 5 revision.

Physics

Biology paper 1 Summary

Notes for Biology paper 1 contains the full course for AQA higher combined!

Biology

Cell Biology and Cell structure

cell structures

Biology

GCSE Biology Practicals Overview

Explore essential GCSE Biology practicals covering key concepts such as photosynthesis, enzyme activity, microbial growth, and experimental design. This comprehensive guide includes step-by-step procedures, potential errors, and calculations for each practical, ensuring a solid understanding of biological processes and laboratory techniques.

Biology

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

GCSE Physics Practical Experiments

Explore essential GCSE Physics practicals for AQA, covering key concepts such as Hooke's Law, wave properties, thermal insulation, and electrical circuits. This comprehensive guide includes step-by-step procedures, variables, and safety considerations for each experiment, ensuring a thorough understanding of practical applications in physics.

Physics

The functions of subcellular structures - B1 Biology

Flashcards on the different functions of subcellular structures: cell membrane, nucleus, mitochondria, ribosomes, cytoplasm, permant vacuole, chloroplasts and cell wall.

Biology

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

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

Combined Science

•

480

•

Updated Apr 4, 2026

•

2 pages

Understanding Atomic and Mass Numbers, Isotopes, and Ions

RiceFarmer

@ricefarmer_jhrs

Ever wondered what makes each element unique on the periodic table? It's all about the tiny particles inside atoms - protons, neutrons, and electrons - and how they can change to create different versions of the same element or give... Show more

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

Atomic and Mass Numbers

Understanding atoms is like cracking a secret code that's written right on the periodic table. Every element has two crucial numbers that tell you exactly what's happening inside its atoms.

Quick Check: Try finding the protons, neutrons, and electrons for magnesium (Mg), calcium (Ca), and potassium (K) using a periodic table!

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

Ions

Negative ions work the opposite way - they form when atoms gain extra electrons. Now there are more negatively charged electrons than positive protons, giving the ion an overall negative charge.

Remember: Protons never change - only electrons can be gained or lost to form ions!