Learn Relative Atomic Mass, First Ionisation Energy, and Formula Differences

A* on the way

11/10/2025

Chemistry

A level chemistry definitions

Subjects

Chemistry

Physical chemistry

Amount of substance

1,025

•

11 Oct 2025

•

7 pages

Learn Relative Atomic Mass, First Ionisation Energy, and Formula Differences

Name: Knowunity
Brand: Knowunity

A* on the way

@x30sciencea

The relative atomic mass in chemistry is a fundamental concept... Show more

1 / 7

AQA A LEVEL CHEMISTRY - DEFINITION LIST
Atomic structure
Isotope:
An atom of the same element that has the same number of protons and electr

Bonding and Molecular Concepts

This section explores various types of chemical bonding and molecular structure concepts. It covers metallic, covalent, and ionic bonding, along with important molecular calculations.

Definition: Atom economy measures reaction efficiency by comparing desired product mass to total product masses.

Vocabulary: Electronegativity refers to an atom's ability to attract bonding electrons in a covalent bond.

Example: A dative covalent bond forms when one atom provides both electrons in the shared pair.

Highlight: Understanding different bonding types is essential for predicting molecular properties and chemical behavior.

Energetics and Reaction Processes

This section details energy changes in chemical reactions, including enthalpy changes and bond energies.

Definition: Enthalpy change represents heat energy changes measured at constant pressure.

Vocabulary: Activation energy is the minimum energy required to initiate a reaction through bond breaking.

Example: Exothermic reactions release heat energy (negative values), while endothermic reactions absorb heat energy (positive values).

Highlight: Bond enthalpy calculations are crucial for predicting overall reaction energetics.

Kinetics and Equilibria

This section covers reaction rates and equilibrium concepts, including Le Chatelier's Principle.

Definition: Reaction rate measures the change in concentration of reactants or products over time.

Quote: "Le Chatelier's Principle states that when a reaction at equilibrium is subjected to change, the position of equilibrium moves to counteract that change."

Highlight: Understanding kinetics and equilibria is essential for controlling industrial chemical processes.

Organic Chemistry Fundamentals

This section introduces basic organic chemistry concepts, including hydrocarbon classification and molecular representations.

Definition: A hydrocarbon is a compound containing only hydrogen and carbon atoms.

Vocabulary: Saturated compounds contain only single carbon-carbon bonds, while unsaturated compounds have at least one double bond.

Example: Different formula representations include displayed, structural, and skeletal formulas.

Molecular Representations

This section focuses on various ways to represent molecular structures in organic chemistry.

Definition: The molecular formula shows the actual number of atoms of each element in a compound.

Example: CH3CH2OH can be represented in multiple ways: displayed, structural, or skeletal formula.

Highlight: Understanding different molecular representations is crucial for organic chemistry comprehension.

Organic Chemistry Classifications

This section covers the classification of organic compounds and their functional groups.

Definition: A homologous series is a family of compounds with the same functional group and general formula, differing by CH2 units.

Vocabulary: Functional groups are specific atoms or groups that determine compound properties.

Highlight: Recognition of functional groups is essential for predicting chemical behavior and reactions.

Atomic Structure and Basic Definitions

This section introduces fundamental atomic concepts and definitions essential for understanding chemistry at an advanced level. The content focuses on isotopes, relative atomic mass, and ionization energy.

Definition: Relative atomic mass is defined as the weighted mean mass of an atom compared with 1/12th of the mass of carbon-12.

Vocabulary: Isotopes are atoms of the same element with identical proton and electron numbers but different neutron counts.

Example: The first ionisation energy process can be represented as X $g$ → X $g$ + + e-, where energy is required to remove one electron from a gaseous atom.

Highlight: Understanding relative atomic mass calculations is crucial for determining molecular masses and stoichiometry in chemical reactions.

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.

Students love us — and so will you.

4.9/5

App Store

4.8/5

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 THE SCHOOLGPT. 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

Subjects

Chemistry

Physical chemistry

Amount of substance

Chemistry

11 Oct 2025

1,025

7 pages

Learn Relative Atomic Mass, First Ionisation Energy, and Formula Differences

A* on the way @x30sciencea

The relative atomic mass in chemistry is a fundamental concept that helps understand atomic structure and chemical calculations. This comprehensive guide covers key definitions in atomic structure, amount of substance,... Show more

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Bonding and Molecular Concepts

This section explores various types of chemical bonding and molecular structure concepts. It covers metallic, covalent, and ionic bonding, along with important molecular calculations.

Definition Atom economy measures reaction efficiency by comparing desired product mass to total product masses.

Vocabulary Electronegativity refers to an atom's ability to attract bonding electrons in a covalent bond.

Example A dative covalent bond forms when one atom provides both electrons in the shared pair.

Highlight Understanding different bonding types is essential for predicting molecular properties and chemical behavior.

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Energetics and Reaction Processes

This section details energy changes in chemical reactions, including enthalpy changes and bond energies.

Definition Enthalpy change represents heat energy changes measured at constant pressure.

Vocabulary Activation energy is the minimum energy required to initiate a reaction through bond breaking.

Example Exothermic reactions release heat energy (negative values), while endothermic reactions absorb heat energy (positive values).

Highlight Bond enthalpy calculations are crucial for predicting overall reaction energetics.

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Kinetics and Equilibria

This section covers reaction rates and equilibrium concepts, including Le Chatelier's Principle.

Definition Reaction rate measures the change in concentration of reactants or products over time.

Quote "Le Chatelier's Principle states that when a reaction at equilibrium is subjected to change, the position of equilibrium moves to counteract that change."

Highlight Understanding kinetics and equilibria is essential for controlling industrial chemical processes.

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Organic Chemistry Fundamentals

This section introduces basic organic chemistry concepts, including hydrocarbon classification and molecular representations.

Definition A hydrocarbon is a compound containing only hydrogen and carbon atoms.

Vocabulary Saturated compounds contain only single carbon-carbon bonds, while unsaturated compounds have at least one double bond.

Example Different formula representations include displayed, structural, and skeletal formulas.

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Molecular Representations

This section focuses on various ways to represent molecular structures in organic chemistry.

Definition The molecular formula shows the actual number of atoms of each element in a compound.

Example CH3CH2OH can be represented in multiple ways displayed, structural, or skeletal formula.

Highlight Understanding different molecular representations is crucial for organic chemistry comprehension.

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Organic Chemistry Classifications

This section covers the classification of organic compounds and their functional groups.

Definition A homologous series is a family of compounds with the same functional group and general formula, differing by CH2 units.

Vocabulary Functional groups are specific atoms or groups that determine compound properties.

Highlight Recognition of functional groups is essential for predicting chemical behavior and reactions.

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Atomic Structure and Basic Definitions

Definition Relative atomic mass is defined as the weighted mean mass of an atom compared with 1/12th of the mass of carbon-12.

Vocabulary Isotopes are atoms of the same element with identical proton and electron numbers but different neutron counts.

Example The first ionisation energy process can be represented as X $g$ → X $g$ + + e-, where energy is required to remove one electron from a gaseous atom.

Highlight Understanding relative atomic mass calculations is crucial for determining molecular masses and stoichiometry in chemical reactions.