1.1.16

Relative Atomic Mass

Test yourself on Relative Atomic Mass

Test your knowledge with free interactive questions on Seneca — used by over 10 million students.

Relative Atomic Mass (Ar)

The relative atomic mass (Ar) is the average mass of all of the isotopes of an element. It takes into account how often each isotope is found (the isotope abundance).

Calculating relative atomic masses (A<sub>r</sub>)

Calculating relative atomic masses (Ar)

  • We can calculate relative atomic masses (Ar) using the expression shown above.
Equation explained

Equation explained

  • The Σ means 'sum of'.
  • The numerator is 'the sum of the isotope abundance times the isotope mass number'.
  • The denominator is 'the sum of all the isotope abundances'.
E.g. A<sub>r</sub> of chlorine

E.g. Ar of chlorine

  • Cl may exist as 2 isotopes, 35Cl and 37Cl.
  • Isotope abundances:
    • 75% 35Cl
    • 25% 37Cl
      • Ar = [(75 x 35) + (25 x 37)] / 100 = 35.5.
Jump to other topics
1

Atomic Structure

1.1

Atoms & Elements

1.1.1Elements & Compounds1.1.2Chemical Formula1.1.3Chemical Reactions1.1.4Chemical Equations1.1.5Mixtures1.1.6Separating Mixtures1.1.7Separating Mixtures 21.1.8Model of the Atom1.1.9Sub-Atomic Particles1.1.10Atom Size1.1.11Atomic Number1.1.12Atomic Number - Calculations1.1.13Isotopes1.1.14Isotopes HyperLearning1.1.15Isotopes - Calculations1.1.16Relative Atomic Mass1.1.17Electron Structure1.1.18Periodic Table1.1.19The History of the Periodic Table1.1.20Metals & Non-Metals1.1.21Noble Gases1.1.22Displacement Reaction1.1.23Halogens1.1.24Alkali Metals1.1.25Alkali Metals - Properties1.1.26Transition Metals1.1.27Transition Metals - Special Properties1.1.28End of Topic Test - Atomic Structure1.1.29Grade 9 - Atoms & Elements1.1.30Exam-Style Questions - Atomic Structure1.1.31Application Questions - Atomic Structure1.1.32Diagnostic Misconceptions - Balancing Equations1.1.33Diagnostic Misconceptions - Isotopes
2

Chemical Bonding

2.1

Chemical Bonds

2.1.1Types of Bonds2.1.2Ions2.1.3Ionic Bonds2.1.4Ionic Compounds2.1.5Empirical Formulae2.1.6Covalent Bonds2.1.7Metallic Bonds2.1.8Covalent Bond Examples2.1.9Representing Covalent Bonds2.1.10Dots-And-Cross Diagrams2.1.11Dots-And-Cross Diagrams 22.1.12Exam-Style Questions - Chemical Bonds
2.2

States of Matter

2.2.1States of Matter2.2.2Simple Sphere2.2.3Changing State2.2.4Changing State 22.2.5Changing State HyperLearning2.2.6State Symbols2.2.7Exam-Style Questions - States of Matter2.2.8Diagnostic Misconceptions - Particles
2.3

Chemical Properties

2.3.1Ionic Compounds2.3.2Chemical Properties of Ionic Compounds2.3.3Small Molecules2.3.4Chemical Properties of Small Molecules2.3.5Molecular Forces - Polymers2.3.6Molecular Forces - Polypropene2.3.7Giant Covalent Structures2.3.8Metals2.3.9Alloys2.3.10Conductors2.3.11Carbon Structures - Diamond2.3.12Carbon Structures - Graphite2.3.13Carbon Structures - Graphene2.3.14Carbon Structures - Fullerenes2.3.15Carbon Structures - Summary2.3.16Clumps2.3.17Nanoparticles2.3.18Nanotechnology2.3.19Nanotechnology 22.3.20Surface Area to Volume Ratio2.3.21Nanotechnology Uses2.3.22End of Topic Test - Chemical Bonding2.3.23Grade 9 - Bonding & Structure2.3.24Exam-Style Questions - Allotropes of Carbon2.3.25Diagnostic Misconceptions - Conducting Electricity2.3.26Diagnostic Misconceptions - Small Molecules2.3.27Diagnostic Misconceptions - Drawing Polymers
3

Quantitative Chemistry

3.1

Chemical Measurements

3.1.1Conservation of Mass3.1.2Relative Formula Mass3.1.3Calculating Relative Formula Mass3.1.4Relative Formula Mass - Calculations3.1.5Changing Mass3.1.6Measuring Mass3.1.7Equations3.1.8Empirical Formula3.1.9Introducing Moles3.1.10Relative Formula Mass3.1.11Amounts of Substance3.1.12Moles to Balance Equations3.1.13Limiting Reactants3.1.14Concentration of Solutions3.1.15Moles - Calculations3.1.16Percentage Yield3.1.17Calculating Yield3.1.18Percentage Yield - Calculations3.1.19Moles & Yield3.1.20Moles & Yield 23.1.21Atom Economy3.1.22Reaction Pathway3.1.23Atom Economy - Calculations3.1.24Concentrations of Solute3.1.25Calculating the Amount of Solute3.1.26Amount of Substance in Relation to Volumes and Gas3.1.27Concentrations & Amounts - Calculations3.1.28Empirical Formula - Calculations3.1.29End of Topic Test - Quant Chemistry3.1.30Grade 9 - Quantitative Chemistry3.1.31Exam-Style Questions - Moles3.1.32Diagnostic Misconceptions - Calculating RFM3.1.33Diagnostic Misconceptions - Moles
4

Chemical Changes

4.1

Acids, Alkalis & Redox Reactions

4.1.1Acids & Alkalis4.1.2Redox Reactions - Oxidation4.1.3Redox Reactions - Metal Oxide
4.2

Reactivity of Metals

4.2.1Reactivity Diagram4.2.2Displacement Reactions4.2.3Displacement Reactions - Halogens4.2.4Reactions with Water4.2.5Reactions with Acid4.2.6Reactivity Tests4.2.7Reactivity Tests 24.2.8Extraction of Metals4.2.9Exam-Style Questions - Displacement Reactions
4.3

Reactions of Acids

4.3.1Reactions of Metals with Acids4.3.2Redox Reactions4.3.3Neutralisation of Acids4.3.4Soluble Salts4.3.5Required Practical: Separating Mixtures4.3.6The pH Scale4.3.7Numerical pH Scale4.3.8Measuring pH4.3.9Neutralisation & Titrations4.3.10Neutralisation & Titrations 24.3.11Neutralisation & Titrations 34.3.12Neutralisation & Titrations 44.3.13Strong and Weak Acids4.3.14Required Practical: Titration
4.4

Electrolysis

4.4.1Electrolysis Process4.4.2Molten Ionic Compound4.4.3Metal Extraction4.4.4Electrolysis of Aqueous Solutions4.4.5Required Practical: Electrolysis4.4.6Half Equations4.4.7End of Topic Test - Chemical Changes4.4.8Grade 9 - Chemical Changes4.4.9Exam-Style Questions - Electrolysis
5

Energy Changes

5.1

Exothermic & Endothermic Reactions

5.1.1Energy Conservation5.1.2Exothermic Reactions5.1.3Endothermic Reactions5.1.4Required Practical: Temperature Changes5.1.5Reaction Profiles Requirements5.1.6Reaction Profiles5.1.7Reaction Profiles - Catalysed vs Uncatalysed5.1.8Reaction Profiles - Chemical Bonds5.1.9Diagnostic Misconceptions - Source of Energy
5.2

Chemical Cells & Fuel Cells

5.2.1Chemical Cells5.2.2Changing Voltage Output5.2.3Batteries5.2.4Charging of Cells5.2.5Fuel Cells5.2.6Hydrogen Fuel Cell5.2.7Hydrogen as an Alternative5.2.8End of Topic Test - Energy Changes5.2.9Grade 9 - Energy Changes5.2.10Exam-Style Questions - Fuel Cells
6

The Rate & Extent of Chemical Change

6.1

Rate of Reaction

6.1.1Chemical Reactions6.1.2Plotting Reaction Rates6.1.3Required Practical: Effect of Concentration6.1.4Collision Theory6.1.5Key Factors of Rate of Reaction6.1.6Catalysts6.1.7Catalysts in Industry
6.2

Reversible Reactions

6.2.1Reversible Reactions6.2.2Dynamic Equilibrium6.2.3Conditions and Equilibrium6.2.4Equilibrium Position - Temperature6.2.5Equilibrium Position - Pressure6.2.6Equilibrium Position - Concentration6.2.7End of Topic Test - Rates of Reaction6.2.8Grade 9 - Rate & Extent of Chemical Change6.2.9Exam-Style Questions - Reversible Reactions6.2.10Diagnostic Misconceptions - Temperature6.2.11Diagnostic Misconceptions - Pressure6.2.12Diagnostic Misconceptions - Concentration6.2.13Diagnostic Misconceptions - Catalysts
7

Organic Chemistry

7.1

Carbon Compounds

7.1.1Crude Oil7.1.2Properties of Hydrocarbons7.1.3Alkanes7.1.4Smallest Alkanes7.1.5Fractional Distillation7.1.6Process of Fractional Distillation7.1.7Homologous Series7.1.8Burning Hydrocarbons7.1.9Heavy Fractions of Crude Oil7.1.10Cracking7.1.11Uses of Alkenes7.1.12Exam-Style Questions - Organic Compounds
7.2

Alkenes & Alcohols

7.2.1Structure of Alkenes7.2.2The Shortest Alkenes7.2.3Reactions of Alkenes7.2.4Types of Alkene Reactions7.2.5Alcohols7.2.6The Smallest Alcohols7.2.7Reactions of Alcohols7.2.8Fermentation7.2.9Carboxylic Acids7.2.10The Smallest Carboxylic Acids7.2.11Reactions of Carboxylic Acids7.2.12Addition Polymers7.2.13Addition Polymers Examples7.2.14Condensation Polymers7.2.15Amino Acids7.2.16Naturally Occurring Polymers - Protein (Formation)7.2.17Naturally Occurring Polymers - Protein (Roles)7.2.18Naturally Occurring Polymers - DNA7.2.19Naturally Occurring Polymers - Others7.2.20End of Topic Test - Alkanes & Alkenes7.2.21End of Topic Test - Alcohols, Acids & Polymers7.2.22Grade 9 - Organic Chemistry7.2.23Exam-Style Questions - Alcohols
8

Chemical Analysis

8.1

Purity, Formulations & Chromatography

8.1.1Purity8.1.2Formulations8.1.3Chromatography8.1.4Paper Chromatography 18.1.5Paper Chromatography 28.1.6Required Practical - Paper Chromatography8.1.7Diagnostic Misconceptions - Purity
8.2

Identification of Common Gases

8.2.1Identification of Hydrogen8.2.2Identification of Oxygen8.2.3Identification of Carbon Dioxide8.2.4Identification of Chlorine
8.3

Identifying Ions

8.3.1Flame Tests8.3.2Required Practical: Flame Tests8.3.3Metal Hydroxides8.3.4Metal Hydroxides 28.3.5Carbonates8.3.6Halides8.3.7Sulfates8.3.8Methodology for Chemical Analysis8.3.9Methodology for Chemical Analysis 28.3.10Flame Emission Spectroscopy8.3.11Flame Emission Spectroscopy Analysis8.3.12End of Topic Test - Chemical Analysis8.3.13Grade 9 - Chemical Analysis8.3.14Exam-Style Questions - Identification of ions
9

Chemistry of the Atmosphere

9.1

The Earth's Atmosphere

9.1.1Proportions of Gases in the Atmosphere9.1.2The Earth's Early Atmosphere9.1.3Oxygen in the Atmosphere9.1.4Carbon Dioxide in the Atmosphere9.1.5Greenhouse Gases9.1.6Greenhouse Gases & Human Activities9.1.7Greenhouse Gases & Climate9.1.8Climate Change9.1.9Carbon Footprints9.1.10Carbon Footprints Barriers9.1.11Common Atmospheric Pollutants9.1.12Properties of Atmospheric Pollutants9.1.13End of Topic Test - The Earth9.1.14Grade 9 - Chemistry of the Atmosphere9.1.15Exam-Style Questions - Earth's Atmosphere9.1.16Diagnostic Misconceptions - Greenhouse Effect
10

Using Resources

10.1

Using the Earth's Resources

10.1.1Potable Water10.1.2Potable Water Sources10.1.3Potable Water in the UK10.1.4Potable Water in Saudi Arabia10.1.5Required Practical: Analysing and Purifying Water10.1.6Natural Resources10.1.7Uses of Natural Resources10.1.8Waste Water10.1.9Sewage Treatment10.1.10Metal Ore Extraction10.1.11Properties of Copper10.1.12Overexploitation of Extraction Methods10.1.13Alternative Extraction Methods
10.2

Life Cycle Assessments & Recycling

10.2.1Life Cycle Assessments10.2.2Comparative Life Cycle Assessments10.2.3Difficulties with LCA10.2.4Reducing Resource Usage10.2.5Reducing Use of Glass10.2.6Reducing Use of Metal10.2.7Exam-Style Questions - Life Cycle Assessments
10.3

Using Materials

10.3.1Corrosion10.3.2Preventing Corrosion10.3.3Alloys10.3.4Ceramics10.3.5Polymers10.3.6Composites
10.4

The Haber Process & NPK Fertilisers

10.4.1Plants and Nitrogen10.4.2The Haber Process10.4.3The Haber Process - Equation10.4.4The Haber Process - Trade-Offs10.4.5Importance of Fertilisers10.4.6Formulated vs Manure Fertilisers10.4.7NPK Fertilisers - N-containing Compound10.4.8NPK Fertilisers - P-containing Compound10.4.9NPK Fertilisers - K-containing Compound10.4.10Nitrogen, Phosphorus and Potassium10.4.11End of Topic Test - Resources10.4.12Grade 9 - Using Resources10.4.13Exam-Style Questions - The Haber Process

Practice questions on Relative Atomic Mass

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    75% of Cl atoms have a mass number of 35, whilst the remaining 25% have a mass number of 37. What is the relative atomic mass of chlorine?Multiple choice
  2. 2
    What is the symbol for relative atomic mass?Multiple choice
Answer all questions on Relative Atomic Mass

Unlock your full potential with Seneca Premium

  • Unlimited access to 10,000+ open-ended exam questions

  • Mini-mock exams based on your study history

  • Unlock 800+ premium courses & e-books

Get started with Seneca Premium

Isotopes - Calculations

Electron Structure