Atomic masses of elements can be found by simply looking at the periodic table. So let's start off by looking at the symbol of H, which represents hydrogen. And if you take a look at hydrogen as well as the other elements on the periodic table, you'll see these whole numbers. These whole numbers represent our atomic number. They are the number of protons. When we say atomic mass though, the atomic mass is the number that is seldom a whole number. This is our atomic mass. So you can find the atomic mass of any element on the periodic table just by simply looking it up. Now we're going to say the atomic mass itself is an average of all its isotopes that use the units of grams per mole, AMU, or Daltons, and we're going to say remember that 1 AMU equals 1.66 × 10 - 27 kilograms. So just remember, these atomic masses that you see on the periodic table, they are usually not whole numbers. You'd have to get way down below here to these heavy elements down here till you see whole numbers for atomic masses. And remember, they are the average of all the isotopes for that given element.
- 1. Matter and Measurements4h 29m
- What is Chemistry?5m
- The Scientific Method9m
- Classification of Matter16m
- States of Matter8m
- Physical & Chemical Changes19m
- Chemical Properties8m
- Physical Properties5m
- Intensive vs. Extensive Properties13m
- Temperature (Simplified)9m
- Scientific Notation13m
- SI Units (Simplified)5m
- Metric Prefixes24m
- Significant Figures (Simplified)11m
- Significant Figures: Precision in Measurements7m
- Significant Figures: In Calculations19m
- Conversion Factors (Simplified)15m
- Dimensional Analysis22m
- Density12m
- Specific Gravity9m
- Density of Geometric Objects19m
- Density of Non-Geometric Objects9m
- 2. Atoms and the Periodic Table5h 23m
- The Atom (Simplified)9m
- Subatomic Particles (Simplified)12m
- Isotopes17m
- Ions (Simplified)22m
- Atomic Mass (Simplified)17m
- Atomic Mass (Conceptual)12m
- Periodic Table: Element Symbols6m
- Periodic Table: Classifications11m
- Periodic Table: Group Names8m
- Periodic Table: Representative Elements & Transition Metals7m
- Periodic Table: Elemental Forms (Simplified)6m
- Periodic Table: Phases (Simplified)8m
- Law of Definite Proportions9m
- Atomic Theory9m
- Rutherford Gold Foil Experiment9m
- Wavelength and Frequency (Simplified)5m
- Electromagnetic Spectrum (Simplified)11m
- Bohr Model (Simplified)9m
- Emission Spectrum (Simplified)3m
- Electronic Structure4m
- Electronic Structure: Shells5m
- Electronic Structure: Subshells4m
- Electronic Structure: Orbitals11m
- Electronic Structure: Electron Spin3m
- Electronic Structure: Number of Electrons4m
- The Electron Configuration (Simplified)22m
- Electron Arrangements5m
- The Electron Configuration: Condensed4m
- The Electron Configuration: Exceptions (Simplified)12m
- Ions and the Octet Rule9m
- Ions and the Octet Rule (Simplified)8m
- Valence Electrons of Elements (Simplified)5m
- Lewis Dot Symbols (Simplified)7m
- Periodic Trend: Metallic Character4m
- Periodic Trend: Atomic Radius (Simplified)7m
- 3. Ionic Compounds2h 18m
- Periodic Table: Main Group Element Charges12m
- Periodic Table: Transition Metal Charges6m
- Periodic Trend: Ionic Radius (Simplified)5m
- Periodic Trend: Ranking Ionic Radii8m
- Periodic Trend: Ionization Energy (Simplified)9m
- Periodic Trend: Electron Affinity (Simplified)8m
- Ionic Bonding6m
- Naming Monoatomic Cations6m
- Naming Monoatomic Anions5m
- Polyatomic Ions25m
- Naming Ionic Compounds11m
- Writing Formula Units of Ionic Compounds7m
- Naming Ionic Hydrates6m
- Naming Acids18m
- 4. Molecular Compounds2h 18m
- Covalent Bonds6m
- Naming Binary Molecular Compounds6m
- Molecular Models4m
- Bonding Preferences6m
- Lewis Dot Structures: Neutral Compounds (Simplified)8m
- Multiple Bonds4m
- Multiple Bonds (Simplified)6m
- Lewis Dot Structures: Multiple Bonds10m
- Lewis Dot Structures: Ions (Simplified)8m
- Lewis Dot Structures: Exceptions (Simplified)12m
- Resonance Structures (Simplified)5m
- Valence Shell Electron Pair Repulsion Theory (Simplified)4m
- Electron Geometry (Simplified)8m
- Molecular Geometry (Simplified)11m
- Bond Angles (Simplified)11m
- Dipole Moment (Simplified)15m
- Molecular Polarity (Simplified)7m
- 5. Classification & Balancing of Chemical Reactions3h 17m
- Chemical Reaction: Chemical Change5m
- Law of Conservation of Mass5m
- Balancing Chemical Equations (Simplified)13m
- Solubility Rules16m
- Molecular Equations18m
- Types of Chemical Reactions12m
- Complete Ionic Equations18m
- Calculate Oxidation Numbers15m
- Redox Reactions17m
- Spontaneous Redox Reactions8m
- Balancing Redox Reactions: Acidic Solutions17m
- Balancing Redox Reactions: Basic Solutions17m
- Balancing Redox Reactions (Simplified)13m
- Galvanic Cell (Simplified)16m
- 6. Chemical Reactions & Quantities2h 35m
- 7. Energy, Rate and Equilibrium3h 46m
- Nature of Energy6m
- First Law of Thermodynamics7m
- Endothermic & Exothermic Reactions7m
- Bond Energy14m
- Thermochemical Equations12m
- Heat Capacity19m
- Thermal Equilibrium (Simplified)8m
- Hess's Law23m
- Rate of Reaction11m
- Energy Diagrams12m
- Chemical Equilibrium7m
- The Equilibrium Constant14m
- Le Chatelier's Principle23m
- Solubility Product Constant (Ksp)17m
- Spontaneous Reaction10m
- Entropy (Simplified)9m
- Gibbs Free Energy (Simplified)18m
- 8. Gases, Liquids and Solids3h 25m
- Pressure Units6m
- Kinetic Molecular Theory14m
- The Ideal Gas Law18m
- The Ideal Gas Law Derivations13m
- The Ideal Gas Law Applications6m
- Chemistry Gas Laws16m
- Chemistry Gas Laws: Combined Gas Law12m
- Standard Temperature and Pressure14m
- Dalton's Law: Partial Pressure (Simplified)13m
- Gas Stoichiometry18m
- Intermolecular Forces (Simplified)19m
- Intermolecular Forces and Physical Properties11m
- Atomic, Ionic and Molecular Solids10m
- Heating and Cooling Curves30m
- 9. Solutions4h 10m
- Solutions6m
- Solubility and Intermolecular Forces18m
- Solutions: Mass Percent6m
- Percent Concentrations10m
- Molarity18m
- Osmolarity15m
- Parts per Million (ppm)13m
- Solubility: Temperature Effect8m
- Intro to Henry's Law4m
- Henry's Law Calculations12m
- Dilutions12m
- Solution Stoichiometry14m
- Electrolytes (Simplified)13m
- Equivalents11m
- Molality15m
- The Colligative Properties15m
- Boiling Point Elevation16m
- Freezing Point Depression9m
- Osmosis16m
- Osmotic Pressure9m
- 10. Acids and Bases3h 29m
- Acid-Base Introduction11m
- Arrhenius Acid and Base6m
- Bronsted Lowry Acid and Base18m
- Acid and Base Strength17m
- Ka and Kb12m
- The pH Scale19m
- Auto-Ionization9m
- pH of Strong Acids and Bases9m
- Acid-Base Equivalents14m
- Acid-Base Reactions7m
- Gas Evolution Equations (Simplified)6m
- Ionic Salts (Simplified)23m
- Buffers25m
- Henderson-Hasselbalch Equation16m
- Strong Acid Strong Base Titrations (Simplified)10m
- 11. Nuclear Chemistry56m
- BONUS: Lab Techniques and Procedures1h 38m
- BONUS: Mathematical Operations and Functions47m
- 12. Introduction to Organic Chemistry1h 34m
- 13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
- 14. Compounds with Oxygen or Sulfur1h 6m
- 15. Aldehydes and Ketones1h 1m
- 16. Carboxylic Acids and Their Derivatives1h 11m
- 17. Amines38m
- 18. Amino Acids and Proteins1h 51m
- 19. Enzymes1h 37m
- 20. Carbohydrates1h 46m
- Intro to Carbohydrates4m
- Classification of Carbohydrates4m
- Fischer Projections4m
- Enantiomers vs Diastereomers8m
- D vs L Enantiomers8m
- Cyclic Hemiacetals8m
- Intro to Haworth Projections4m
- Cyclic Structures of Monosaccharides11m
- Mutarotation4m
- Reduction of Monosaccharides10m
- Oxidation of Monosaccharides7m
- Glycosidic Linkage14m
- Disaccharides7m
- Polysaccharides7m
- 21. The Generation of Biochemical Energy2h 8m
- 22. Carbohydrate Metabolism2h 22m
- 23. Lipids2h 26m
- Intro to Lipids6m
- Fatty Acids25m
- Physical Properties of Fatty Acids6m
- Waxes4m
- Triacylglycerols12m
- Triacylglycerol Reactions: Hydrogenation8m
- Triacylglycerol Reactions: Hydrolysis13m
- Triacylglycerol Reactions: Oxidation7m
- Glycerophospholipids15m
- Sphingomyelins13m
- Steroids15m
- Cell Membranes7m
- Membrane Transport10m
- 24. Lipid Metabolism1h 45m
- 25. Protein and Amino Acid Metabolism1h 37m
- 26. Nucleic Acids and Protein Synthesis2h 54m
- Intro to Nucleic Acids4m
- Nitrogenous Bases16m
- Nucleoside and Nucleotide Formation9m
- Naming Nucleosides and Nucleotides13m
- Phosphodiester Bond Formation7m
- Primary Structure of Nucleic Acids11m
- Base Pairing10m
- DNA Double Helix6m
- Intro to DNA Replication20m
- Steps of DNA Replication11m
- Types of RNA10m
- Overview of Protein Synthesis4m
- Transcription: mRNA Synthesis9m
- Processing of pre-mRNA5m
- The Genetic Code6m
- Introduction to Translation7m
- Translation: Protein Synthesis18m
Atomic Mass (Conceptual) - Online Tutor, Practice Problems & Exam Prep
Atomic masses of elements, found on the periodic table, represent averages of all isotopes and are typically not whole numbers. The most abundant isotope is the one with a mass number closest to the atomic mass. For example, hydrogen's atomic mass is 1.008 amu, with hydrogen-1 being the most abundant. Similarly, boron has an atomic mass of 10.81 amu, making boron-11 the most abundant isotope. Understanding isotopes and atomic mass is crucial for grasping concepts in chemistry, including reactions and molecular behavior.
The atomic mass of an element can be found on the Periodic Table.
Determining Atomic Mass
Atomic Mass (Conceptual) Concept 1
Video transcript
Atomic Mass (Conceptual) Example 1
Video transcript
So here for this example question, it says, which of the following represents an element from the first column with the greatest atomic mass? Alright. So our first column, if we look at this periodic table, includes all of these different elements. And remember, the number in red, which is not a whole number normally, that represents the atomic mass of any of these given elements. Now here, if we take a look, we have barium, Ba. Again, later we'll learn about how the names are attached to the element symbol. Ba is not in the 1st column; here it's in the 2nd column. So this cannot be a choice. Then we're going to say next that we have Al. Al stands for aluminum. Aluminum is over here in the 3rd column, well, all the way over here in this 13th column, actually. So, this is out. Next, we have Cs, which is cesium. Here it is right here. It's in the first column. It's pretty low down there. It's 132.91 for its atomic mass. Remember, that could be in grams per mole, atomic mass units, or Daltons. So far, it looks like it's the highest one. The only one higher than that would be Fr. Notice that in the bottom rows here, most of them are whole numbers. These are super large mass elements that are pretty unstable. They typically don't have numerous isotopes. As a result, they have no decimal places. So, so far C looks like it's our best choice. If we look at D, we have Li, which is up here, not higher in mass, not greater in atomic mass. And then we have Na, which is right here. So it looks like C is our best choice. It has the greatest mass, atomic mass, from column 1 from the choices provided. So just remember we have our element symbols, we have our atomic masses, which normally are not whole numbers, and then we actually have whole numbers. Those represent our atomic numbers.
On the Periodic Table, the atomic mass is represented by the number with decimal places.
Which of the following choices has the greatest atomic mass?
Atomic Mass (Conceptual) Concept 2
Video transcript
When dealing with isotopes, we can talk about the most abundant isotope. Recall, the atomic mass of an element is an average mass of all its isotopes, and we're going to say that the most abundant isotope for an element is the one with a mass number closest to the atomic mass of the element. Remember, your mass number gives you the number of protons and neutrons together for a given isotope. So if we take a look here, we have our element, their atomic mass, the isotope symbols, and then we talk about their most abundant isotope. So for hydrogen, its atomic mass, according to the periodic table, is 1.008 amu and its isotope symbols are hydrogen. When it has a mass number of 2 it's called deuterium, and when it has a mass number of 3, it's called tritium. Alright. Now, remember, we said that the most abundant isotope is the one that has a mass number closest to the atomic mass. The atomic mass is 1. Here are our mass numbers, 1, 2, and 3. The one closest to the atomic mass is hydrogen-1. Its atomic mass number is 1 and it's closest to the atomic mass of 1.008.
Let's go to the next one, boron. Boron has two forms, boron-10 and boron-11. The atomic mass of boron is 10.81 amu. Looking at boron-10 and boron-11, which one has a mass number closest to this atomic mass? The answer would be boron-11 because 11 is closer to 10.81 than 10 is.
Then finally, we have sulfur. Sulfur has an atomic mass of 32.06 amu when you look on the periodic table. Alright? Now, some versions might show 32.07, but then remember, it's okay. It can either be 32.06 or 32.07, depending on which periodic table you are looking at. But that doesn't matter. Here is my atomic mass. Which mass number is closest to that 32.06? And we see that the answer is sulfur-32. 32 is closer to 32.06 than either 33, 34, or 36. Alright. So just remember, the most abundant isotope, to figure it out, look at what the atomic mass of the element is on the periodic table, look at the different mass numbers for all the isotopes, the one that has a mass number closest to that atomic mass is the most abundant isotope.
Atomic Mass (Conceptual) Example 2
Video transcript
Oxygen consists of 3 isotopes, oxygen-16, oxygen-17, and oxygen-18. If the atomic mass for oxygen on the periodic table is 15.999 AMU, which isotope is the most abundant? So remember, we look at the atomic mass, which you can find on the periodic table for the element, and then you look to see which mass number is closest to it. The one closest to it represents the most abundant isotope. Oxygen-16 would have to be the answer because its number of 16 is closest to the atomic mass of 15.999 AMU.
Vanadium consists of two isotopes, 5023V and 5123V. If the atomic mass for copper on the periodic table is 50.942 amu, are there more atoms of 5023V and 5123V in a sample of vanadium?
Potassium consists of three isotopes, 3919K, 4019K, and 4119K. Based on its atomic mass, which isotope of potassium is the most abundant?
Do you want more practice?
Here’s what students ask on this topic:
What is the atomic mass of an element and how is it determined?
The atomic mass of an element is the weighted average mass of all its isotopes, measured in atomic mass units (amu). It is determined by taking into account the mass and relative abundance of each isotope of the element. The atomic mass is typically not a whole number because it reflects the average of the different isotopic masses. For example, the atomic mass of hydrogen is 1.008 amu, which is an average of its isotopes hydrogen-1, deuterium (hydrogen-2), and tritium (hydrogen-3).
Why are atomic masses on the periodic table usually not whole numbers?
Atomic masses on the periodic table are usually not whole numbers because they represent the weighted average of all the isotopes of an element, taking into account their relative abundances. Each isotope has a different mass number, and the atomic mass is calculated by averaging these masses based on how common each isotope is. For instance, chlorine has isotopes with mass numbers 35 and 37, and its atomic mass is approximately 35.45 amu, reflecting the average of these isotopes.
How do you determine the most abundant isotope of an element?
To determine the most abundant isotope of an element, look at the atomic mass of the element on the periodic table and compare it to the mass numbers of its isotopes. The isotope with the mass number closest to the atomic mass is the most abundant. For example, hydrogen has an atomic mass of 1.008 amu, and its isotopes are hydrogen-1, deuterium (hydrogen-2), and tritium (hydrogen-3). Since hydrogen-1 has a mass number of 1, which is closest to 1.008, it is the most abundant isotope.
What is the relationship between atomic mass and isotopes?
The atomic mass of an element is directly related to its isotopes. It is the weighted average of the masses of all the isotopes of that element, considering their relative abundances. Each isotope has a different number of neutrons, resulting in different mass numbers. The atomic mass reflects the average mass of these isotopes, which is why it is usually not a whole number. For example, carbon has isotopes carbon-12 and carbon-13, and its atomic mass is approximately 12.01 amu, reflecting the average mass of these isotopes.
How is the atomic mass unit (amu) defined and what is its significance?
The atomic mass unit (amu) is defined as one-twelfth the mass of a carbon-12 atom, which is approximately 1.66 × 10-27 kilograms. It is a standard unit of mass used to express atomic and molecular weights. The significance of the amu lies in its ability to provide a convenient scale for comparing the masses of different atoms and molecules. For example, the atomic mass of hydrogen is 1.008 amu, meaning it is slightly heavier than one amu, while oxygen has an atomic mass of 16.00 amu, indicating it is 16 times heavier than one amu.