Back To Course

High School Physical Science: Homework Help Resource32 chapters | 343 lessons

Are you a student or a teacher?

Try Study.com, risk-free

As a member, you'll also get unlimited access to over 75,000 lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed.

Try it risk-freeWhat teachers are saying about Study.com

Already registered? Login here for access

Your next lesson will play in
10 seconds

Lesson Transcript

Instructor:
*Felicia Fullilove*

We know all matter is made of atoms, but how is the mass of an atom expressed? Explore this lesson to learn more about atomic mass units (amus), carbon-12, and amu to kilogram conversion!

How much do you weigh? No need to answer out loud, but whatever the answer, I am sure the amount was expressed in pounds or kilograms. What are you made of? You may answer organs, blood, or bones. The simplest answer, however, is atoms and molecules. An **atom** is the smallest constituent of a chemical element that has all the properties of an element. Atoms comprise every single piece of matter. From your sofa to the sandwich you ate yesterday, atoms in multiple combinations, or molecules, are all around us. But how is the mass of an atom expressed? In this lesson, we will learn more about atomic mass units.

The periodic table of elements contains every atom known to mankind. Each unique atom has a unique atomic number and atomic mass. The **atomic number** is the number of protons in the atom's nucleus, while the **atomic mass** is the mass of the atom, which is the sum of the number of protons and neutrons. The atomic mass of an element is expressed in atomic mass units. **Atomic mass units** are described as a unit of measurement for atoms and molecules, just like the mass of a person may be expressed in pounds or kilograms. Hydrogen, for example, is the first element on the periodic table and has an atomic number of 1 and an atomic mass of 1.00794 amu, or atomic mass units.

According to the International Union of Pure and Applied Chemistry (IUPAC), **1 atomic mass unit** is defined as 1/12 the mass of carbon-12. Therefore, carbon-12 has a mass of 12 amu. Carbon-12 is the most abundant isotope of carbon. An **isotope** is two or more elements with the same number of protons (atomic number) but different number of neutrons. For example, carbon-12 has 6 protons, 6 electrons, and 6 neutrons and encompasses over 98% of carbon found in nature. On the other hand, carbon-13 has 6 protons, 6 electrons, and 7 neutrons; and carbon-14 has 6 protons, 6 electrons, and 8 neutrons.

Why is carbon the standard? Good question! Carbon is commonly combined with other elements; additionally, the carbon-12 isotope is highly abundant in nature. After many years of arguing, chemists and physicists agreed that carbon-12 would be the best unit of measurement for atomic masses. Previous standards included hydrogen and oxygen; however, scientists had difficulty using these elements as standards due to the distribution of their isotopes.

If atoms are weighed in atomic mass units, how do we get from atomic mass units to a more common measurement like kilograms? Conversion! According to the Royal Society of Chemistry, one atomic mass unit is equal to 1.66 x 10^-27 kg. Where did this number come from? While the history of atomic masses is quite complicated, the conversion factor from atomic mass units to kilograms is related to the mole and Avogadro's constant.

The mole is a base unit that describes the amount of a substance. You can have a mole of anything: atoms, baseballs, and even carrots. According to the National Institute of Standards and Technology (NIST), the **mole** is 'the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilograms of carbon-12.' The number of atoms or molecules in one mole of substance is known as **Avogadro's constant (Na or L)**. Avogadro's constant, Na, is an experimentally defined number of 6.022 * 10 ^23 entities per mole (remember entities can be atoms, baseballs, or carrots).

Believe it or not, mathematically, moles and Avogadro's constant bring us back to atomic mass units.

An atomic mass unit is 1/12th the mass of carbon-12, therefore, the mass of carbon-12 is 12 amu. Consequently, one mole of carbon-12 has Avogadro's constant (Na) amount of atoms in 0.012 kg of carbon-12. Mathematically, this is expressed by:

(6.022 * 10^23/ mol) * 12 amu = 0.012 (kg/mol)

Dividing both sides of the equation by 12 we are left with:

(6.022 * 10^23/mol)(1 amu) = 0.001 kg/mol

Dividing both sides by Avogadro's constant, we find that 1 amu is equal to 1.66 * 10^-27 kg.

This means that atomic mass units can be easily converted to kilograms or grams. For example, carbon-12 has a mass of 12 amu. By multiplying 12 amu by 1.66 x 10^-27 kg/amu we find the mass of carbon-12 in kilograms is 1.99 * 10^-26 kg. This conversion can be used to convert atoms and molecules from atomic mass units to grams and kilograms.

In this lesson, we have learned that the mass of atoms and molecules are expressed in atomic mass units. **Atomic mass units (amus)**, are described as 1/12 the mass of carbon-12. Therefore, carbon-12 is identified as the standard for atomic mass. Finally, the mass of atoms and molecules can be converted from atomic mass units to kilograms by the unit conversion which states:

1 amu = 1.66 * 10^-27 kg

To unlock this lesson you must be a Study.com Member.

Create your account

Are you a student or a teacher?

Already a member? Log In

BackWhat teachers are saying about Study.com

Already registered? Login here for access

Did you know… We have over 160 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

You are viewing lesson
Lesson
15 in chapter 9 of the course:

Back To Course

High School Physical Science: Homework Help Resource32 chapters | 343 lessons

- The Photoelectric Effect: Definition, History, Application & Equation 4:30
- Energy & Momentum of a Photon: Equation & Calculations 5:07
- Planck's Constant: Formula & Application 4:31
- The Bohr Model and Atomic Spectra 8:41
- Heisenberg Uncertainty Principle: Definition & Equation 6:50
- Electron Cloud: Definition, Model & Theory 4:13
- Nuclear Physics: Nuclear Force & Building Energy 4:40
- Nuclear Reaction: Definition & Examples 5:30
- Types of Radioactive Decay and Their Effect on the Nucleus 8:26
- Balancing Nuclear Equations & Predicting the Product of a Nuclear Reaction 7:37
- Half-life: Calculating Radioactive Decay and Interpreting Decay Graphs 6:33
- Mass-Energy Conversion, Mass Defect and Nuclear Binding Energy 7:44
- Fusion, Fission, Carbon Dating, Tracers & Imaging: Applications of Nuclear Chemistry 6:41
- Disintegration Energy in Nuclear Physics: Definition & Formula 5:40
- Atomic Mass Unit (AMU): Definition, Standard & Conversion 6:00
- Go to Physical Science - Atomic and Nuclear Physics: Homework Help

- Computer Science 335: Mobile Forensics
- Electricity, Physics & Engineering Lesson Plans
- Teaching Economics Lesson Plans
- U.S. Politics & Civics Lesson Plans
- US History - Civil War: Lesson Plans & Resources
- HESI Admission Assessment Exam: Factors & Multiples
- HESI Admission Assessment Exam: Probability, Ratios & Proportions
- HESI Admission Assessment Exam: 3D Shapes
- HESI Admission Assessment Exam: Punctuation
- HESI Admission Assessment Exam: Linear Equations, Inequalities & Functions
- CPCE Prep Product Comparison
- CCXP Prep Product Comparison
- CNE Prep Product Comparison
- IAAP CAP Prep Product Comparison
- TACHS Prep Product Comparison
- Top 50 Blended Learning High Schools
- EPPP Prep Product Comparison

- History of Sparta
- Realistic vs Optimistic Thinking
- How Language Reflects Culture & Affects Meaning
- Logical Thinking & Reasoning Questions: Lesson for Kids
- Exceptions to the Octet Rule in Chemistry
- Database Hacking: Attack Types & Defenses
- Pride and Prejudice Discussion Questions
- Quiz & Worksheet - Frontalis Muscle
- Quiz & Worksheet - Dolphin Mating & Reproduction
- Octopus Diet: Quiz & Worksheet for Kids
- Quiz & Worksheet - Fezziwig in A Christmas Carol
- Flashcards - Measurement & Experimental Design
- Flashcards - Stars & Celestial Bodies
- Kindergarten Math Worksheets & Printables
- ESL Conversation Questions & Topics for ESL Students

- Philosophy 102: Ethics in America
- Business 306: Strategic Human Resources Management
- UExcel Contemporary Mathematics: Study Guide & Test Prep
- AQA A-Level Chemistry: Practice and Study Guide
- Science Standards Information for Teachers
- NMTA Middle Grades Math: Percents
- Holt McDougal Modern Chemistry Chapter 19: Oxidation and Reduction Reactions
- Quiz & Worksheet - What Is Prior Knowledge?
- Quiz & Worksheet - Features of Representative Governments
- Quiz & Worksheet - Comparing Utopias & Dystopias
- Quiz & Worksheet - Anatomy of a Lymph
- Quiz & Worksheet - Elements of an Ecosystem

- Fathers & Sons: Summary & Author
- Beowulf Literary Criticism & Critical Analysis
- 5th Grade Science Standards in California
- Common Core State Standards in Colorado
- Common Core State Standards in Maryland
- Nevada State Science Standards
- Best Way to Learn Spanish On Your Own
- South Dakota State Standards for Social Studies
- Homeschooling in Australia
- National Science Standards for High School
- Homeschooling in Michigan
- Causes & Effects of the Vietnam War: Assignment 1 - President Johnson & Guerilla Warfare

- Tech and Engineering - Videos
- Tech and Engineering - Quizzes
- Tech and Engineering - Questions & Answers

Browse by subject