How to Convert Grams to Amu

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  • 0:00 Choosing Units Of Measurement
  • 0:42 What Are Atoms?
  • 1:10 Describing The Mass Of Atoms
  • 2:18 Finding An AMU
  • 3:04 AMU Conversions
  • 4:52 Lesson Summary
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Lesson Transcript
Instructor: Catherine Hagandora

Catherine has a doctorate in bioengineering.

This lesson explains the concept of the Atomic Mass Unit (AMU). The definition and significance of the unit is explained. The lesson also uses examples to describe how to convert from grams to AMU.

Choosing Units of Measurement

What is the price of a new car - $25,000 or 2,500,000 pennies? What does the recipe call for - a teaspoon of milk or two hundredths of a cup of milk?

Different units of measurement are used to describe different quantities. When a recipe calls for a small quantity of milk, it is easier to measure it in teaspoons than in cups. It is also easier to think about how much a car is worth in dollars than in pennies. These units make their respective quantities easier to understand and apply. Scientists use the same principle when describing the mass of atoms.

What Are Atoms?

Elements are pure substances that cannot be chemically divided into other substances. Just a few examples of elements include silver, iodine, carbon, and sodium. The smallest possible piece of an element is an atom. Different atoms have different masses depending on their number of protons, neutrons, and electrons. For example, a sodium atom has 11 protons, 11 electrons, and 12 neutrons.

Describing the Mass of Atoms

Atoms are so small that even a single fleck of dust contains about ten quadrillion atoms (think of a million times a billion). So, just like it is not very practical to describe the price of a car in pennies, it is even less practical to describe the mass of an atom in grams. In fact, when scientists wanted to make it very easy to describe different quantities of atoms, they had to come up with a whole new unit; this is where the atomic mass unit, or AMU, comes in.

The AMU is defined as 1/12 the mass of a carbon atom with six neutrons, six electrons, and six protons. Because the mass of an electron is close to nothing, defining an AMU this way makes the mass of one proton equal to one AMU and the mass of one neutron equal to one AMU. Since there are no partial protons or neutrons in an atom, this means that the atomic mass of every atom is close to (but not quite) a whole number. This turns out to be a very convenient way of describing the masses of atoms.

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