Understanding Atomic Mass Units

This lesson delves into atomic mass units (AMU), explaining their basis on the carbon-12 atom. It covers the concept of relative isotopic mass, using helium as an example, and discusses the historical context of choosing carbon-12 as the reference atom. The lesson also includes a practical exercise with nitrogen to reinforce understanding. Key takeaways include the definition of AMU as 1/12th of a carbon-12 atom's mass and the method to calculate atomic mass for different elements.

What must you understand before learning about atomic mass units?

• The periodic table

• The history of chemistry

• The parts of an atom and mass number

• Chemical reactions

What is the mass number of a helium atom?

• 2

• 4

• 6

• 8

What is the reference atom for measuring atomic mass units?

• Carbon-12

• Helium

• Oxygen-16

• Hydrogen

How is one atomic mass unit (AMU) defined?

• 1/4th of the mass of a helium atom

• 1/10th of the mass of a hydrogen atom

• 1/16th of the mass of an oxygen atom

• 1/12th of the mass of a carbon-12 atom

What is the relative isotopic mass of a hydrogen atom?

• 14

• 12

• 2

• 1

What is the relative isotopic mass of a fluorine atom?

• 24

• 19

• 14

• 9

What is the mass number of a nitrogen atom?

• 19

• 16

• 7

• 14

Why are not all atomic masses whole numbers?

• Due to isotopes

• Due to chemical reactions

• Because of measurement errors

• Because atoms are unstable

What is the significance of the carbon-12 atom in atomic mass units?

• It is used as a reference for AMU

• It is the most abundant element

• It is the lightest element

• It has the highest atomic number

What should you remember from this lesson about atomic mass units?

• AMU is based on hydrogen

• AMU is 1/12th of the mass of a carbon-12 atom

• AMU is a random measurement

• AMU is the same for all elements