Understanding Atomic Mass Units

This lesson delves into atomic mass units, 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 standard reference. The video includes a practical exercise with nitrogen and introduces the concept of non-whole atomic masses, setting the stage for further exploration in subsequent lessons.

What must you understand before learning about atomic mass units?

• The history of chemistry

• The periodic table

• Chemical reactions

• The parts of an atom and mass number

What is the mass number of a helium atom?

• 2

• 6

• 8

• 4

What was the first element used as a reference for atomic mass?

• Hydrogen

• Carbon

• Oxygen

• Nitrogen

Which atom is currently used as the standard for atomic mass units?

• Helium-4

• Hydrogen-1

• Oxygen-16

• Carbon-12

How is one atomic mass unit 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?

• 2

• 1

• 12

• 4

What is the relative isotopic mass of a fluorine atom?

• 9

• 14

• 24

• 19

What is the mass number of a nitrogen atom?

• 21

• 7

• 14

• 28

Why are atomic masses not always whole numbers?

• Due to changes in atomic structure

• Because of isotopic variations

• Due to rounding errors

• Because of measurement inaccuracies

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

• They are always whole numbers

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

• They are used to measure volume

• They are based on hydrogen