CHEMISTRY - Matter - In Depth Atomic Mass Units

The video tutorial explains the concept of atomic mass, focusing on the relative isotopic mass. It uses helium as an example to introduce the mass number and explains how the carbon-12 atom became the standard reference for atomic mass. The tutorial details the calculation of atomic mass using the carbon-12 standard, providing examples with helium, hydrogen, and fluorine. It concludes with a practice exercise on calculating the atomic mass of nitrogen, reinforcing the concept that 1 atomic mass unit is 1/12 of the mass of a carbon-12 atom.

What is the mass number of a helium atom?

• 2

• 4

• 8

• 6

Which atom was agreed upon in 1961 as the reference for atomic mass units?

• Hydrogen

• Oxygen-16

• Carbon-12

• Helium

What fraction of a carbon-12 atom's mass is defined as one atomic mass unit (AMU)?

• 1/20

• 1/10

• 1/12

• 1/16

If a hydrogen atom has a relative isotopic mass of 1, what is the relative isotopic mass of a fluorine atom?

• 9

• 24

• 14

• 19

How do you determine the relative isotopic mass of a nitrogen atom?

• By counting its electrons

• By using its mass number, which is 14

• By comparing it to a hydrogen atom

• By measuring its weight in grams