Understanding Atomic Mass and Isotopes

The video tutorial explains why atomic masses on the periodic table are not whole numbers. It introduces isotopes, which are atoms of the same element with different numbers of neutrons, and explains how the relative abundance of isotopes affects the calculation of an element's relative atomic mass. Using chlorine and bromine as examples, the video demonstrates how to calculate the weighted mean atomic mass. The tutorial concludes by emphasizing that the relative atomic mass is a weighted mean of isotopes, explaining why these values are not whole numbers.

Why are atomic masses not always whole numbers?

• Due to the presence of electrons.

• Because atoms are constantly changing.

• Due to errors in measurement.

• Because of the presence of isotopes with different neutron numbers.

What are isotopes?

• Atoms with the same number of protons but different numbers of neutrons.

• Atoms with different numbers of electrons.

• Atoms with different numbers of protons.

• Atoms with the same number of neutrons but different numbers of electrons.

In a sample of chlorine, what is the approximate percentage of chlorine-35?

• 50%

• 100%

• 75%

• 25%

How is the relative atomic mass of an element calculated?

• By considering the most common isotope only.

• By using the weighted mean of isotopes based on their abundance.

• By averaging the masses of all isotopes.

• By adding the masses of protons and neutrons.

What is the relative atomic mass of chlorine?

• 36

• 35.5

• 37

• 35

In the bromine example, what is the relative atomic mass calculated?

• 79

• 80

• 78

• 81

What percentage of bromine-79 is present in the given sample?

• 100%

• 75%

• 25%

• 50%

Why are most relative atomic masses not whole numbers?

• Due to the presence of electrons.

• Because atoms are unstable.

• Because of measurement errors.

• Due to the presence of isotopes with varying abundances.

What does the term 'weighted' mean in the context of atomic mass?

• Using only the mass of protons.

• Considering the mass of the heaviest isotope.

• Taking into account the relative abundance of each isotope.

• Ignoring the less common isotopes.

Where can you learn more about isotopes and atomic mass units?

• In physics classes.

• In chemistry textbooks only.

• In other lessons provided by the same source.

• In the periodic table.