Relative Atomic Mass | Properties of Matter | Chemistry | FuseSchool

Summary

This video explains the concept of relative isotopic mass, focusing on elements like chlorine, which has isotopes with different masses, such as chlorine-35 and chlorine-37. It distinguishes between isotopic mass and relative atomic mass, emphasizing that the latter is the weighted average of naturally occurring isotopes based on their abundance. For example, chlorine consists of approximately 75% chlorine-35 and 25% chlorine-37. The video illustrates how to calculate relative atomic mass using a sample of 100 chlorine atoms, highlighting the importance of considering the abundance of each isotope to arrive at an accurate average.

Takeaways

• 😀 The relative isotopic mass is defined in relation to carbon-12, highlighting its foundational role in atomic mass calculations.
• 😀 Different isotopes, like chlorine-35 and chlorine-37, have varying masses, which is essential for understanding their properties.
• 😀 The mass number on the periodic table is distinct from the isotopic mass; the former is a whole number, while the latter involves averages.
• 😀 Relative atomic mass is the average mass of naturally occurring isotopes, taking into account their abundance in nature.
• 😀 Chlorine isotopes are not present in equal proportions; 75% of naturally occurring chlorine is chlorine-35, and 25% is chlorine-37.
• 😀 To calculate the average mass of isotopes, a weighted average must be employed rather than a simple arithmetic mean.
• 😀 A practical example shows that in a sample of 100 chlorine atoms, 75 are chlorine-35 and 25 are chlorine-37, leading to specific mass calculations.
• 😀 The total mass of a sample can be calculated by summing the products of the number of atoms and their respective masses.
• 😀 The average mass of a chlorine atom in the example is calculated to be 35.5, closer to the more abundant chlorine-35.
• 😀 Understanding the concept of relative atomic mass is crucial for chemistry as it underpins the behavior and reactivity of elements.

Q & A

What is isotopic mass?

Isotopic mass is the mass of an element's isotopes in relation to a standard, specifically carbon-12.

How does relative atomic mass differ from mass number?

Relative atomic mass is a weighted average of the isotopes based on their natural abundances, while mass number is a whole number representing the total number of protons and neutrons in an atom.

What are the two main isotopes of chlorine mentioned in the script?

The two main isotopes of chlorine discussed are chlorine-35 and chlorine-37.

What percentage of naturally occurring chlorine is chlorine-35?

Approximately 75% of naturally occurring chlorine is chlorine-35.

What is the process for calculating the relative atomic mass of chlorine?

To calculate the relative atomic mass of chlorine, multiply the mass of each isotope by its abundance, sum the results, and then divide by the total number of atoms.

Why do we use a weighted average for calculating relative atomic mass?

A weighted average is used to account for the different natural abundances of each isotope, reflecting their contribution to the overall average mass.

What is the significance of carbon-12 in isotopic mass calculations?

Carbon-12 serves as the standard reference point for measuring isotopic masses and calculating relative atomic masses.

How does the abundance of isotopes affect the calculated relative atomic mass?

The abundance of isotopes influences the calculated relative atomic mass by giving more weight to isotopes that are more prevalent in nature, thus affecting the average.

What is the formula used to calculate the total mass of a sample of chlorine?

The total mass of a sample of chlorine is calculated using the formula: (number of chlorine-35 atoms × 35) + (number of chlorine-37 atoms × 37).

In the example, what is the final relative atomic mass calculated for chlorine?

The final relative atomic mass calculated for chlorine is 35.5, reflecting a weighted average based on its isotopic abundances.