Test Your Knowledge
Key Idea 4: Atomic Weight Intervals and
the IUPAC Periodic Table of the Elements and Isotopes
19) What is the rationale for using interval atomic weight values?
- Varying relative abundances of isotopes
- Varying atomic masses of isotopes
- Varying numbers of electrons in isotopes of an element
- Varying measurement techniques
20) The atomic weight of hydrogen is expressed as [1.00784, 1.00811]. What does this mean?
- The atomic weight of hydrogen is either 1.00784 or 1.00811
- The atomic mass of the most abundant isotope of hydrogen is 1.00811 and the atomic mass of the least abundant isotope is 1.00784
- The atomic weight of hydrogen varies in normal materials and can be as low as 1.00784 to as high as 1.00811
- The atomic weight of hydrogen is the difference between 1.00784 and 1.00811
21) Taking it Further: Carbon is an example of an element that has been assigned an atomic weight interval. The variation in the relative abundance of carbon isotopes has many practical applications. Open the Isotope Ratio Mass Spectrometry Learning Tool and answer one of the following questions in a short summary paragraph.
- How can 400,000 years of temperature data be determined from ice core samples?
- How is synthetic testosterone detected in professional athletes?
- How can you tell if your honey has been diluted with sugar syrup?
- How do scientists discover the sources of methane molecules on Earth and Mars?
22) If an element is found to have only 1 stable isotope or 1 relatively abundant, long-lived radioisotope, can its atomic weight be expressed as an atomic weight interval?
- Yes – atomic weights of all elements can be expressed as atomic weight intervals
- Yes – the relative atomic mass of the isotope can vary in normal materials, thereby causing the atomic weight to vary
- Yes – the relative abundance of the isotope can vary in normal materials
- No – in order for the atomic weight of an element to vary, the isotopic composition of the element must vary and if there is only one isotope, the isotopic composition is invariant
23) The IUPAC Periodic Table of the Elements and Isotopes categorizes elements based on characteristics of their standard atomic weights. Write a short summary sentence that describes each of the four categories.
- Pink
- Blue
- Yellow
- White