9701 · 1.2
Isotopes flashcards
Revision flashcards for Cambridge 9701 Isotopes (syllabus 1.2). Flip, recall, then mark a real past-paper question.
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What is the definition of an isotope?
Atoms of the same element (same number of protons) with different numbers of neutrons (and therefore different mass numbers).
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Which subatomic particles are the same in isotopes of a single element?
The number of protons and, in a neutral atom, the number of electrons.
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Which subatomic particle differs between isotopes of a single element?
The number of neutrons.
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Why do isotopes of an element have the same chemical properties?
Because they have the same number of electrons in their outer shell (same electron configuration), which determines chemical reactivity.
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Why might isotopes of an element have different physical properties?
Because they have different masses. This can lead to slight differences in properties like density, boiling point, and rate of diffusion.
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What is the full notation for the isotope of chlorine with a mass number of 37?
$^{37}_{17}\text{Cl}$. It has 17 protons, 17 electrons (in a neutral atom), and 37 - 17 = 20 neutrons.
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Define relative atomic mass, $A_r$.
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.
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What does the term 'weighted mean' signify in the calculation of $A_r$?
It means the abundance (or percentage) of each isotope is taken into account. More abundant isotopes contribute more to the final average.
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What is a mass spectrometer used for in the context of isotopes?
To determine the relative isotopic masses and the relative abundances of the isotopes of an element.
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What is a radioisotope?
An isotope with an unstable nucleus that undergoes radioactive decay to become more stable, emitting radiation in the process. For example, carbon-14.
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Exam Trap: Is the mass number on the periodic table?
No. The periodic table shows the relative atomic mass ($A_r$), which is a weighted average. The mass number (A) is an integer for a single isotope nucleus and is not shown on the periodic table.
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How do you calculate the number of neutrons in an isotope like Uranium-235 ($^{235}_{92}\text{U}$)?
Subtract the atomic number (protons) from the mass number (protons + neutrons). Neutrons = 235 - 92 = 143.