Starter quiz
- What do isotopes of an element have in common?
- Same atomic mass
- Same number of neutrons
- Same number of protons ✓
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- Atoms form ______ when they gain or lose electrons.
- 'ions' ✓
- How do you calculate the number of neutrons in an atom?
- Atomic number - Mass number
- Mass number + Atomic number
- Mass number - Atomic number ✓
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- Which subatomic particle determines the identity of an element?
- Electron
- Neutron
- Proton ✓
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- What does the relative atomic mass of an element represent?
- The total mass of an element's isotopes combined.
- An average value that takes account of the abundance of the isotopes. ✓
- The mass of the most abundant isotope of an element.
- The mass of one mole of the element in grams.
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- What is the relative atomic mass of chlorine, given isotopes Cl-35 (75%) and Cl-37 (25%)?
- '35.5' ✓
Exit quiz
- What does the M⁺ peak represent in a mass spectrum?
- The base peak
- The heaviest fragment
- The molecular ion ✓
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- What does fragmentation in mass spectrometry help identify?
- Atomic number
- Electron configuration
- Molecular structure ✓
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- How is the relative atomic mass calculated using mass spectrometry data?
- Counting the total number of isotopes
- Using the atomic number
- (mass of isotope 1 × abundance) + (mass of isotope 2 × abundance)/100 ✓
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- What is a molecular ion?
- A molecule with an unequal number of protons and neutrons.
- A molecule that has formed a covalent bond.
- An ion produced when the molecule is ionised by loss of an electron. ✓
- A neutral molecule with no charge.
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- Calculate the relative atomic mass of bromine, given isotopes Br-79 (50.7%) and Br-81 (49.3%). Give your answer to one decimal place.
- '79.9' ✓
- Calculate the relative atomic mass of neon, given isotopes Ne-20 (90.48%), Ne-21 (0.27%), Ne-22 (9.25%). Give your answer to two decimal places.
- '20.22' ✓
Worksheet
Presentation
Video
Lesson Details
Key learning points
- Isotopes are atoms of the same element with different numbers of neutrons.
- Relative abundances of isotopes can be used to calculate the relative atomic mass (RAM) of an element.
- Mass spectrometry ionises samples to create positive ions for analysis.
- The M⁺ peak represents the molecular ion, indicating the molecular mass.
- Fragmentation in mass spectrometry helps identify molecular structure by breaking molecules into smaller ions.
Common misconception
All peaks in a mass spectrum represent intact (and neutral) molecules or atoms.
Clarify that in mass spectrometry, all detected peaks represent ionised species, not neutral molecules or atoms. The peaks can correspond to either the molecular ion (M⁺) or smaller ionised fragments, as well as different isotopes of an element.
Keywords
Isotope - An atom of an element with the same number of protons, but different number of neutrons.
Relative atomic mass - An average value that takes account of the abundance of the isotopes of the element.
Molecular mass - The sum of the atomic masses of all the atoms in a molecule.
Molecular ion - The ion produced when the molecule is ionised by loss of an electron from the molecule.
Spectrometer - An apparatus used for recording and measuring spectra, especially as a method of analysis.