Isotopes and Mass Spectrometry

Key Concepts

• Isotopes: Atoms with the same number of protons but different numbers of neutrons.
• Relative Abundance: Percentage of atoms with a specific atomic mass in a sample.
• Average Atomic Mass: A weighted average of an element's isotopes' atomic masses based on their relative abundances.

Introduction to Atomic Structure

• Atoms consist of three main subatomic particles:
  • Protons: Positive charge, located in the nucleus.
  • Neutrons: No charge, located in the nucleus.
  • Electrons: Negative charge, orbit around the nucleus.
• Protons and neutrons are bound together in the nucleus by the nuclear strong force.

Isotopes

• Isotopes occupy the same position on the periodic table but have different atomic masses due to differing numbers of neutrons.
• Example: Helium typically has two protons, two neutrons, and two electrons.

Mass and Measurement

• Unified Atomic Mass Unit (u): Allows for mass measurement on an atomic scale.
  • Defined as 1/12 of the mass of a carbon-12 atom.
• Protons and neutrons are about 2000 times more massive than electrons.

Mass Number and Isotope Notation

• Mass Number: Sum of protons and neutrons in an atom's nucleus.
• Isotopic Notation: Displays an isotope's atomic number, mass number, and charge.

Atomic Mass vs. Mass Number

• Atomic Mass: Often nearly the same as mass number but not an integer due to the atomic masses being precise.
• Average Atomic Mass: Calculated from the weighted average of all stable isotopes.

Relative Abundance and Average Atomic Mass

• Example: Chlorine-35 and Chlorine-37 with average atomic mass calculated using their relative abundance.

Mass Spectrometry

• Measures relative abundance and mass-to-charge ratio of ions.
• Mass Spectrometer: Ionizes atoms, deflects ions based on mass-to-charge ratio.
• Mass Spectrum: Graph showing relative abundance vs. m/z ratio.

Analyzing Mass Spectra

• Zirconium example with five naturally occurring isotopes identified via mass spectrometry.
• Spectra show the relative abundance of isotopes.

Summary

• Isotopes vary in neutron number, affecting atomic mass.
• Mass spectrometry is a key tool for identifying isotopes and calculating average atomic mass.
• The importance of mass spectrometry in science extends beyond chemistry, applicable in areas like forensics and space exploration.