Lecture Notes: Chemistry - Atomic Symbols, Isotopes, and Atomic Mass

Introduction to Nuclear Symbols

• Atomic Number (Z): Number of protons in the nucleus.
• Mass Number (A): Number of protons + number of neutrons.
• Isotopes: Atoms of the same element (same Z) but different numbers of neutrons.
• Nuclear Symbol Notation:
  • A over Z next to the element symbol X.
  • Example: Hydrogen isotopes - Hydrogen-1, Deuterium (Hydrogen-2), Tritium (Hydrogen-3).

Naming Isotopes and Nuclear Applications

• Isotopes are named by the element followed by a dash and the mass number, e.g., Uranium-235.
• Usage of Uranium-235 in nuclear power and weapons.

Symbol Notation and Charges

• Notation:
  • Mass number (A) at upper left.
  • Atomic number (Z) at lower left.
  • Charge at upper right.
• Charge Calculation:
  • Charge = Number of protons - Number of electrons.
  • Examples: For neutral atoms, protons = electrons; for ions, adjust electrons based on charge.
• Benjamin Franklin's Contribution: Defined electrons as negatively charged, impacting notation.

Protons, Neutrons, and Electrons

• Calculating Neutrons: Mass number - Atomic number.
• Neutral Atoms: Protons = Electrons.
• Anions: More electrons than protons.
• Cations: Fewer electrons than protons.

Examples and Practice Problems

• Given symbols, determine protons, neutrons, electrons.
• Oxygen Example: Mass number 16, atomic number 8 (neutral atom).
  • Neutrons = 8, Electrons = 8 (or 10 if -2 charge).
• Cesium Ion Example: Atomic number 55, mass number 133, +1 charge.
• Fluorine Use: In medical diagnostics, e.g., fluoroscopes.

Atomic Mass and Weighted Averages

• Atomic Mass: Protons + Neutrons but periodic table shows weighted averages.
• Weighted Average Calculation:
  • Consider isotope masses and natural abundance.
  • Use mass spectrometry for accurate measurement.
• Example: Carbon in the body mostly Carbon-12, slight Carbon-13.

Mass Spectrometry and Applications

• Mass Spectrometry: Ionizes atoms, measures mass for identifying atomic/molecular masses.
• Weighted Average Example: Lithium isotopes (Lithium-6 and Lithium-7) lead to average atomic mass on the periodic table.
• Applications: Used for environmental samples in water, soil, air (size limitations apply).

Conclusion

• Understanding Atomic Mass: Understanding isotopes and their abundance helps explain atomic mass values on the periodic table.
• Practical Uses: Identifies elements and compounds, significant in both chemical education and practical applications like environmental testing.

This covers the key concepts discussed in the section, ensuring you understand how nuclear symbols are used, how to calculate properties of atoms and ions, and the importance of isotopes and atomic masses.