Lecture on Isotopes and Ions

Basic Concepts of Atoms

• Atoms consist of:
  • Protons: Carry a +1 charge
  • Neutrons: Neutral charge
  • Electrons: Carry a -1 charge
• Neutral Atom: Number of protons = Number of electrons.

Atomic Number and Mass Number

• Atomic Number:
  • Equals the number of protons in the nucleus.
  • Identifies the element.
• Mass Number:
  • Equals the total number of protons and neutrons.

Representation of Elements

• Symbol notation:
  • Element Symbol (X)
  • Atomic number as subscript (lower left)
  • Mass number as superscript (upper left)

Isotopes

• Definition: Atoms of the same element (same number of protons) but different numbers of neutrons.
• Example:
  • Hydrogen isotopes:
    • Protium: 1 proton, 0 neutrons, Mass number = 1
    • Deuterium: 1 proton, 1 neutron, Mass number = 2
    • Tritium: 1 proton, 2 neutrons, Mass number = 3
• Isotope notation:
  • Protium: H-1 or Hydrogen-1
  • Deuterium: H-2 or Hydrogen-2
  • Tritium: H-3 or Hydrogen-3

Ions

• Definition: Atoms or groups of atoms with an overall charge (positive or negative).
• Formation of ions:
  • Occurs through gaining or losing electrons.

Types of Ions

• Cations: Positive charge

  • Example: Sodium (Na):
    • Neutral sodium has 11 protons and 11 electrons.
    • Sodium loses an electron, resulting in Na⁺ (11 protons, 10 electrons).

• Anions: Negative charge

  • Example: Chlorine (Cl):
    • Neutral chlorine has 17 protons and 17 electrons.
    • Chlorine gains an electron, resulting in Cl⁻ (17 protons, 18 electrons).

Sample Problems

• Problem 1: Uranium-235

  • Mass number = 235
  • Atomic number = 92 (number of protons)
  • Neutrons = 235 - 92 = 143
  • Electrons = 92 (for neutral atom)

• Problem 2: Neutral Isotope

  • Given: 54 electrons, 79 neutrons
  • Protons = 54 (number of electrons for neutrality)
  • Element = Xenon (Xe)
  • Mass number = 54 + 79 = 133
  • Notation: Xe-133 or Xenon-133

Participation Questions

1. Isotope of Magnesium with a given mass number and a +2 charge.
2. Identify isotope with 27 protons and 32 neutrons.

Additional Notes

• Contact the instructor for further questions or clarifications.