Lecture Notes: Atomic Structure and Isotopes

Structure of an Atom

• An atom consists of:
  • Central Nucleus: Composed of protons and neutrons.
  • Electrons: Orbit around the nucleus.

Element Identification

• Number of Protons: Determines the element.
• Hydrogen: Smallest element with one proton and one electron.
• Helium: Two protons, two neutrons, and two electrons.

Periodic Table

• Elements: Around 100 different elements organized into the periodic table.
• Nuclear Symbols: Boxes on the periodic table representing elements.
  • Atomic Number: Located bottom left of the symbol, represents the number of protons.
  • Element Symbols: One or two-letter representation (e.g., C for Carbon, Li for Lithium).
  • Some symbols may not match the English name (e.g., Na for Sodium, Fe for Iron).

Isotopes

• Definition: Different forms of the same element that have the same number of protons but different numbers of neutrons.
• Carbon Isotopes:
  • Carbon-12: 6 protons, 6 neutrons, 6 electrons.
  • Carbon-13: 6 protons, 7 neutrons, 6 electrons.
• Chemical Properties: Isotopes behave chemically the same way.

Relative Atomic Mass (Ar)

• Definition: The average mass of all isotopes of an element.
• Calculation:
  • Use the formula: [ \text{Relative Atomic Mass} = \frac{\sum (\text{isotope abundance} \times \text{isotope mass})}{\sum \text{abundances of all isotopes}} ]
• Example: Copper
  • Stable Isotopes:
    • Copper-63: 69.2% abundance.
    • Copper-65: 30.8% abundance.
  • Calculation Steps:
    1. Multiply each isotope's abundance by its mass:
       • Copper-63: 69.2 x 63 = 4359.6.
       • Copper-65: 30.8 x 65 = 2002.
    2. Add these products: 4359.6 + 2002 = 6361.6.
    3. Divide by total abundances: ( \frac{6361.6}{100} = 63.6169 ).
    4. Round to one decimal place: 63.6.
  • Result: Relative atomic mass of copper is 63.6.

Notes: Share insights or comments for further discussion.