Lecture Notes on Atoms and Elements

Introduction to Atomic Theory

• Dalton's Atomic Theory (Early 1800s)
  • Key Points: All matter is made of atoms; atoms are indivisible and indestructible.
  • Correction: Atoms can be divided into subatomic particles (electrons, protons, neutrons).
  • Isotopes: Atoms of the same element can differ in mass and properties due to the existence of isotopes.

Dalton's Atomic Theory Detailed

1. All matter is made of atoms: True.
2. Atoms are indivisible and indestructible: Incorrect, can be broken down further.
3. All atoms of a given element are identical: Incorrect, due to isotopes.
4. Compounds are combinations of different elements: True.
5. Chemical reactions are the rearrangement of atoms: True.

Discovery of Subatomic Particles

• Electron (Around 1900): First discovered subatomic particle, part of the atom, negatively charged.
• Protons and Neutrons: Found in the nucleus, protons are positively charged, neutrons are neutral.

Alpha Scattering Experiment (1910)

• Purpose: Test the plum pudding model (positive charge spread out with electrons embedded).
• Result: Disproved the model, leading to the discovery of the nucleus.
• Nucleus: Dense central core, contains protons and neutrons.

Structure of the Atom

• Nucleus: Contains protons and neutrons, dense.
• Electrons: Negatively charged, orbit the nucleus.
• Mass and Charge:
  • Electrons are much lighter (~1/1000 of a proton's mass).
  • Most of the atom's mass is in the nucleus.
  • Atoms are mostly empty space.

Isotopes

• Definition: Atoms of the same element with different numbers of neutrons.
• Example: Carbon-12 vs Carbon-13.
• Mass Number (A): Sum of protons and neutrons.
• Atomic Number (Z): Number of protons.
• Notation: ( \text{Element}^{A}_{Z} )

Atomic Mass and Units

• Atomic Mass Unit (amu): Defined as 1/12 of the mass of ( ^{12}C ).
• Weighted Average: Used to calculate the atomic mass based on natural isotopic abundance.
• Calculations:
  • Weighted average example with carbon isotopes.
  • Calculation for naturally occurring elements reflects periodic table values.

Key Concepts Review

• Protons define the element.
• Electrons determine chemical behavior.
• Isotopes affect atomic mass.
• Periodic Table Mass: Reflects weighted average of isotopic masses.

Conclusion

• Understanding the structure of atoms, isotope distribution, and atomic mass is crucial for comprehending chemical behavior and properties of elements.