In-depth Notes on Atomic Structure and the Periodic Table

5.1 Evolution of the Atomic Model

• John Dalton's Atomic Theory

  • Described all matter as composed of atoms, which are small, indivisible particles.

• Joseph John Thomson

  • Discovered negatively charged particles (electrons).
  • Proposed the "plum pudding" model, where electrons are distributed throughout a positively charged mass.

• Ernest Rutherford

  • Conducted the gold foil experiment, revealing that atoms consist mostly of empty space with a dense, positively charged nucleus.
  • Identified protons and neutrons as constituents of the nucleus.

• Neils Bohr

  • Revised Rutherford’s model by suggesting that electrons reside in specific energy levels around the nucleus.

5.2 The Structure of the Atom

• Atoms consist of:

  • Protons: Positively charged.
  • Neutrons: Neutral particles (no charge).
  • Electrons: Negatively charged.

• Atomic Number:

  • Number of protons; unique to each element.
  • Always a whole number.

• Mass Number:

  • Sum of protons and neutrons; also a whole number.

• Nucleus:

  • Contains protons and neutrons, accounting for most atomic mass.

• Energy Levels:

  • Electrons occupy energy levels outside the nucleus.

• Isotopes:

  • Atoms of the same element with the same number of protons but different neutron counts.

5.3 The Periodic Table

• Modern Periodic Table:

  • Organized by increasing atomic number, with periodic repetition in element properties.

• Metals vs. Non-metals:

  • Metals: Shiny, solids at room temperature, good conductors of heat/electricity, malleable, ductile.
  • Non-metals: Usually gases or brittle solids, poor conductors, not shiny.
  • Metalloids: Exhibit characteristics of both metals and non-metals.

• Environmental Impact:

  • Metal poisoning (e.g., mercury) in the environment can severely affect health and practices of local communities, such as Aboriginal peoples.

• Table Structure:

  • Periods: Horizontal rows.
  • Groups (Families): Vertical columns.

• Key elements groups: alkali metals, alkaline-earth metals, halogens, noble gases.

5.4 Trends in the Periodic Table

• Element Properties Trends:

  • Affected by electron arrangement within atoms.

• Valence Electrons:

  • Determine many properties; count of valence electrons is consistent within a group and varies across a period.

• Noble Gases:

  • Non-reactive due to full valence electron shells.

• Atomic Size Trends:

  • Increases down a group and from right to left across a period in the periodic table.