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.