The periodic table | Atoms, elements, and the periodic table | High school chemistry | Khan Academy

Periodic Table Overview

  • The periodic table organizes elements into groups and periods.

  • Elements are arranged in vertical columns called groups and horizontal rows called periods.

Groups

  • Group numbering: Vertical columns numbered 1-18.

    • 1: Group 1 (1A) -> Alkali Metals (e.g., Lithium, Sodium, Potassium)

    • 2: Group 2 (2A) -> Alkaline Earth Metals (e.g., Magnesium, Calcium)

    • Group 3-12: Transition Metals (general category)

    • Group 13-18: Various nonmetals and metalloids.

  • Alternative Group numbering: A notation emphasizing valence electrons:

    • Group 1A -> Group 1; 2A -> Group 2; skips to 3A through 8A after group 2, focusing on main group elements.

Periods

  • A period represents a horizontal row in the periodic table.

    • Period 1: Hydrogen, Helium.

    • Period 2: Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, Neon.

    • Periods continue with numbers 3-6.

Metals

Alkali Metals

  • Found in Group 1 (1A) - soft, silvery metals, very reactive.

    • Common alkali metals: Lithium, Sodium, Potassium.

    • Highly reactive with water, never found in pure form in nature.

    • Hydrogen is in Group 1 but is a nonmetal, often highlighted as an exception.

Alkaline Earth Metals

  • Found in Group 2 (2A) - also reactive, but less so than alkali metals.

    • Includes: Magnesium, Calcium, Strontium.

    • Found combined with other elements in nature.

General Metal Properties

  • Metals are normally solid (except Mercury).

  • Characteristics:

    • Malleable: Can be shaped and formed easily.

    • Ductile: Can be drawn into wires (e.g., Copper).

    • Good conductors of heat and electricity.

Nonmetals

Halogens

  • Found in Group 7A (17) - known for being very reactive.

    • Includes: Fluorine, Chlorine, Bromine.

    • Known for colorful and corrosive nature, "salt-formers".

Noble Gases

  • Found in Group 8A (18) - colorless, generally very unreactive gases.

    • Includes: Helium, Neon, Argon, Krypton.

Dividing Line in Periodic Table

  • Left side contains metals, right side contains nonmetals.

  • The zigzag line on the periodic table serves as the boundary.

Metalloids

  • Properties are intermediate between metals and nonmetals.

    • Examples: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, Astatine.

    • Silicon is specifically noted for its semiconductor properties.

Conclusion

  • Understanding the organization of the periodic table assists with recognizing element properties and behaviors.

  • Future discussions will explore electronic structure and transition metals.