Classifying the Elements

Reading the Periodic Table

  • The periodic table displays:
    • Symbols of the elements
    • Names of the elements
    • Information about the structure of their atoms
  • A square in the periodic table contains:
    • Symbol for the element (e.g., Al for aluminum)
    • Atomic number above the symbol (e.g., 13 for aluminum)
    • Element name and atomic mass below the symbol
    • Vertical column indicating the number of electrons in each occupied energy level (e.g., 2, 8, 3 for aluminum)
  • Element symbols are color-coded to indicate their state at room temperature:
    • Black: Solid
    • Red: Gas
    • Blue: Liquid (mercury and bromine)
    • Gray: Not found in nature
  • Background colors distinguish groups of elements.
    • Orange shades are used for metals in Groups 1A and 2A.
      • Group 1A: Alkali metals
      • Group 2A: Alkaline earth metals
    • Group 7A: Halogens
      • Halogen is derived from Greek 'hals' (salt) and Latin 'genesis' (to be born).

Electron Configurations in Groups

  • Elements can be classified based on electron configurations into:
    • Noble gases
    • Representative elements
    • Transition metals
    • Inner transition metals

Noble Gases

  • Located in Group 8A.
  • Examples: Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr)
  • Also known as inert gases because they rarely react.
  • Electron configurations:
    • Helium (He): 1s^2
    • Neon (Ne): 1s^22s^22p^6
    • Argon (Ar): 1s^22s^22p^63s^23p^6
    • Krypton (Kr): 1s^22s^22p^63s^23p^63d^{10}4s^24p^6
  • The s and p sublevels are completely filled with electrons (2 in s and 6 in p).

Representative Elements

  • Include elements in Groups 1A through 7A.
  • Display a wide range of physical and chemical properties.
  • Can be metals, nonmetals, or metalloids.
  • Mostly solids, some gases, and one liquid (bromine) at room temperature.
  • The s and p sublevels of the highest occupied energy level are not filled.
  • Examples:
    • Lithium (Li): 1s^22s^1
    • Carbon (C): 1s^22s^22p^2
    • Silicon (Si): 1s^22s^22p^63s^23p^2
  • The group number equals the number of electrons in the highest occupied energy level.

Transition Elements

  • Located in the B groups of the periodic table, separating the A groups.
  • Two types: transition metals and inner transition metals

Transition Metals

  • Usually displayed in the main body of the periodic table.
  • Examples: Copper (Cu), Silver (Ag), Gold (Au), Iron (Fe)
  • The highest occupied s sublevel and a nearby d sublevel contain electrons.
  • Characterized by the presence of electrons in d orbitals.

Inner Transition Metals

  • Appear below the main body of the periodic table.
  • The highest occupied s sublevel and a nearby f sublevel generally contain electrons.
  • Characterized by the presence of electrons in f orbitals.
  • Example: Uranium (U)
  • Formerly referred to as rare-earth elements (misleading name).
  • Some are not found in nature and are prepared in laboratories.

Blocks of Elements

  • The periodic table is divided into blocks corresponding to the highest occupied sublevels.
    • s block: Groups 1A and 2A and helium.
    • p block: Groups 3A, 4A, 5A, 6A, 7A, and 8A (except helium).
    • d block: Transition metals.
    • f block: Inner transition metals.
  • Each period corresponds to a principal energy level.
  • For elements in Period 3:
    • s and p sublevels in energy levels 1 and 2 are filled.
    • Read across Period 3 from left to right to complete the configuration.
  • For transition elements, electrons are added to a d sublevel with a principal energy level one less than the period number.
  • For inner transition metals, the principal energy level of the f sublevel is two less than the period number.

Sample Problem: Electron Configuration of Nickel (Ni)

  • Nickel is located in the fourth period and has 28 electrons.
  • Full electron configuration: 1s^22s^22p^63s^23p^63d^84s^2
  • The period indicates the highest occupied principal energy level.
  • The group number indicates the number of electrons in the highest occupied energy level.

Key Concepts

  • Periodic tables display element symbols, names, atomic numbers, atomic masses, and electron configurations.
  • Elements are sorted into noble gases, representative elements, transition metals, and inner transition metals based on electron configurations.

Glossary Terms

  • Alkali metal: Group 1A
  • Alkaline earth metal: Group 2A
  • Halogen: Group 7A
  • Noble gas: Group 8A; filled s and p sublevels in the highest occupied energy level
  • Representative element: An “A” group element with partially filled s and p sublevels in the highest occupied energy level
  • Transition metal: Group B element with electrons in the highest occupied s sublevel and a nearby d sublevel
  • Inner transition metal: Lanthanide or actinide series element with electrons in the highest occupied s sublevel and a nearby f sublevel