Periodic Trends and Structure of the Periodic Table

Structure of the Periodic Table

  • The Periodic Table has rows (called Periods) and columns (called Groups or Families).

  • Elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell.

  • Elements in the same period have the same number of electron shells, which affects how they react and bond with other elements.

Classification of Elements

  • Metals: Good at conducting heat and electricity, can be shaped easily, and look shiny. Examples: Iron (Fe), Copper (Cu).

  • Nonmetals: Poor conductors of heat and electricity, usually brittle when solid, can be gases or liquids at room temperature. Examples: Oxygen (O), Sulfur (S).

  • Metalloids: Share properties of metals and nonmetals. Examples: Silicon (Si), Arsenic (As), used in electronics.

Key Periodic Trends

  • Atomic Radius:

    • Across a period: Atoms get smaller because the positive charge in the nucleus pulls electrons in.

    • Down a group: Atoms get bigger as more electron shells are added.

  • Ionization Energy:

    • Across a period: It becomes harder to remove an electron because of the increasing positive charge.

    • Down a group: It gets easier to remove an electron because they are farther from the nucleus.

  • Electron Affinity:

    • Across a period: Atoms want to gain electrons more as they get closer to having a full outer shell.

    • Down a group: Atoms want to gain electrons less because the new electrons are farther from the nucleus.

  • Electronegativity:

    • Across a period: Atoms get better at attracting electrons as they need to fill their outer shell.

    • Down a group: Atoms get less able to attract electrons as they get larger.

Special Groups of Elements

  • Alkali Metals (Group 1): Very reactive, especially with water, and have one electron in their outer shell. Example: Sodium (Na).

  • Alkaline Earth Metals (Group 2): Reactive but not as much as alkali metals, have two electrons in their outer shell. Example: Magnesium (Mg).

  • Transition Metals (Groups 3-12): Less reactive, can form colorful compounds, and have different ways to bond. Examples: Iron (Fe), Copper (Cu).

  • Halogens (Group 17): Very reactive nonmetals with seven valence electrons, make salts with metals. Example: Chlorine (Cl).

  • Noble Gases (Group 18): Very stable and do not react because they have a full outer shell. Example: Neon (Ne).

Trends in Metallic vs. Non-metallic Properties

  • Metallic Character:

    • Across a period: Metals change to nonmetals as you go left to right.

    • Down a group: Metals become more like metals.

  • Non-metallic Character:

    • Across a period: Nonmetals become more like nonmetals.

    • Down a group: Nonmetals become less like nonmetals.