Organization of the Periodic Table

The periodic table is organized into rows called periods and columns called groups (or families).

• Periods:

  • Horizontal rows on the periodic table.

  • There are seven periods in total, each representing an increasing number of electron shells.

• Groups:

  • Vertical columns on the periodic table.

  • Elements within the same group share similar chemical properties due to having the same number of valence electrons.

  • Commonly recognized groups include:

    • Group 1: Alkali metals (e.g., lithium, sodium, potassium)

    • Group 2: Alkaline earth metals (e.g., beryllium, magnesium, calcium)

    • Group 17: Halogens (e.g., fluorine, chlorine, bromine)

    • Group 18: Noble gases (e.g., helium, neon, argon)

Periodic Table Trends

1. Atomic Radius

   • The atomic radius is the distance from the nucleus of an atom to the outermost shell of electrons.

   • Trend: The atomic radius generally decreases across a period from left to right and increases down a group.

     • Explanation:

       • As you move across a period, increasing nuclear charge pulls electrons closer, reducing the atomic size.

       • Moving down a group adds electron shells, increasing the distance from the nucleus.

2. Ionization Energy

   • Ionization energy is the energy required to remove an electron from an atom in its gaseous state.

   • Trend: Ionization energy generally increases across a period and decreases down a group.

     • Explanation:

       • Across a period, increased nuclear charge strengthens the attraction between the nucleus and electrons, requiring more energy to remove an electron.

       • Down a group, the addition of electron shells means outer electrons are farther from the nucleus and experience more shielding, making them easier to remove.

3. Electronegativity

   • Electronegativity measures an atom's ability to attract and bond with electrons.

   • Trend: Electronegativity generally increases across a period and decreases down a group.

     • Explanation:

       • Across a period, increased nuclear charge results in a stronger attraction to electrons.

       • Moving down a group, increased distance and shielding reduce the nucleus's ability to attract bonding electrons.

4. Electron Affinity

   • Electron affinity is the change in energy when an electron is added to a neutral atom in its gaseous state.

   • Trend: Electron affinity generally becomes more negative across a period and can vary down a group.

     • Explanation:

       • Atoms with higher electronegativities tend to have more negative electron affinities because they are more eager to gain electrons.

       • Down a group, the trend can become unpredictable due to the increased atomic size and electronic configurations.

5. Metallic Character

   • Metallic character refers to how readily an element can lose an electron.

   • Trend: Metallic character decreases across a period and increases down a group.

     • Explanation:

       • Elements on the left side of the periodic table (metals) are more likely to lose electrons than those on the right (nonmetals).

       • Moving down a group, the increase in atomic radius and electron shielding makes it easier for elements to lose electrons.

Trends Summary

The atomic radius, ionization energy, electronegativity, electron affinity, and metallic character all show specific trends within the organization of the periodic table, which are influenced by the arrangement of groups and periods.

Reference: Chemistry The Central Science (14th Edition)