Periodicity and Ionic Bonding Summary

Development of the Periodic Table

• 1864 - John Newlands proposed the Law of Octaves.

• 1869 - Dmitri Mendeleev & Lothar Meyer proposed periodicity.

  • Grouped elements by properties and predicted properties for undiscovered elements.

Modern Periodic Table

• Elements are classified into:

  • Main group elements (1A-7A).

  • Noble gases (8A), with $ns^2np^6$ configuration (except He).

  • Transition elements (1B, 3B-8B), the "d-block".

  • Lanthanides/actinides, the "f-block".

Valence and Core Electrons

• Valence electrons: Outermost electrons that display periodicity.

• Core electrons: All electrons that are not valence electrons.

• Valence electrons are involved in bonding and determine chemical properties. The number of valence electrons equals the "A" group number.

Effective Nuclear Charge ($Z_{eff}$)

• $Z$ (nuclear charge) = number of protons in the nucleus.

• $Z_{eff}$ = magnitude of positive charge experienced by an electron.

• $Z_{eff}$ increases from left to right across a period; changes little down a column.

• Shielding: Inner electrons shield valence electrons from the full nuclear charge.

Periodic Trends in Atomic Properties

• Atomic radius: Distance between the nucleus and valence shell.

  • Metallic radius: Half the distance between nuclei of adjacent metal atoms.

  • Covalent radius: Half the distance between adjacent nuclei in a molecule.

  • Atomic radius decreases across a period (increasing $Z_{eff}$).

  • Atomic radius increases down a column (increasing n).

Ionization Energy (IE)

• Minimum energy needed to remove an electron from an atom in the gas phase: $Na(g) \rightarrow Na^+(g) + e^-$.

• IE generally increases as $Z_{eff}$ increases across a period.

• IE generally decreases down a group as n increases.

• Multiple Ionizations: It takes more energy to remove subsequent electrons, especially core electrons, due to increased proximity to the nucleus and greater $Z_{eff}$.

Electron Affinity (EA)

• Energy change when an electron is added to a gaseous atom to form an anion: $Cl(g) + e^- \rightarrow Cl^-(g)$.

• Negative EA: Exothermic process (energy released).

• Positive EA: Endothermic process (energy required).

Periodic Trends

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

• Nonmetals: Poor conductors with high EA, forming anions.

• Metalloids: Properties between metals and nonmetals.

Electron Configuration of Ions

• Main group elements gain or lose electrons to become isoelectronic with noble gases.

• Ions of d-Block Elements: Electrons are lost from the highest n value first (4s before 3d).

Ionic Radius

• Cations are smaller than their parent atoms.

• Anions are larger than their parent atoms.

• Isoelectronic Series: Species with the same electron configuration but different nuclear charges; size varies significantly.

Chemical Properties of Main Group Elements

• Elements in the same group have similar properties due to the same valence electron configuration.

• Group 1A and 2A metals are active.

• Group 7A are halogens.

• Group 8A are noble gases.

• Metal oxides are basic; nonmetal oxides are acidic; amphoteric oxides are intermediate.