Ch9-PERIODICITY AND IONIC BONDING

Electrostatic principles

1. Opposite charges attract

2. Like charges repel

3. As charges increase, so does attraction/ repulsion

4. As two charged bodies get closer together, the force of attraction/repulsion gets stronger

Effective nuclear charge, (Z_eff)

• Net positive charge felt by valence electron from the nucleus

  • Lower than actual charge

• The difference is shielded by inner electrons

• Z_eff increases across periods and decreases down groups

Atomic radius

• Decreases across period due to increase in Z_eff

• Addition of protons increases positive nucleus charge and its pull on electrons

• Meanwhile, increase in valence electrons shields the others

• Increases down groups due to increasing principal quantum number

Ionic radius

• Increases down groups, decreases across period

• Cations are smaller than neutral atoms

• Anions are larger than neutral atoms

Ionization energy, second, third

• Energy required to remove an electron

• Increases across period and decreases down groups

• Increases as atomic radius decreases because it is more difficult to remove an electron that is closer and more strongly attracted to nucleus

• Second ionization energy- energy required to remove an electron from the +1 ion

• Third ionization energy- energy required to remove electron from the +2 ion

Electron affinity

• Change in energy when electron is added to atom to form anion

• Negative electron affinity means release of energy (exothermic)

• Positive electron affinity means energy must be added (endothermic)

• Halogens have the most negative electron affinities

Lattice energy

• energy released when ions assemble into a lattice

• Lattice energy decreases as size of anions and cations increase

• Formation of ionic compounds become less exothermic as size of ions increase

• Ionic compounds that have larger ions have longer ionic bond lengths and electrostatic attraction between ions weakens as nuclei move apart