Lecture #11, February 7, 1997
Isoelectronic systems defined.
The [Ne] isoelectronic species
Size depends on Zeff
Electron dot structures for the lightest elements contain dots to represent valence electrons.
What is electronegativity? Use sodium chloride as an example.
The lattice energy involves bringing together molecules of NaCl to form a macroscopic solid.
Electronegativity involves both ionization energy (difficulty in removing an electron) and electron affinity (ease of adding an electron) to an atom
Display of electronegativites for the first several dozen elements
Looking at just the main group elements, note that electronegativity has periodic behavior and increases in going from left to right across a given row of the Periodic Table
Similarly, the electronegativity decreases in going down a particular Group or column of the Periodic Table
The most electronegative elements (greatest tendency to form X-
The least electronegative elements (also called the most electropositive elements with the least tendency to add an electron -- or the greatest tendency to give one up during bond formation.
An ionic bond is formed between two atoms whose electronegativities are substantially different...> 2.
An example of ionic bond formation
Energy considerations indicate what is unlikely to happen as well as what is likely to happen.
When electronegativity differences are near zero, we talk about "covalent" bond formation.
Intermediate between the ionic bond and the covalent bond are the partially ionic (or polar covalent) bonds.