ECU 100: Chemistry for Engineers I, Modern Periodic Table and Electronic Configuration

The periodic table and electronic configuration lecture of the first-year engineering chemistry unit. It opens with Mendeleev's periodic law, the arrangement of elements in increasing order of atomic weight into groups and periods, and the defects of that table: the anomalous position of hydrogen, which resembles both alkali metals and halogens, and the separation of similar elements while dissimilar ones are grouped together. Mosley's demonstration that properties are a periodic function of atomic number follows, then the extended long form with its eighteen columns: valence electrons, the representative elements of groups one to seven A, the alkali and alkaline earth metals, the transition elements of the B groups with the iron, palladium and platinum triads, the lanthanides and actinides below the main body of the chart, the metalloids along the diagonal between metals and non-metals, the halogens and the unreactive noble gases. The general characteristics of a group and of a period are then taken in turn - valency electrons, valency with respect to oxygen, properties, atomic size, metallic character, number of shells and the diagonal relationship of lithium with magnesium, beryllium with aluminium and boron with silicon. The second half is atomic structure: the distribution of electrons in shells, sub-shells and orbitals and the notation that names them, the Bohr-Bury limits on the electrons a shell can hold, the quantum numbers and the sub-shells they fix, Hund's rule of maximum multiplicity and the extra stability of half-filled and completely filled sub-shells, worked configurations from hydrogen through to krypton with the chromium and copper exceptions spelled out, and a closing summary of how to write the configuration of any s- or p-block element from its group and period.