Periodicity

 
3.1 The Periodic Table

3.1.1 : Elements increase in atomic number across each period, and down each group. The history is boring and pointless (like all history)...ignore it.

3.1.2 : Group - the columns going down. Period - the rows going across.

3.1.3 : Group = number of valence electrons in the atom. Period = number of main electron shells...s, p , d and f blocks as described above.

3.2 Physical Properties

3.2.1 :

Li->Cs (down the alkali metals) : Atomic radius increases due to increased electron shielding. Ionic radius increases due to increased electron shielding. Ionisation energy decreases due to increased electron shielding. Melting/boiling point decreases due to increased electron shielding->decreased forces. Electronegativity decreases due to increased shielding -> decreased attraction for outer electrons.

F->I (Down the halogens) : Atomic radius increases due to increased electron shielding. Ionic radius increases due to increased electron shielding. Ionisation energy decreases due to increased electron shielding. Melting/boiling point increases due to increased number of electrons->increased london dispersion forces. Electronegativity decreases due to increased shielding -> decreased attraction for outer electrons.

Na->Ar (across period 3) : Atomic radius decreases due to increased nuclear charge -> greater attraction for electrons. Ionic radius decreases Na->Al (due to increased nuclear charge) jumps Al->Si (due to reversal of ionisation direction...increased electron-electron repulsion) decreases Si->Ar (due to increased nuclear charge). Ionisation energy increases due to increased nuclear charge. Melting/boiling point increases Na->Si (due to stronger metallic bonding - more delocalized electrons then network covalent) drops Si-P (due to network->molecular covalent) increases P->S (due to increased LDF between molecules ie P4, S8). Drops to Cl, due to smaller molecules (Cl2) decreases to Ar (individual atoms->fewer electrons->smaller LDF). Electronegativity increases due to increased nuclear charge -> greater attraction for electrons.

Interactive IB Chemistry Syllabus:
http://www.ibchem.com/IB/ibnotes/brief/per-sl.htm