TOPIC 1: ELEMENTAL AND ENVIRONMENTAL CHEMISTRY SUBTOPIC: PERIODIC TABLE Electron configuration 1) Defin ed as t he arr angement of e lectr ons ar ound nucle us 2) Give s info on th e chemical behav iour o f the atom Brief History on Model of Atom 1) The ea rlies t mod el of at om was put fo rward b y Tho mson i n 189 8. a. Atom consi sts of posi tivel y cha rged sp here e mbedd ed wit h electrons. b. Mod el of at om wa s kno wn as ‘P lum Pu ddi ng At om’ 2) Erns t Ruther ford test ed Thoms on’s th eory in the famo us exper iment wh ere gold ato ms in the thin gold foil were bombarded with He nuc(alpha particle). a. His exp erimen tal resu lts sho wed tha t some alph a partic les wen t straig ht thro ugh the thin gold foil, some were slightly deflected and some came right back from where they come from. b. His ex perime ntal f indin gs did n ot sup port Thomso n’s mod el of ato m c. Ruthe rford p ropos ed tha t es orbi t the cen tral de nse nu c like in s olar s ystem i e. Microsolar system d. Howe ver, th ere are 2 prob lems as soci ated with th is new theor y i. Accor ding to law of cl assi cal phy sics , e orbit ing nu c would lose it s energy in the form of electromagnetic radiation, the movement of e would slow down and eventually collapse and spiral into nuc. (Unstable model) ii. This model could not ex plain why ato ms of diff erent element a bsor b oremit certain light of unique frequencies. (LES and Absorption Spectrum.) 3) In 190 0, Max Pl anck (German ph ysici st) de velop ed Qua ntum Theory . a. Accor ding to th is the ory li ght i s a stre am of t iny p acket s of ene rgy. b. The energy is abso rbed o r emitt ed in q uant a or pac kets of energy. c. E=hv where h=6.63×10 -34 Js d. This th eory wa s confi rmed by Ein stein i n 1905 usi ng expe rimen t on photo elect ric effect 4) In 1913 , Niels Bohr (Dan ish Phys icist ) propos ed ‘Bohr Mode l’ or ‘Bohr Theor y’, whic h was developed based on Quantum Theory. 1