♥ Dreams can die, hope shouldn't

Friday, October 07, 2005 { 3:07 PM }

haha. stayed in school to study today. so wu liao lor.. towards the end. left with lily shun and dq. den we were all listening to the smae radio station. and so i suggested some stupid game. we were supposes to guess the name of the song.. haha. and we were supposed to 'qiang da'. the first person who hits lily's plush crab gets to answer. wahaha. so dumb. and we were listening attentively to 933 cos we want to join the song guessing game. haha.. soooo much money to be won lor. haha. for the ske of my nano. hmmm. lolx. oh and den arh... kat called me.. den cos my screen was quite dark so i couldnt really see the number.. den when i picked up i heard her saying kat so i thought she was looking for kat. hahaha. and i told her wrong number..! lolx. den when i realised it's her i called her back... wahahaha. lolx. haha. kat kat.. it was a pleasant surprise. lolx. and i know you are DAMN free. hmpff.

hm. im back to my old studying methods. oh yes.. the one that helped me fail so many tests and exams. -.- wahaha. haix. dunno lar. no time no time. and what am i doing online right. haha. not that i want come online lor.. but the teachers are posting answers online so that gives me an excuse. haha. not that im complaining about them using the ivle lar.. but just.. it makes me come online... and waste my time away.

okok.. i shall make good use of my time. there's inorg test tmr eh. so sian lor. i wanna do well for it.. boost my confidence a bit hor. hur hur. okies. you pple can just read till here... cos the next part will just be a regurgitation of facts. wahaha. im just lazy to write them down.

ok, here it goes:
variation of ionic radii across period 3
Fron Na+ to Si4+, there is a decrease in cation radius. there is an increase in nuclear charge due to the increase in proton number. the cations are isoelectronic, i.e they have the same number of electrons. screening effect remains approx constant as they have the same no. of quantum shells of e. thus the same no of electrons is now more strongly attracted to the increasing nuclear charge. thus cation radius decreases from Na+ to Si4+.
there is a sharp increase in the ionic rad from si4+ to P3- as anions have one more shell of electrons than the cations.
repeat the same for anions.

melting point across period 3
(im feeling sleepyyy)
from na to al, the elements have giant metallic structures. melting involves overcoming the strong elctrostatic forces of att between the metal cations and the sea of delocalised e. the m.p increases due to the stronger metallic bond strength since there is an increaes in the no of e contributing to the sea of delocalised e.
si has a very high melting pt. it has a giant molecular structure with extensive covalent bonds betwwen the si atoms in the 3d arrangement. large amts of E is reqd to overcome the numerous strong covalent bonds between the atoms in this extensive structure.
from p to ar, the elements have low m.p. they are simple molecular structures with weak vdw forces of att between the molecules. less at of E is reqd to overcome these weak vdw forces of att. thus they have low m.p.

period 3 chlorides
when nacl dissolves in water, only hydration takes place with no hydrolysis. this is due to the low charge density of na+. hence nacl is neutral with pH 7.
nacl(s) + aq --> na+(aq) + cl- (aq)
mgcl2 undergoes hydration with slight hydrolysis in water due to the higher charge density of mg2+. mgcl2 forms a slightly acidic soln in water oh pH 6.5
mgcl2(s) + H20(l) --> [mg(H20)6]2+(aq) + 2cl-(aq)
[mg(h20)6]2+(aq) <--> [mg(h2o)5(oh)]+(aq) + H+ (aq)
al2cl6 undergoes both hydartion and hydrolysis in water due to the relatively high chrg density of al3+. this polarises the surrounding water molecules, thus weakening the o-H bond, causing h+ ions to be relesed more readily, giving rise to a soln of pH 3.
similar as mgcl2.
sicl4 and pcl5 undergoes complete hydrolysis to give a strongly acidic soln of pH 2.

thermal stability of group 2
down the group, cation size increases while charge remains unchanged. thus there is a decrease in charge density and so polarising power og the metal cation decreases. the cation is thus less able to distort the electron cloud of the anion and so the compound is more stable. larger amt of E is thus reqd to decompose the cpd.

volatility of group 7
down the grp, m.p increases. they have simple molecular structures and the exist as non polar diatomic molecules. melting involves overcoming the weak intermolecular id id forces of att. down the grp, molecular size of the cation increases. there is a greater extent of the distortion of the electron cloud. hence stronger id id . more e reqd to overcome the vdw forces of att. thus higher m.p

cl2 + h2o <--> hcl + hclo.

thermal stability of hydrogen halides
thermal stabilty decrease. from hcl to hi, there s an decrease in b.e due the increase in atomic rad. bond length incraeses while bond strength decreases. less amt of E reqd to overcome the h-x bond.

acidity
from hcl to hi, bond dissociation energy decreases down the grp due to the increase in atomic rad. weaker h-x bond breaks more easily and h+ is release more readily. thus hi is a stronger acid.

reducing power
reducing power increaese dow the grp. bond lenghth increases.bond strenth decreaes. easier cleavge of hx bond. from cl- to i-, increase in molecular size. loss of val e more esily to act as r.a.

haha. yawns. oh well finish three topics le. still got the last topic. but it's a lotttt.... transition elements. ha. shant write down here. shall go and study le. hehe. shun wei... be prepared to buy me drink man. yeah yeah.