IIT JEE , AIEEE Forum - Chemistry , Inorganic Chemistry

sonal_01

hi,

as everybody till now wud hav done their chemistry preparations ,i wud request u to plz post some EXCEPTIONS in trends n sequences that we come across while studying chem,for eeg H3PO3 is more acidic than H3PO4

plz post exceptions with reasons,u can post both from organic and inorganic

experts plz post some such exceptions n important points in chem

it will help us all.

RATES ASSURED

ashgirl

the dipole moment of CH3F is lower than CH3Cl though the dipole moment shud decrease as we go down!!

paddy.dude

for example oxygen and chlorine r both similar in electronegativity.....but only oxygen forms hydrogen bonds......why

answer is becoz of larger size of chlorine it cant form hydrogen bonds

paddy.dude

fluorine being most electronegative has lesser electron affinity thatn chlorine becoz there exits repulsions among the non bonding electrons in flourine due to which incoming electron does not face much attraction

gain

ELECTRON AFFINITY:--
Among nonmetals, however, the elements in the first period have lower electron affinities than the elements below them in their respective groups.
Elements with electron configurations of Xs², Xp³, and Xp⁶ have electron affinities less than zero because they are unusually stable. In other words instead of energy being given off, these elements actually require an input of energy in order to gain electrons. e.g. Be, N, Ne
- WHY? - Electron affinities are all much smaller than ionization energies.
  1. Xs² < 0: Stable, diamagnetic atom with no unpaired electrons.
  2. Xp³ < 0: Stable atom with 3 unpaired p-orbital electrons each occupying its own subshell.
    Xp⁶ < 0: Stable atom with filled valence (outermost) shell.

avi_1214545

in aq. medium

the basicity of methyl sustituted amines have the order::
2⁰>1⁰>3⁰>0⁰while that of ethyl substituted amines have the order::
2⁰>3⁰>1⁰>0⁰

avi_1214545

the bp of HF is the highest among HF,HCl,HBr,HI
and the order is
HF>HI>HBr>HCl

the only rason being

VERY STRONG intermolecular H BONDING in HF that allows molecular association and increases bp to paramount value

paddy.dude

well avi ur slightly wrong.....the order u told for amines is true but only in aqueuos medium..........

avi_1214545

thanx for the correction...dude....dunno how cud i 4get it...

narulaajun

well avi can u explain y basicity follows that trend in aq. medium plz

sneha.bagri

Jones reagent

CrO3 -H2SO4

alcohol to carboxylic acid

sneha.bagri

though not a trend but dis is given only in solved ex. of ncert and not in d ch.

avi_1214545

sure

the reasons are........

STERIC HINDRANCE and SOLVATION ENERGY....which disallows tertiary amine to be most basic..........

Now in methyl substituted tertiary amine.....these effects are more (in magnitude) than the I effect of three methyl groups.....so its even less basic than primary.......

but in ethyl substituted tertiary amine......these effects are lesser (in magnitude) than the I effect of three ethyl groups.....so its more basic than primary...but less basic than primary..........

KEERU

the bond energy of halogens follows the order

Cl₂>Br₂ >F₂ >I₂

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