(a) Why ClF3 exists but FCl3 does not ?
(b) Why ICl3 is more reactive than I2 ?
(c) Using VBT theory describe shape of XeO4.

**OR**

(a) Why does Fluorine shows anomalous behavior ?
(b) Why sulphuric acid is oily and viscous liquid ?
(c) What happens when Cu reacts with cold dil

Question

(a) Why ClF3 exists but FCl3 does not ?
(b) Why ICl3 is more reactive than I2 ?
(c) Using VBT theory describe shape of XeO4.

**OR**

(a) Why does Fluorine shows anomalous behavior ?
(b) Why sulphuric acid is oily and viscous liquid ?
(c) What happens when Cu reacts with cold dilute HNO3 ?

Accepted Answer

>

> [!TLDR]
> (a) Only the larger, d-orbital-bearing halogen can be the central atom in an interhalogen — so ClF₃ exists but FCl₃ doesn't. (b) Interhalogens are generally more reactive than the parent halogens because their bonds are weaker/more polar. (c) XeO₄ is sp³ hybridised (4 bond pairs, 0 lone pairs) → tetrahedral.
>
> **(a) $ClF_3$ exists, $FCl_3$ does not:**
>
> In an interhalogen compound $XY_n$ ($n>1$), the central atom $X$ must be (i) larger than the peripheral atom $Y$ (to sterically accommodate multiple $Y$ atoms around it) and (ii) able to expand its valence shell (using low-lying vacant d orbitals) beyond the normal octet to bond to more than one $Y$ atom while retaining any lone pairs.
>
> In $ClF_3$, chlorine (period 3, larger, with accessible vacant 3d orbitals) is the central atom, and it comfortably expands its octet via $sp^3d$ hybridisation to bond to 3 (smaller) fluorine atoms plus 2 lone pairs.
>
> $FCl_3$ would require fluorine (period 2) to be the central atom — but fluorine has no d orbitals available at all (only $2s, 2p$), so it cannot expand its octet beyond 4 electron pairs total, and being also the *smallest* halogen, it cannot sterically host 3 larger chlorine atoms around itself. For both electronic and steric reasons, $FCl_3$ does not exist.
>
> **(b) $ICl_3$ more reactive than $I_2$:**
>
> Interhalogen compounds are, as a rule, more reactive than the parent halogens (other than $F_2$ itself) because the bond between two *different* halogens (e.g. I–Cl) is inherently weaker and more polar than the bond between two *identical* halogen atoms (I–I), owing to the difference in electronegativity/size giving less effective orbital overlap in the heteronuclear bond. This weaker, more polar X–Y bond breaks more easily during a reaction, so $ICl_3$ reacts (e.g. as a halogenating agent) more readily than $I_2$.
>
> **(c) Shape of $XeO_4$ (VBT):**
> …

Q.(a) Why ClF3 exists but FCl3 does not ?

Concept understanding — p-Block Elements

Q.(a) Why ClF3 exists but FCl3 does not ?

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