(i)    State the shape of the electron distribution around the oxygen atom
       in the water molecule and state the shape of the molecule.
………………………………………………………………………………………….
………………………………………………………………………………………….

(ii)    State and explain the value of the HOH bond angle.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
…………………………………………………………………………………………..
Ans : (i)    tetrahedral (accept correct 3-D diagram);
                bent/V-shape/angular (accept suitable diagram); 
        (ii)    105° (accept 103 – 106°);
                lone pairs repel each other more than bonding pairs; 
                Do not accept repulsion of atoms.


(iii)   Explain why the bonds in silicon tetrachloride, SiCl4, are polar,
       but the molecule is not.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
Ans : bonds are polar as Cl more electronegative than Si;
         Allow “electronegativities are different”
         molecule is symmetrical, hence polar effects cancel out/OWTTE;


(iv)   Which of the following increase(s) for the bonding between carbon atoms
        in the sequence of molecules C2H6, C2H4 and C2H2?
        I.    Number of bonds
        II.    Length of bonds
        III.    Strength of bonding
        A.    I only
        B.    I and III only
        C.    III only
        D.    I, II and III
Ans: B