Answers to Worksheet 5 � Chemical Bonding

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					Answers to Worksheet 5 – Chemical Bonding
Science(Chemistry) Theory Workbook Pg 36 to 45

Check It ( 37 to 39 )

1. C        2. B    3. D      4. A      5. B       6. A     7. D     8. B    9. B

10a)     calcium oxide and potassium chloride
  b)     carbon dioxide and methane
  c)     calcium oxide or potassium chloride ( any one, an ionic one )
  d)     carbon dioxide or methane ( any one, a covalent one )
  e)     helium ( a noble gas , is monatomic, as single atoms)

11a) C :( 2,4 ); O :( 2,6 ); Na :( 2,8,1 ); Si :( 2,8,4 ); Cl :( 2,8,7 )
b)(i) No. of neutrons = Nucleon no  no of protons = 9 – 4 = 5
 (ii) No. of neutrons = 28 – 14 = 14
c) Beryllium and sodium (are metals, but, diamond does not conduct)
d)(i) NaCl, sodium chloride
  (ii) Na2O, sodium oxide
  (iii) CO2, carbon dioxide or CO, carbon monoxide
  (iv) Na2CO3, sodium carbonate (C and O forms the radical ion CO32- )
e) Carbon dioxide is a covalent compound with a simple
       molecular structure. It is made up of small molecules with
       weak intermolecular forces of attraction between
       molecules. Little amount of heat energy is needed to
       overcome these weak forces. Thus, it has a low boiling
       point and is a gas at r.t.p.

Notes: I.      Type of Bonding -     Ionic     &    Covalent

  II.                         Structure


            Ionic compounds          Covalent substances


       Giant Ionic            Giant molecular             Simple molecular
       lattice structure      (macromolecular)            structure
                              structure




                                                                                    1
 Practice Question ( Pg 41)
 a)
  Element           Proton               Nucleon     Number of       Electronic configuration
                    number               Number       neutrons
         W             7                   14         14-7 = 7                   2,5
         X             9                   19         19-9=10                    2,7
         Y            10                   20            10                      2.8
         Z            11                   23            12                     2,8,1

b(i)         Z. Metals usually have less than 4 valence electrons. Since Z
             has only one valence electron, it is a metal and it tends to lose
             its one outer shell electron to form a positive ion to achieve the
             stable noble gas electronic configuration.

(ii)     W, X and Y. Non-metals usually have more than 4 valence
          electrons. As these elements have 5 or more valence electrons,
          they are non-metals and tend to gain electrons to form
          negative ions to achieve the stable noble gas electronic
          configuration.

 (iii) Y. It has a completely filled valence shell of 8 electrons.

 C(i) X and X form X2

              XX                    
                                                   (X is non-metallic atoms, so two of it
                        X                         will form a covalent bond to become
       X X X                        X
                                       
                    X
                                                   a diatomic molecule)
       X                                     
               XX                   

   ii)        X and Z form ZX
                                          XX          

                                                            metal Z and non-metal X
         Z                                X       X
                                    X X           X X        forms ionic bond, metal atom
                                                             is named and drawn first

                                           XX




                                                                                             2
 iii) W and X form WX3

                                                                     Both non-metallic W and
                                                xx
              xx                                                     X atoms form covalent
                                                                     bond.
    x                 x W               x x     X x       x        Each W atom ( 2,5) needs
    x x       X     x                                     x
                                                                     3 electrons while each X
                                   x                                atom ( 2,7) needs 1
                                                  xx
              xx                                                     electron to complete the
                       x                  x
                       x x         X    x x                          outer shell. So one W
                                                                     atom bonds with 3 X
                                                                     atoms by sharing
                                   xx                                electrons.


Test It ( Pg 42 to 45 )
                       56                                                           56
   1.     D        (        Fe loses 3 e’s becomes 56Fe3+ or 2 e’s to become             Fe2+ , no
                           change in no. of protons and neutrons)
   2.     D        ( Both are negative ions since they have more electrons than
                    protons and are from non-metals )
  3.      A        ( X : 3p, 3e (2,1) X is a metal forms X+ ion while Y : 8p, 8e ( 2,6)
                         Y is a non-metal,forms Y2- )
   4.     C         (low bp, so covalent, if Cl is non-metal, then Q must be non-metal)

   5.     B        ( particles can be ions, atoms or isotopes
                             R:p=e            S:p>e              T:p<e       V:p=e
                               atom           +ve ion             ve ion      atom         )

   6.     B        ( strong ionic bond ( electrostatic force of attraction between
                     ions in ionic compounds requires large amount of energy to
                    overcome)
  7.      A       ( correct one is Na3P since P( 2,8,5) gives P3- and bond with Na+ )


   8.     B       ( S (2,8,6) require 2 electrons and Cl (2,8,7) require 1 electron
                  a single line ‘ ’ 2 electrons( 1 pair); double ‘=’ 4 electrons (2 pairs))
                                      xx        xx        
                                   x         x         x            
                             Cl         S        S            Cl
                                             x                      
                                      xx        xx            



                                                                                                     3
9.    B     ( sodium fluoride , ionic compound ,made up of Na+ and F- ions in a
             giant ionic lattice structure )
10.    B   ( There is covalent bond between N and H atoms in the ammonium ion
             ( NH4+) and ionic bond between the NH4+ ion and Cl- ion)
11a)
                   xx
                                         -- electron of H
                   O                     x – electron of O
           x                x
                       
       H           xx
                                H

b) ( one single bond (line) has 2 electrons)
Thus, total number of electrons shared = 5 x 2 = 10 electrons
12a)    5               b)     4
c)(i)   10
(ii)    ( 6 x 1 ) + ( 4 x 1) = 10
(iii)   (6x1)+(4x0)=6
d)      Si ( 2,8,4) ; C ( 2,6)
       Thus, there is increase of 8 electrons, so the new
        molecule has 18 electrons.
13a) CCl4 and PCl5
b)(i) BeCl2         (ii) SiCl4
c) Neon and argon are both noble gases which have stable
       electronic structures with completely filled outer shells and
       so do not form bonds with other elements.
d) BCl3, OCl2, ClF, S2Cl2 and Cl2. Their boiling points are
     below 300C.
  e)(i) Lithium loses an electron to chlorine and forms lithium
        ion. Chlorine gains an electron to form chloride ion.
        The positive lithium ion is attracted to the negative
        chloride ion forming an ionic bond.
  (ii)     ClF is formed by covalent bonding between the two
        non-metals whereby a pair of electrons is shared
        between the chlorine and fluorine atoms.




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