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is BeCl2 covalent or ionic ?

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  • Bigcable22's Avatar
    293 posts since Mar '08
    • is BeCl2 covalent or ionic ?   if it is ionic compound with covalent characteristics do i treat it as covalent or ionic for doing mcq?

  • 16/f/lonely's Avatar
    5,858 posts since Apr '08
  • Moderator
    A Levels H1 & H2 Chemistry Tuition @ BedokFunland JC
    UltimaOnline's Avatar
    4,598 posts since May '05
    • Originally posted by Bigcable22:

      is BeCl2 covalent or ionic ?   if it is ionic compound with covalent characteristics do i treat it as covalent or ionic for doing mcq?

       

      It is covalent, due to the high electronegativity and high charge density (both these properties, relative to the rest of Group II metals). Its high electronegativity prevents complete loss of electrons to form cations which are stable on their own (required for formation of ionic compounds). Its high charge density attracts and causes lone pairs from chlorine to form bond pairs with itself.

       

      As a gas, it is simple covalent. As a solid, it is a polymer macromolecule (with dative covalent bonds between the chlorine and beryllium atoms of adjacent molecules).

       

      One interesting point to note, about beryllium complex ions, is that being in period 2, it does not have empty 3d orbitals with which to expand its octet. Consequently, beryllium complex ions are 4-coordinated, meaning they can at most have 4 bond pairs, eg. [Be(H2O)4]2+.

       

      This is in contrast with magnesium (also in Group II), which are 6-coordinated, eg. [Mg(H2O)6]2+.

      Edited by UltimaOnline 08 Jan `09, 11:19PM
  • Bigcable22's Avatar
    293 posts since Mar '08
    • Originally posted by UltimaOnline:


      It is covalent, due to the high electronegativity and high charge density (both these properties, relative to the rest of Group II metals). Its high electronegativity prevents loss of electrons to form cations (required for ionic compounds). Its high charge density attracts and causes lone pairs from chlorine to form bond pairs with itself.

       

      As a gas, it is simple covalent. As a solid, it is a polymer macromolecule (with dative covalent bonds between the chlorine and beryllium atoms of adjacent molecules).

       

      One interesting point to note, about beryllium complex ions, is that being in period 2, it does not have empty 3d orbitals with which to expand its octet. Consequently, beryllium complex ions are 4-coordinated, meaning they can at most have 4 bond pairs, eg. [Be(H2O)4]2+.

       

      This is in contrast with magnesium (also in Group II), which are 6-coordinated, eg. [Mg(H2O)6]2+.

       

      Woot perfect answericon_biggrin.gif

    • so its actually a giant covalent compound in solid state..

    • wanna use this thread to ask another question..

       

      what is the shape of CH3CH=CH2?

      and double check is the shape of HNO3 trigonal planar? as the H ion is dative bonded to 1 of the O atom hence i should consider only the 3bond pairs of electrons around N atom ?

  • Moderator
    A Levels H1 & H2 Chemistry Tuition @ BedokFunland JC
    UltimaOnline's Avatar
    4,598 posts since May '05
    • Originally posted by Bigcable22:

      wanna use this thread to ask another question..

       

      what is the shape of CH3CH=CH2?

      and double check is the shape of HNO3 trigonal planar? as the H ion is dative bonded to 1 of the O atom hence i should consider only the 3bond pairs of electrons around N atom ?

       

      >>> what is the shape of CH3CH=CH2? <<<


      You have to specify, "about which atom?". Look at how many lone pairs and bond pairs each atom has, to determine the geometries within the molecule.

       

      Also, you should be able to distinguish between electron geometry (which tells you the hybridization of the atom) versus molecular geometry (which tells you the shape of the molecule).

       

      For instance, what is the hybridization of N in the ammonia molecule? Since it has 4 electron pairs, the electron geometry is tetrahedral and the N is sp3 hybridized. But since one of the 4 electron pairs is a lone pair, the molecular geometry is trigonal pyramidal.

       

       

      For CH3CH=CH2

      Eg. the 1st C (sp3 hybridized) is tetrahedral, the 2nd C (sp2 hybridized) is trigonal planar, the 3rd C (sp3 hybridized) is trigonal planar.

       

       

      >>> and double check is the shape of HNO3 trigonal planar? <<<

       

      HNO3 or nitric(V) acid :

       

            -

           O

             \

           + N = O

             /

      H--O

       

      (+ve formal charge on N atom, since it is in Group V but only has 4 bond pairs (maximum octet as it has no empty d-orbitals to expand its octet); -ve formal charge on 1 O atom, since it is in Group VI but it has 3 lone pairs and 1 bond pair)

       

       

       

      Conjugate base - NO3- or nitrate(V) ion :

       

        -

       O

         \

       + N = O

         /

       O

        -

       

      (+ve formal charge on N atom, since it is in Group V but only has 4 bond pairs (maximum octet as it has no empty d-orbitals to expand its octet); -ve formal charge on 2 O atoms, since they are in Group VI but they have 3 lone pairs and 1 bond pair)

       

       

      The fact is, to draw Kekule structures of a molecule or polyatomic ion correctly, you need to be familiar with the concept of formal charges, which is often neglected by many JC teachers.

       

      Similarly, to have a proper understanding of Organic Chemistry, you need to be familiar with the concept of resonance, which again is often neglected by many JC teachers.

       

      But if you come for my tuition, I will definitely teach it to you (all my students), as these concepts (among many others) are fundamental and integral to a proper understanding and appreciation of Chemistry.  

      Edited by UltimaOnline 09 Jan `09, 1:17PM
  • Bigcable22's Avatar
    293 posts since Mar '08
    • thx for your answers

      yep i also feel odd about bond angle about which atom the question just ask whether is ch3ch=ch2 planar,,    actually my school havent reach organic chemistry yet,, this question is set on focus of chemical bonding shapes.. but dunno why they ask something that is not taught yet dang..

       

       

  • Moderator
    A Levels H1 & H2 Chemistry Tuition @ BedokFunland JC
    UltimaOnline's Avatar
    4,598 posts since May '05
    • Originally posted by Bigcable22:

      thx for your answers

      yep i also feel odd about bond angle about which atom the question just ask whether is ch3ch=ch2 planar,,    actually my school havent reach organic chemistry yet,, this question is set on focus of chemical bonding shapes.. but dunno why they ask something that is not taught yet dang..

       

      >>> yep i also feel odd about bond angle about which atom the question just ask whether is ch3ch=ch2 planar. <<<

       

      That by itself, is a valid question. And it's not the same as "what shape is the molecule?". You see, when asked whether it is planar (ie. flat, 2-dimensional, like a piece of paper), you simply have to say, "No." and explain "because there are 2 sp3 hybridized carbon atoms in the molecule with a tetrahedral geometry."

       

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