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Please help me with this chemistry question:plz help i really dont get this...

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foram | Student, Grade 11 | eNotes Newbie

Posted May 14, 2010 at 2:00 PM via web

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Please help me with this chemistry question:

plz help i really dont get this question.....x(

here it is...

the bonding in covalent latticesis described as DIRECTIONAL whereas that in ionic and metallic lattices is said to be NON-DIRECTIONAL. what do you think is meant by these terms?

plz plz i have NO IDEA about this... :(

plz help

thanks you soooooooo much

1 Answer | Add Yours

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hnystrom | High School Teacher | (Level 1) Assistant Educator

Posted July 12, 2010 at 7:58 PM (Answer #1)

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In an ionic lattice structure you have positively and negatively ions attracted to each other holding the whole lattice together.  In any one direction the positive and negative ions alternate.  So a negative ion, for example, would have a positive ion above it, one below it, one on either side, one front and and one back.  Each ion is equivalent, there is no difference, so there is no unique direction to the forces that hold that negative ion there.  It is non-directional.

In a metal lattice the metal ions are arranged in a lattice with a shared orbital for the valence electrons to travel in.  Again, for any one metal ion the ions all around it are the same so we call it non-directional.

In a covalent lattice there are individual shared molecular orbitals that form the bonds between atoms.  Molecular orbitals have some symmetry but not the complete all around symmetry that the metal and ionic lattices do.  In graphite, for example, the horizontal bonds between carbon atoms are strong but the vertical bonds are weaker.  The graphite tends to break along the vertical bonds forming sheets.  There is a sense of direction in this structure: horizontal=strong bonds, vertical=weak bonds.  This is why it is called directional.

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