How Do Electronegativity Differences Influence Bond Type?

[bjoyful]

Homework Statement

NaCl is an ionic compound, but chlorine and silicon are joined by covalent bonds in SiCl4

A. Use Table 5.4 (page 229 of your text) to determine the electronegativity difference between chlorine and sodium, and between chlorine and silicon. What values did you calculate in each case?
B. What general correlations can be drawn about the electronegativity difference between bonded atoms and their tendency to form ionic or covalent bonds?
C. How can you explain on the molecular level the conclusion you reached in part B?

The Attempt at a Solution

A. Cl (3.0) – Na (0.9) = 2.1. Cl (3.0) – Si(1.8) = 1.2

Other than question a, I am not sure what I am doing.

 

[LtStorm]

For B, you need to look at SiCl4; it's a tetrahedral molecule, and has those four chlorine atoms all pulling in equal but opposite directions, causing their pull to cancel out. That's why it's left covalent. Whereas NaCl is an incredibly lop-sided molecule where the sodium has all but had its electron ripped out of it and gobbled up by the chlorine atom.

So that's what makes the difference between ionic and covalent molecules; ionic happens when there's a great electronegativity difference in the two. Covalent can either mean there's a small difference in electronegativity, or the molecule is arranged in such a way that it's dipole is canceled by opposite by equal pulls by its atoms.

 

[Blueshift5]

B. Generally, a larger electronegativity difference between bonded atoms leads to the formation of ionic bonds, while a smaller electronegativity difference leads to the formation of covalent bonds.

C. Electronegativity is a measure of an atom's ability to attract shared electrons in a chemical bond. When there is a large difference in electronegativity between two atoms, one atom will have a much stronger pull on the shared electrons, resulting in the formation of an ionic bond. This is because the more electronegative atom will gain the electron(s) from the less electronegative atom, forming ions with opposite charges that are attracted to each other. On the other hand, when there is a smaller difference in electronegativity, the shared electrons are more evenly distributed between the atoms, resulting in a covalent bond. In the case of SiCl4, the electronegativity difference between chlorine and silicon is smaller, making it more favorable for them to share electrons in a covalent bond rather than transfer them in an ionic bond.