structure and bonding?

Question

silicon tetrachloride SiCl4 has polar bonds but the molecule isn't polar right?? How come?

What kinds of intra and inter molecular bonds are there?

Answer 1

It helps to understand this question if you understand that bond polarity, when you are talking about the polarity of several individual bonds that are part of a larger molecule, is a VECTOR quantity - it has magnitude AND DIRECTION. Follow.

The geometry of a silicon tetrachloride (SiCl4) molecule is TETRAHEDRAL. The molecule consists of a central Si atom, which has a coordination number of 4. Four chloride (Cl) atoms can bond to Si. When they do, they assume a geometry AROUND the Si, in such a way as to put maximum distance between themselves/each other, and minimize repulsion. This results in a tetrahedral configuration. Therefore, the molecule has no net dipole moment...they all sort of "cancel each other out"

While each individual Si-Cl bond IS polar, that is, each Si-Cl bond has an individual dipole moment, the chlorides are spread evenly around the Si. The effect is that the Si-Cl dipoles are all pointing in different directions. So there can be no real separation of charge that would result in a net polarity, or a non-zero dipole moment.

Answer 2

SiCl4 is covalent compound. Si--Cl bond is polar because Cl is more electronegativity than Si. Structure of SiCl4 molecule is tetrahedral. THis structure is symmetry which brings to the non-polar characteristic of SiCl4 molecule. This is because all the dipole moment in Si--Cl bond cancel out each other.
The bond between Si--Cl is covalent bond. SiCl4 molecules hold together by intermolecular Van der Waals force of attraction. There is no intra and inter molecular hydrogen bond exist in SiCl4 molecule.

Answer 3

something to add to the above correct answers. Polarity of a molecule is created by an uneven distribution of electrons across the whole. If all the chlorine atoms were on the same side then there would be an abundance of electrons in that area, giving at a relative negative charge. As negative charges repel each other all of the chlorine atoms repel each other as far as possible around the silicon to give the tetrahedral arrangement, spreading the electrons evenly across the molecule; therefore no polarity.

Answer 4

Sicl4 Structure

Answer 5

SiCl4 has polar bonds yet it is non polar because of symmetry.it has a pyramidal structure.if u have seen the pyramids,u must have seen that all its four sides are in 4 opposite directions.same is case with SiCl4.all its bond moments are in opposite direction. that,s why vector addition of them yiels zero answer & overall molecule is non polar.
Chemical bonds are intramolecular force.so 4 covalent bonds in SiCl4 are intramolecular force. and since molecule is non polar so i think london dispersion force may be intermolecular force in SiCl4

Answer 6

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Hi Stephen: These questions are asked in the wrong order! 1) Use VSEPR to determine structure: Xe has 8 ve, 4 are used to bind the 4F atoms and 2e to bind O (needs 2e to complete octet). This leaves 2e on Xe so the system is AX5E with one lp occupying one site in the 6 coord sphere of Xe. Ignore lp when naming strucure so molecules is square lyramidal. There are two isomers but the one with Xe-O along the four fold axis is found (can rationalize this). Put vectors alonge (d+ve)Xe-F(d-ve) and Xe-O bonds. The Xe-F vectors cancel (no dipole) so we must consider polarity of the :-Xe=O bond. Probably Xe=O -> more -ve and hence molecule will be polar (I think in texts they just ignore the lp when considering polarity).. Hybrid use 4-coord = sp3, 5-coord.= sp3dz2, oct (6 coord) = sp3dx2-y2,dz2. Note N AOs give N hybrid AOs, d orbitas used are those that point at the ligand. So Xe is sp3d2 hybridized in Xe(O)F4. OK? dr p

Answer 7

Even if the molecule has only covalent bounds the chlorine atom is electronegative and attracts more the electrons than the silicium. So, there is a fictive negative charge on Cl in the bound Si-Cl.

Answer 8

It's because of the Egyptians.