# why is XeF2 linear?

#### thebillsfan

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I have such a hard time remembering this, since SO2 is bent. I know CO2 is linear because it has double bonds, but I believe Xe-F bonds are single bonds in this molecule. And what about XeF4?

#### bruceleehiiiyaa

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I have such a hard time remembering this, since SO2 is bent. I know CO2 is linear because it has double bonds, but I believe Xe-F bonds are single bonds in this molecule. And what about XeF4?

okay think of it this way. XeF2E3 ---> trigonal bipyramidal orientation

where the E = 2 electrons, so 3 pairs of electrons.

but the F is attached to the TOP and BOTTOM of Xe, whereas the 3 pairs of electons are attached to the sides.

so, it looks linear.

#### Doodl3s

7+ Year Member
So i personally do understand electron geometry, as you explained, the electron pairs take up a slot. But how would you know its sp3d hybridized...? I know it can expand its octet.... but how do you know it goes to ten when it does that?

In other words I don't get how you figure out the electron geometry in things that expand their octets...

#### sleepy425

10+ Year Member
Ok, first we need to figure out the lewis structure of XeF2. To do that we first need to count up the total number of valence electrons we will need in the structure. Xe contributes 8 and each fluorine contributes 7 for a total of 22 valence electrons. So now draw Xe at the center with one bond to each fluorine. Since fluorine must obey the octet rule and doesn't tolerate a positive formal charge well, we fill in its electrons first. Since each already has two electrons from the bond we only need 6 more so we put 3 lone pairs on each fluorine. So we've used a total of 16 valence electrons now so we have 6 left. These have to go on the Xe as 3 lone pairs. Ok, now, to assign the geometry, we first look at the total number of bonds plus lone pairs on the central atom. That is five (2 bonds plus 3 lone pairs). Thus, the parent geometry that corresponds to 5 lone pairs plus bonds is trigonal bipyramidal (go look up what this looks like on wikipedia). Now, because you have 3 lone pairs, two positions of that parent geometry will be taken up by atoms, and the other 3 positions will be lone pairs. The lone pairs go in the positions that are farthest apart to minimize repulsion. Thus they go in the positions that are 120 degrees apart
(in the wikipedia picture these are the positions in the middle of the structure). This leaves the fluorine atoms at the top and bottom of the structure and since these are 180 degrees apart, it's linear.

Doodl3s, it is sp3d because you have 5 lp plus sigma bonds.

XeF4 has a total of 36 valence electrons. Each fluorine is single bonded plus 3 lone pairs so that is 32 electrons. So you put 2 lp on the Xe to give 36. Since bonds plus lp is 6, the parent structure is octahedral. Putting the two lone pairs as far apart as possible puts them 180 degrees apart leaving the 4 fluorines 90 degrees apart around the middle (again, a figure helps). That is known as square planar since they are all on the same plane 90 degrees apart.

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#### thebillsfan

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Ok, first we need to figure out the lewis structure of XeF2. To do that we first need to count up the total number of valence electrons we will need in the structure. Xe contributes 8 and each fluorine contributes 7 for a total of 22 valence electrons. So now draw Xe at the center with one bond to each fluorine. Since fluorine must obey the octet rule and doesn't tolerate a positive formal charge well, we fill in its electrons first. Since each already has two electrons from the bond we only need 6 more so we put 3 lone pairs on each fluorine. So we've used a total of 16 valence electrons now so we have 6 left. These have to go on the Xe as 3 lone pairs. Ok, now, to assign the geometry, we first look at the total number of bonds plus lone pairs on the central atom. That is five (2 bonds plus 3 lone pairs). Thus, the parent geometry that corresponds to 5 lone pairs plus bonds is trigonal bipyramidal (go look up what this looks like on wikipedia). Now, because you have 3 lone pairs, two positions of that parent geometry will be taken up by atoms, and the other 3 positions will be lone pairs. The lone pairs go in the positions that are farthest apart to minimize repulsion. Thus they go in the positions that are 120 degrees apart
(in the wikipedia picture these are the positions in the middle of the structure). This leaves the fluorine atoms at the top and bottom of the structure and since these are 180 degrees apart, it's linear.

Doodl3s, it is sp3d because you have 5 lp plus sigma bonds.

XeF4 has a total of 36 valence electrons. Each fluorine is single bonded plus 3 lone pairs so that is 32 electrons. So you put 2 lp on the Xe to give 36. Since bonds plus lp is 6, the parent structure is octahedral. Putting the two lone pairs as far apart as possible puts them 180 degrees apart leaving the 4 fluorines 90 degrees apart around the middle (again, a figure helps). That is known as square planar since they are all on the same plane 90 degrees apart.

thanks, sleepy. what do you mean by lp? do you just mean the azimuthal quantum number p?

also, consider BF3. I know Boron has 3 valence electrons as a lone atom. Does it mean anything to say, in BF3 boron has 6 valence electrons? I just did a question with an explanation that read: "boron has six valence electrons in compounds." That sounds weird to me--is it an accurate way of saying boron has six bonding electron in a compound? I would say that boron forms three single bonds for a total of six bonding electrons, but of those six, only THREE of them are BORON'S valence electrons. Am I right or are they right?

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#### sleepy425

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thanks, sleepy. what do you mean by lp? do you just mean the azimuthal quantum number p?

also, consider BF3. I know Boron has 3 valence electrons as a lone atom. Does it mean anything to say, in BF3 boron has 6 valence electrons? I just did a question with an explanation that read: "boron has six valence electrons in compounds." That sounds weird to me--is it an accurate way of saying boron has six bonding electron in a compound? I would say that boron forms three single bonds for a total of six bonding electrons, but of those six, only THREE of them are BORON'S valence electrons. Am I right or are they right?
sorry, I got lazy cuz I was typing it on my iPod. Anyway, lp is lone pair.

As far as the boron is concerned, i mean, it's just semantics. I mean, the truth is, valence electrons are just the atom's outermost electrons. Once you form compounds, the electrons are found in molecular orbitals and are technically not called valence electrons. So for BF3, boron contributes 3 valence electrons to the molecule, but in the molecule, boron has 6 bonding electrons since the fluorines share one electron each with the borons. Sorry I couldn't be more help with this

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#### thebillsfan

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no, you were a great help. in fact, your explanations are always fantastic. thanks