Molecular shape of Pbcl4
I was revising my old chemistry notes and saw the molecular shape of pbcl4 . I am confused. Isnt the proper molecule pbcl2 rather than pbcl4 . How can Lead have four electrons in its valence shell .
The shape has four bond pairs m and a bond angle of 109 degrees.
I am reading this after four months so please clear my confusion.
Thanks
The shape has four bond pairs m and a bond angle of 109 degrees.
I am reading this after four months so please clear my confusion.
Thanks
Lead has four valence electrons as it is in Group 4 in the periodic table, with carbon and silicon etc. Each one of these four electrons can form single covalent bonds with a chlorine atom, so you can make the molecule PbCl4. That doesn't mean you can't have PbCl2 as well, but that's slightly different.
Using a theory called Valence Shell Electron Pair Repulsion (VSEPR for short), you can predict the shapes of molecules such as PbCl4. Essentially, these covalent bonds (which each contain a pair of electrons) will arrange themselves to sit as far apart from each other as possible, as the electrons in the bonds repel each other.
The calculation is thus:
You know that Lead has 4 valence electrons as it is in Group 4.
Each Cl atom contributes 1 electron via a covalent bond, giving four more electrons.
4+4 is 8, so there are 8 electrons orbiting the lead nucleus. Divide this by two to give the number of electron pairs, which is four.
Now, these four pairs must sit as far apart as possible geometrically, so they form a tetrahedron in 3-D space. When you look at the angles between the bonds, they are all the same at 109.5 degrees.
Sorry if it's a little complicated.
This was posted from The Student Room's iPhone/iPad App
Using a theory called Valence Shell Electron Pair Repulsion (VSEPR for short), you can predict the shapes of molecules such as PbCl4. Essentially, these covalent bonds (which each contain a pair of electrons) will arrange themselves to sit as far apart from each other as possible, as the electrons in the bonds repel each other.
The calculation is thus:
You know that Lead has 4 valence electrons as it is in Group 4.
Each Cl atom contributes 1 electron via a covalent bond, giving four more electrons.
4+4 is 8, so there are 8 electrons orbiting the lead nucleus. Divide this by two to give the number of electron pairs, which is four.
Now, these four pairs must sit as far apart as possible geometrically, so they form a tetrahedron in 3-D space. When you look at the angles between the bonds, they are all the same at 109.5 degrees.
Sorry if it's a little complicated.
This was posted from The Student Room's iPhone/iPad App
Original post by Snakefingers13
Lead has four valence electrons as it is in Group 4 in the periodic table, with carbon and silicon etc. Each one of these four electrons can form single covalent bonds with a chlorine atom, so you can make the molecule PbCl4. That doesn't mean you can't have PbCl2 as well, but that's slightly different.
Using a theory called Valence Shell Electron Pair Repulsion (VSEPR for short), you can predict the shapes of molecules such as PbCl4. Essentially, these covalent bonds (which each contain a pair of electrons) will arrange themselves to sit as far apart from each other as possible, as the electrons in the bonds repel each other.
The calculation is thus:
You know that Lead has 4 valence electrons as it is in Group 4.
Each Cl atom contributes 1 electron via a covalent bond, giving four more electrons.
4+4 is 8, so there are 8 electrons orbiting the lead nucleus. Divide this by two to give the number of electron pairs, which is four.
Now, these four pairs must sit as far apart as possible geometrically, so they form a tetrahedron in 3-D space. When you look at the angles between the bonds, they are all the same at 109.5 degrees.
Sorry if it's a little complicated.
This was posted from The Student Room's iPhone/iPad App
Using a theory called Valence Shell Electron Pair Repulsion (VSEPR for short), you can predict the shapes of molecules such as PbCl4. Essentially, these covalent bonds (which each contain a pair of electrons) will arrange themselves to sit as far apart from each other as possible, as the electrons in the bonds repel each other.
The calculation is thus:
You know that Lead has 4 valence electrons as it is in Group 4.
Each Cl atom contributes 1 electron via a covalent bond, giving four more electrons.
4+4 is 8, so there are 8 electrons orbiting the lead nucleus. Divide this by two to give the number of electron pairs, which is four.
Now, these four pairs must sit as far apart as possible geometrically, so they form a tetrahedron in 3-D space. When you look at the angles between the bonds, they are all the same at 109.5 degrees.
Sorry if it's a little complicated.
This was posted from The Student Room's iPhone/iPad App
Then why does lead , make pb2+ , when it has four electrons in its valence shell?
Original post by mmaslam
Then why does lead , make pb2+ , when it has four electrons in its valence shell?
It's to do with sub-shells. I don't know how far you've got, but Pb is a bit further down the table, so it gets a lot more complicated - the '2 electron = 2+' rule only works up until Calcium / Potassium. I don't think you need to know for A-Level though (I don't know the details myself), but someone else on here may be able to help you more.
(edited 11 years ago)
Original post by mmaslam
Then why does lead , make pb2+ , when it has four electrons in its valence shell?
This is due to something called the 'inert pair effect'.
As lead is relatively massive it has many protons in the nucleus (82). This makes the 's' electrons tightly held and difficult to ionise (an inert pair).
It means that as you descend group IV (same argument for group III) the lower oxidation state becomes relatively more stable than the group oxidation state of IV.
Hence, carbon is stable in the IV oxidation state, but highly reducing in the II oxidation state, while lead is stable in the II oxidation state and highly oxidising in the IV oxidation state. The other elements fit in with this trend.
<hr />(edited 11 years ago)
Original post by mmaslam
Then why does lead , make pb2+ , when it has four electrons in its valence shell?
It is because after release ng 2 electrons it is stable because the 6s subshell is complete. Again , by period properties , the stability of +4 oxidation state decreses down the group. Hence Pb +2 is more stable than Pb +4
You shouldn't need to know why PbCl2 and PbCl4 form etc.
Unless you're doing the devil exam board WJEC, but I take you're not
Unless you're doing the devil exam board WJEC, but I take you're not
Original post by Putudegr8
It is because after release ng 2 electrons it is stable because the 6s subshell is complete. Again , by period properties , the stability of +4 oxidation state decreses down the group. Hence Pb +2 is more stable than Pb +4
Where the heck did you find a six year old thread? And why did you think the people who have now, no doubt, finished university would be interested in your answer?
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