Shapes of Molecules & Dot and Cross Diagrams HELP Watch

alevels2020
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I really don't understand dot and cross diagrams! I thought the purpose was to get a full outer shell but in ClF3, how come there are 3 bonded pairs and 2 lone pairs on the Cl? Doesn't that make 10 electrons? And in AlCl3, only 6 electrons on the Al?
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BobbJo
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Period 3 elements onwards have additional orbitals. Period 3 elements have 3d orbitals and can expand their octet and accomodate more than 8 electrons in their outer shell.

Some elements like boron can form covalent componds where the element has less than 8 electrons in outermost shell. Such as in AlCl3. These are electron deficient species.
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enigmatic17
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(Original post by alevels2020)
I really don't understand dot and cross diagrams! I thought the purpose was to get a full outer shell but in ClF3, how come there are 3 bonded pairs and 2 lone pairs on the Cl? Doesn't that make 10 electrons? And in AlCl3, only 6 electrons on the Al?
do u mean chlorine trifluoride?
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alevels2020
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(Original post by enigmatic17)
do u mean chlorine trifluoride?
yes
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enigmatic17
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for ClF3:
chlorine and fluorine have a total of 28 electrons in their outer most shell ( 7+ (7x3) ) = 28
now u place Cl in the middle of 3 fluorine atoms giving the 3 fluorine atoms a T shape ( hope u understand what I mean),
then first fill the fluorine electrons ( every fluorine atom has 7 electrons in its outermost shell then) then give one electron from chlorine to every fluorine molecule filling up the fluorine molecules with complete 8 electrons.
now there will be 4 electrons remaining on the chlorine atom, this makes up a pair of 2 lone pairs.
that's how u get 3 bond pairs ( the bonds between 3 fluorine atoms with chlorine ) and 2 lone pairs of electrons.
hope that helps good luck!
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alevels2020
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(Original post by enigmatic17)
for ClF3:
chlorine and fluorine have a total of 28 electrons in their outer most shell ( 7+ (7x3) ) = 28
now u place Cl in the middle of 3 fluorine atoms giving the 3 fluorine atoms a T shape ( hope u understand what I mean),
then first fill the fluorine electrons ( every fluorine atom has 7 electrons in its outermost shell then) then give one electron from chlorine to every fluorine molecule filling up the fluorine molecules with complete 8 electrons.
now there will be 4 electrons remaining on the chlorine atom, this makes up a pair of 2 lone pairs.
that's how u get 3 bond pairs ( the bonds between 3 fluorine atoms with chlorine ) and 2 lone pairs of electrons.
hope that helps good luck!
omg I get it now! what shape would this be though because I dont know any shapes with 3 bond pairs and 2 lone pairs?
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BobbJo
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(Original post by alevels2020)
omg I get it now! what shape would this be though because I dont know any shapes with 3 bond pairs and 2 lone pairs?
T shaped
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enigmatic17
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(Original post by alevels2020)
omg I get it now! what shape would this be though because I dont know any shapes with 3 bond pairs and 2 lone pairs?
it will have a " T " shape since one fluorine molecule will be on down and the other 2 fluorine atoms will be on the sides of chlorine atom making a T shape.
another reason for this shape is the existence of 2 lone pairs, I suppose u know that lone pairs increase the bond angle between bond pairs and lone pairs and this decreases the angle between a bond pair and another bond pair giving them shapes like these depending on my many lone pairs are present.
u would understand better if u try drawing all of these.
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alevels2020
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(Original post by enigmatic17)
it will have a " T " shape since one fluorine molecule will be on down and the other 2 fluorine atoms will be on the sides of chlorine atom making a T shape.
another reason for this shape is the existence of 2 lone pairs, I suppose u know that lone pairs increase the bond angle between bond pairs and lone pairs and this decreases the angle between a bond pair and another bond pair giving them shapes like these depending on my many lone pairs are present.
u would understand better if u try drawing all of these.
ah ok, thank you!!
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enigmatic17
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(Original post by alevels2020)
ah ok, thank you!!
no worries
good luck!
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