define the basic assumptions of VSPER theory
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Answered by
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VSEPR Theory Definition
This theory is very useful in predicting the
geometry or shape of a number of
polyatomic molecules or ions of non-
transition elements.
This theory was proposed for the first
time by Sidgwick and Powell in 1940 and
developed by Gillespie and Nyholm in
1957 . According to this theory
“The shape of a given species ( molecule
or ion ) depends on the number and nature
of electron pairs surrounding the central
atom /ion of the species .”
VSEPR Theory Examples
1. Shape of molecules /ions with central
atom surrounded by two atoms :
Type: AB 2
Example of such molecule is BeF2 . They
have a linear shape. A is the central atom
and B , the bonded atoms. Only sigma
bonding is present in such molecules, with
no lone pair on the central atom.
F -- --- -- --- - Be - -- --- -- - F
2. Shape of molecules /ions where central
atom is surrounded by three atoms/ ions:
Type: AB 3 ( 3bp ) and AB 2 ( 2 bp and 1 lp)
Example of such molecule is BF3 , GaCl 3
etc with three bonding electron pairs and
SnCl2 , PbCl 2 etc . with two bonding pairs
and one lone pair. They have trigonal
planar or angular or V - shape.
3. Shape of molecules /ions whose central
atom /ion has four electron pairs :
Types: AB 4 (4 bps) , AB 3 (3 bps and 1 lp),
AB2 ( 2 BPs and 2 lps ) and AB (3 lps and
1bp )
Example : AB 4 - CH4 , SiCl4 , etc . They have
a tetrahedral shape. The bond angle is
109.5 o .
4. Shape of molecule of type: AB 5 ( 5
bonding pairs )
Example : PCl5 , PF5 , etc . They have
trigonal bi pyramidal shape .
VSEPR Theory Definition
This theory is very useful in predicting the
geometry or shape of a number of
polyatomic molecules or ions of non-
transition elements.
This theory was proposed for the first
time by Sidgwick and Powell in 1940 and
developed by Gillespie and Nyholm in
1957 . According to this theory
“The shape of a given species ( molecule
or ion ) depends on the number and nature
of electron pairs surrounding the central
atom /ion of the species .”
VSEPR Theory Examples
1. Shape of molecules /ions with central
atom surrounded by two atoms :
Type: AB 2
Example of such molecule is BeF2 . They
have a linear shape. A is the central atom
and B , the bonded atoms. Only sigma
bonding is present in such molecules, with
no lone pair on the central atom.
F -- --- -- --- - Be - -- --- -- - F
2. Shape of molecules /ions where central
atom is surrounded by three atoms/ ions:
Type: AB 3 ( 3bp ) and AB 2 ( 2 bp and 1 lp)
Example of such molecule is BF3 , GaCl 3
etc with three bonding electron pairs and
SnCl2 , PbCl 2 etc . with two bonding pairs
and one lone pair. They have trigonal
planar or angular or V - shape.
3. Shape of molecules /ions whose central
atom /ion has four electron pairs :
Types: AB 4 (4 bps) , AB 3 (3 bps and 1 lp),
AB2 ( 2 BPs and 2 lps ) and AB (3 lps and
1bp )
Example : AB 4 - CH4 , SiCl4 , etc . They have
a tetrahedral shape. The bond angle is
109.5 o .
4. Shape of molecule of type: AB 5 ( 5
bonding pairs )
Example : PCl5 , PF5 , etc . They have
trigonal bi pyramidal shape .
Answered by
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Atoms in a molecule are bound together by electron pairs .
More than one set of bonding pairs of electrons may bind any two atoms together (multiple bonding).
Some atoms in a molecule may also possess pairs of electrons not involved in bonding.
The bonding pairs and lone pairs around any particular atom in a molecule adopt positions in which their mutual interactions are minimized .
Electron pairs are negatively charged and will get as far apart from each other as possible.
More than one set of bonding pairs of electrons may bind any two atoms together (multiple bonding).
Some atoms in a molecule may also possess pairs of electrons not involved in bonding.
The bonding pairs and lone pairs around any particular atom in a molecule adopt positions in which their mutual interactions are minimized .
Electron pairs are negatively charged and will get as far apart from each other as possible.
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