Shapes of Molecules Flashcards
Molecules and molecular ions come in loads of different shapes. What does this shape depend on?
The number of pairs of electrons in the outer shell of the central atom.
What are shared electrons called?
Bonding pairs.
What are unshared electrons called?
Lone pairs or non-bonding pairs.
What electron pair repels its other electron pairs more, lone or bonding pairs?
Lone pairs repel more than bonding pairs. So, the greatest angles are between lone pairs of electrons, and bond angles between bonding pairs are often reduced because they are pushed together by lone pair repulsion.
This is known as Valence-Shell Electron-Pair Repulsion Theory.
What do molecules with two electron pairs have a bond angle of and why is this?
180 degrees and have a linear shape. This is because the pairs of bonding electrons want to be as far away from each other as possible.
What are the bond angles if there are three bonding pairs of electrons?
The repulsion of the charge clouds is the same between each pair and so the bond angles are all 120 degrees.
The shape of the molecule is trigonal planar.
What shape and bond angle will you get if there are two bonding pairs of electrons and one lone pair in a molecule?
You’ll get a squished trigonal planar shape which is called non-linear. The bond angle will be a bit less than 120 degrees.
What is the shape and bond angle if there are three bonding pairs of electrons and one lone pair?
The bond angle is 107 degrees and the shape of the molecule is trigonal pyramidal.
What will happen if there are two bonding pairs of electrons and two lone pairs and what is the shape and bond angle?
The lone pair/lone pair repulsion will squish the bond angle even further.
The bond angle is 104.5 degrees and the shape of the molecules is non linear.
What shape will a molecule with five bonding pairs be?
Trigonal bipyramidal.
What does the repulsion between the bonding pairs in a trigonal bipyramidal mean?
It means that three of the atoms will form a trigonal planar shape with bond angles of 120 degrees and the other two atoms will be at 90 degrees to them.
What shape will a molecule with six bonding pairs be?
Octahedral and all of the bond angles are 90 degrees.
Give an example of molecules with two electron pairs.
Beryllium chloride
Carbon dioxide
Give an example of molecules with three electron pairs.
Aluminium chloride
Give an example of molecules with four electron pairs.
Methane
Ammonium ion
