2.2.2 Shapes Of Simple Molecules + Ions Flashcards
What’s a valence shell electron
Outer electron
How can pairs of electrons be shared
Covalent bond
What are unshared pairs of electrons called
Lone pairs
Why are electrons as far apart from each other as possible
They’re all negatively charged so will repel
What electrons pairs repel the most
Why
Lone pairs
Closer to nucleus than bonding pairs
What do we use to show the bond is pointing towards us
A wedge
What do we use to show the bond is pointing away from us
A dashed line
What does the shape of a covalent molecule depend on
The type + number of electron pairs that surround the central atom
6 rules to help work out number of pairs
- Find central atom in chemical formula
- Work out number of outer shell electrons (group number)
- Add to this number the number of atoms bonded to central atom
- If it’s an ion, + ions take away charge and - ions add charge
- Divide answer by 2 to find no. Of electron pairs
- Can then work out number of bonding pairs/Lone pairs
What’s the shape and bond angles of a molecule with 2 bonding pairs
E.g BeCl2
Shape - linear
Bond angles - 180*
What’s the shape and bond angles of a molecule with 3 bonding pairs
E.g BF3
Shape - trigonal planar
Bond angles - 120*
What’s the shape and bond angles of a molecule with 4 bonding pairs
E.g CH4
Shape - tetrahedral
Bond angles - 109.5*
What’s the shape and bond angles of a molecule with 5 bonding pairs
E.g PCl5
Shape - trigonal bipyramidal
Bond angles - 120* + 90*
What’s the shape and bond angles of a molecule with 6 bonding pairs
E.g SF6
Shape - octahedral
Bond angles - 90*
For a negative ion, where has the extra electron come from
A metal
For a positive ion, what has an electron been lost to
A non-metal
What are the 4 radicals we need shapes + bond angles of
What are they
Carbonate - trigonal planar - 120*
Nitrate - trigonal planar - 120*
Sulfate - tetrahedral - 109.5*
Sulfur trioxide - trigonal planar - 109.5*
What do some molecules have that will affect the shape of them
Lone pairs
What is the greatest and least electron repulsion
Least Bonded pair + bonded pair
Bonded pair + lone pair
Most Lone pair + lone pair
What’s a lone pair closer due to do it’s greatest repulsion
The nucleus
What’s the shape and bond angles of a molecule with 3 bonding pairs and 1 lone pair
E.g
Shape - pyramidal
Bond Angles - 107*
E.g ammonia, NH3
Why is a pyramidal molecule 107, slightly reduced from 109.5
Due to the lone pairs repelling more
What’s the shape and bond angles of a molecule with 2 bonding pairs and 2 lone pairs
E.g
Shape - bent/ non-linear
Bond angles - 104.5*
E.g water, H20
What geometry are both the molecules with lone pairs based on
Tetrahedral geometry
What do all electrons do
Repel
