4.3 Covalent Structures Flashcards
What’s a co-ordinate bond?
Where both shared electrons come from the same atom
What is a Lewis structure?
A diagram that represents the structure of a covalent bond
What is the symbol for a dative bond?
An arrow
Why do coordinate bonds happen?
Molecules that have incomplete octets are electron deficient which means they can accept an electron pair from a molecule with a lone pair - this creates a coordinate compound
What is the VSEPR theory?
The shape of a molecule is determined by repulsion between electron domains
Why are molecules certain shapes?
The bonding pairs and the lone pairs around the central ion all repel each other until they reach minimum energy - but the lone pair repels more
Why do lone pairs repel more?
Because they have a higher concentration of charge than the bonding pairs because they aren’t shared between 2 atoms which means they have more repulsion
Which electrons repel - from the most to the least
Lone pair - lone pair > lone pair - bonding pair
> bonding pair - bonding pair
What can you say about linear molecules?
There are 2 electron domains
180 degree bond angles
Eg. BeCl2
What can you say about trigonal planar molecules?
There are 3 electron domains
120 degree bonding angles
Eg. BF3
What can you say about tetrahedral molecules?
There are 4 electron domains
Bond angle of 109.5 degrees
Eg. CH4
What shape is NH3?
Pyramidal
What determines the polarity of a molecule?
The polar bonds that it contains
Orientation of the bonds (shape)
If the bonds are of ………… Polarity and are arranged ……………. The charges will cancel each other out and be neutral
If the bonds are of equal polarity and are arranged symmetrically the charges will cancel each other out and be neutral
What is the net dipole moment?
When the molecule contains bonds of different polarity or they are not symmetrically arranged then the dipoles will not cancel each other out
What is resonance?
When instead of being confined to one position the electrons are delocalised and there for can move to new bonding positions which give the ion greater stability
What does benzene look like?
There are 6 carbons in a hexagonal ring with alternate double bonds and each is attached to a hydrogen in a trigonal planar arrangement
What can you say about graphite?
Each carbon atom is bonded to three others
Sheets of hexagons layered on top of each other
Bond angles of 120 degrees
Layers are held together by weak London dispersion forces
Doesn’t conduct heat very well
Conducts electricity well (delocalised electron)
High melting point (covalent bonds)
Can be used as a dry lubricant
What can you say about diamond?
Each carbon is bonded to 4 others It's tetrahedrally arranged Bond angles of 109.5 degrees Doesn't conduct electricity Conducts heat (conduction) Very high melting point (covalent bonds) Giant structure Transparent and lustrous
What can you say about Fullerene?
Sphere of 60 carbon atoms 12 pentagons and 20 hexagons Each carbon is bonded to 3 others It ha a fixed formula (not a giant molecule) Semi conductor (electron mobility) Doesn't conduct heat Can't be used as a lubricant
What can you say about graphene?
Single sheet of graphite Covalent lay bonded to 3 carbon atoms Bonds angles of 120 degrees Best thermal conductor on earth High melting point Almost transparent Can be used for nanotubes
What can you say about silicon and silicon dioxide?
Four valence electrons Insoluble in water High melting point Doesn't conduct electricity Giant covalent structure The oxygen forms bridges between the silicon atoms
Why is graphite a good electrical conductor but diamond isn’t?
Graphite has a delocalised electrons which are mobile and carries charge, however in diamond all of the electrons are held in covalent bonds
Which of the following are polar molecules?
PH3. CF4. HCN. BECl2. C2H4. CIF. F2. BF3
Yes. No. Yes. No. No. Yes. No. No
How many electrons domains are in a tetrahedral shape
4
