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Chemistry > 4.3 Covalent Structures > Flashcards

4.3 Covalent Structures Flashcards

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1
Q

What’s a co-ordinate bond?

A

Where both shared electrons come from the same atom

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2
Q

What is a Lewis structure?

A

A diagram that represents the structure of a covalent bond

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3
Q

What is the symbol for a dative bond?

A

An arrow

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4
Q

Why do coordinate bonds happen?

A

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

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5
Q

What is the VSEPR theory?

A

The shape of a molecule is determined by repulsion between electron domains

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6
Q

Why are molecules certain shapes?

A

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

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7
Q

Why do lone pairs repel more?

A

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

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8
Q

Which electrons repel - from the most to the least

A

Lone pair - lone pair > lone pair - bonding pair

> bonding pair - bonding pair

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9
Q

What can you say about linear molecules?

A

There are 2 electron domains
180 degree bond angles
Eg. BeCl2

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10
Q

What can you say about trigonal planar molecules?

A

There are 3 electron domains
120 degree bonding angles
Eg. BF3

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11
Q

What can you say about tetrahedral molecules?

A

There are 4 electron domains
Bond angle of 109.5 degrees
Eg. CH4

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12
Q

What shape is NH3?

A

Pyramidal

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13
Q

What determines the polarity of a molecule?

A

The polar bonds that it contains

Orientation of the bonds (shape)

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14
Q

If the bonds are of ………… Polarity and are arranged ……………. The charges will cancel each other out and be neutral

A

If the bonds are of equal polarity and are arranged symmetrically the charges will cancel each other out and be neutral

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15
Q

What is the net dipole moment?

A

When the molecule contains bonds of different polarity or they are not symmetrically arranged then the dipoles will not cancel each other out

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16
Q

What is resonance?

A

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

17
Q

What does benzene look like?

A

There are 6 carbons in a hexagonal ring with alternate double bonds and each is attached to a hydrogen in a trigonal planar arrangement

18
Q

What can you say about graphite?

A

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

19
Q

What can you say about diamond?

A 
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
20
Q

What can you say about Fullerene?

A 
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
21
Q

What can you say about graphene?

A 
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
22
Q

What can you say about silicon and silicon dioxide?

A 
Four  valence electrons
Insoluble in water
High melting point 
Doesn't conduct electricity 
Giant covalent structure 
The oxygen forms bridges between the silicon atoms
23
Q

Why is graphite a good electrical conductor but diamond isn’t?

A

Graphite has a delocalised electrons which are mobile and carries charge, however in diamond all of the electrons are held in covalent bonds

24
Q

Which of the following are polar molecules?

PH3. CF4. HCN. BECl2. C2H4. CIF. F2. BF3

A

Yes. No. Yes. No. No. Yes. No. No

25
Q

How many electrons domains are in a tetrahedral shape

A

4

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