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Chemistry > Chapter 4- Chemical bonding > Flashcards

Chapter 4- Chemical bonding Flashcards

1
Q

Resonance structures

A

When 2 or more lewis structures can be drawn OR when there is more than one possible position for a multiple pi bond

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2
Q

Resonance hybrid

A

Is the form of the molecule that is the more stable than either one of it’s resonance structure and it’s said to have delocalised bonds.

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3
Q

Examples of molecules that have resonance structures (3)

A

+ Benzene
+ Carbonate ion
+ Ozone

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4
Q

Formal charge

A

The charge that an atom would carry if ALL the bonding electrons were split equally between the 2 atoms joined by the bond.
→ FC = (No. of valence e-) - (1/2 No. of bonding e- + No. of lonepair e-)

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5
Q

The sum of the formal charge = ?

A

The charge on the ion

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6
Q

The lower the number of atoms with formal charges?

A

The more stable the structure

→ why resonance structures that have the least number of atoms carrying a FC is preferred

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7
Q

How to figure out formal charge?

A

The nuclear charge (charge on the nucleus) - the number of electrons in the the atom (bonding, non-bonding and in inner orbital)

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8
Q

Bond order

A

The average number of bonds of the different resonance structures

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9
Q

What happens to the charge carried by the atoms in a resonance structure?

A

It is also averaged

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10
Q

VSEPR

A

Valence Shell Electron Pair Repulsion

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11
Q

4 electron domains that are all bonded has the shape and bond angle of? + example

A

+ Tetrahedral
+ 109.5
E.g = Methane

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12
Q

3 electron domains are bonded and 1 lone pair has the shape and bond angle of? + example

A

+ Triangular Pyramidal
+ 107
E.g = Ammonia NH3

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13
Q

2 bonding electron domains and 2 non-bonding pairs has the shape and bond angle of? + example

A

+ Bent/ Non-linear
+ 104
E.g = Water

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14
Q

When there are 2 electron domains with NO non-bonding pair what is the shape and the bond angle? + example (not serious)

A

+ Linear
+ 180
E.g = Beryllium Chloride, CO2

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15
Q

3 electron domains bonded and NO non-bonding pair of electrons?

A

+ Trigonal Planar
+ 120
E.g = Boron Fluoride, Methanal

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16
Q

3 electron domains bonded and 1 non-bonding pair of electrons?

A

+ Non-linear (V-shaped)
+ 117
E.g = Sulfur dioxide

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17
Q

Bonding in Diamond (GIANT covalent structure)

A

+ C atom joined by 4 other
+ Tetrahedral arrangement
+ sp3 hybridisation
+ 109.5

18
Q

Bonding in Silicon dioxide (GIANT covalent structure)

A

+ Si bonded to 4 other Oxygens

19
Q

Bonding in Graphite (GIANT covalent structure)

A

+ 2 covalent network in 2 dimensions
+ only has dispersion forces betw/ the 2 sheets of C atoms = weak forces = can easily slide over e.o = lubricant
+ C bonded to 3 others forming a hexagon
+ 120 bond angle + sp2 hybridization
+ all atoms contribute one electron to the delocalised pi-bond
+ Delocalised electrons allow it to conduct electricity in 2D

20
Q

C60/ Buckminsterfullerene/ Fullerene (GIANT covalent structure)

A

+ Spherical mol.
+ made of 5 and 6 membered C ring
+ C bonded by sigma-bond to 3 other carbons
+ sp2 hybridization
+ LITTLE delocalization of unpaired electrons = cuz surface of sphere = not planar → electrons can’t easily flow from one C60 to the next

21
Q

How is the electrical conductivity of Fullerene?

A

Better than diamond but worse than graphite

22
Q

What species does C60 behave as?

A

+ electron deficient mol. that readily accepts electrons from reducing agents to form anions with a variety of charges

23
Q

What type of reactions do fullerene undergoe?

A

Addition reactions

24
Q

Unlike diamond = fullerenes are molecular so what properties do they have that differ from graphite and diamond?

A

+ Dissolve in non-polar solvent

+ low m.p

25
Q

Graphene

A

2D material = single sheet of graphite structure

26
Q

Delocalised bonds

A

When sideways interactions of p-orbitals to form a pi-bond can involve more than 2 atoms → p-orbitals can extend over more than 2 nuclei so electrons are hared by a number of atoms

27
Q

Why does delocalization make the molecule more stable?

A

It gives the species a lower potential energy than it would if it was composed of normal double and single bonds

28
Q

How is Stratospheric Ozone formed?

A

+ Photodissociation of O2 molecules caused by UV light from sun to produce O ATOMS.

29
Q

Mechanism for Photodissociation of O2

A

O2 (g) → (UV light) 2O• (g)
Oxygen atoms are v. reactive and combine with O2 mol. to form Ozone:
O2 (g) + O• (g) → O3 (g)

30
Q

UV light also causes photodissociation of Ozone itself. State the mechanism.

A

O3 (g) → (UV light) O2 + O• (g)
O3 (g) + O• → 2O2 (g)
This results in an equilibrium concentration of Ozone in the Stratosphere

31
Q

Is the UV absorbed by Ozone of longer or shorter wavelength than absorbed by Oxygen molecule?

A

Longer wavelength and less energetic → still v. damaging and increases risk of skin cancer in human

32
Q

CFCs (Chlorofluorocarbons) undergo photo dissociation to yield chlorine atoms. What do chlorine atoms do?

A

Catalyse the decomposition of ozone

33
Q

NO also catalyses decomp of ozone. How is NO produced?

A

Combination of Oxygen and Nitrogen in air at high temp of jet engines

34
Q

5 regions of high electron density gives what shape according to VSEPR and what bond angle?

A

Trigonal bipyramidal

90° and 120°

35
Q

5 e- domains w/ 1 non-bonding pair = shape and bond angles

A

saw horse

90° and 117°

36
Q

5 e- domains w/ 2 non-bonding pair = shape and bond angles

A

T-shaped

90°

37
Q

5 e- domains w/ 3 non-bonding pair = shape and bond angles

A

Linear

180°

38
Q

6 regions of high electron density gives what shape according to VSEPR and what bond angle?

A

Octahedral

90°

39
Q

6 e- domains w/ 1 non-bonding pair = shape and bond angles

A

Square pyramid

88°

40
Q

6 e- domains w/ 2 non-bonding pair = shape and bond angles

A

Square planar

90°

41
Q

Hybridization

A

The combining of atomic orbitals to form new orbitals of equal energy

Chemistry (10 decks)

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