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Chemistry Y12 > P- Bonding > Flashcards

P- Bonding Flashcards

1
Q

What is a coordinate/ dative covalent bond?

A

A shared pair of e- w/ both e- SUPPLIED by one atom

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2
Q

Electronegativity

A

The power of an atom to attract the pair of e- in a covalent bond

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3
Q

What is the way of drawing atoms showing e- w/o shells called?

A

Lewis structures

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4
Q

What is electronegativity measured in?

A

Pauling scale (0-4)

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5
Q

Describe the trend in electronegativity in the periodic table.

A
  • ↓ down the group
    ∵ shielding ↑
  • ↑ across the period
    ∵ nuclear charge ↑ (↑ + charge to pull e- )
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6
Q

What is the atom that accepts the e- pair (slightly positive end of the molecule) called?

A

Electron deficient (/ delta positive)

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7
Q

What is the bond between 2 atoms with an electronegativity difference?

A

Polar (covalent) bond

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8
Q

How do we know whether 2 elements form covalent or ionic bonds?

A

electronegativity diff. < 1.7 – covalent
> 1.7 – ionic

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9
Q

Octet rule

A

atoms are most stable when they have 8 outer e-
(esp. if they are in bonds)

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10
Q

Why are molecular structures poor conductors of electricity?

A
  • they have an overall neutral charge
  • x charged particles to carry charge
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11
Q

How are coordinate covalent bonds represented in a diagram?

A

Arrow pointing towards atom accepting e- pair

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12
Q

Condition needed for the formation of a dative covalent bond

A

lone pair + incomplete octet –> dative covalent bond

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13
Q

What is the name of the compound called when some very reactive molecules (eg. AlCl3) reacts with itself?

A

Dimer- ↑ reactive

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14
Q

What is a dipole?

A

A covalent bond whose ends have opp. partial charges.

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15
Q

Why is F more electronegative than Cl?

A
  • smaller atom
  • shared e- closer to nucleus when covalent bond forms
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16
Q

Starter: How does sodium conduct electricity?

A
  • delocalised e-
  • move & carry charge THROUGH the structure
  • when potential difference is applied
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17
Q

What are intermolecular forces?

A

Weak forces of attraction between 2 molecules

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18
Q

Give one unusual physical property molecules with H bonds have compared to molecules that don’t.

A

Molceules w/ H bonds- ↑ bp

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19
Q

2 conditions needed for H bonding

NEEDS BOTH!!!

A
  1. N, O or F directly bonded to a H atom
  2. Lone pair on N, O or F atom
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20
Q

Examples where H bonding is seen

A
  1. Ammonia (NH3)
    • N is v. electronegative + has 1 lone pair
  2. Water
    • O has 2 lone pairs
  3. Alcohol- O-H
  4. Carboxylic acid- O-H
  5. Amine- N-H
  6. Protein- N-H
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21
Q

Why does ice have a low density?

A
  • maximises amount of H bonds between molecules
  • open hexagonal structure w/ large spaces within crystal
  • melting–> liquid occupies ↓ space –> ↑ dense
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22
Q

Why is a DNA molecule helical?

A
  • C=O bonds in long chains
  • H atoms + electronegative O atom –> H bond
  • molecule spirals

INTRAmolecular H bonds- attraction between H & electronegative atom on the SAME MOLECULE

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23
Q

What kind of substances are affected by Van der Waals forces?

A

Atoms & molecules (x ions) apart from diamond & silicon dioxide (SiO2)

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24
Q

How is a temporary dipole formed?

A
  • e- cloud in constant motion –> temp dipole when more at one pole
  • attraction between 2 molecules induces dipole on the other molecule–> VdW
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25
Q

Factors increasing strength of VdW forces

A
  1. ↑ e- cloud
  2. ↑ Ar of atoms/ Mr of compounds
  3. s.a.
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26
Q

How does shape of a molecule affect its boiling point?

A
  • straight chains have ↑ bp (than spherical)
    ∵ ↑ s.a. for VdW forces
    ↑ interactions + stronger
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27
Q

Factors determining bp

A
  1. Mr
  2. Are there dipole-dipole/ H bonds as well as VdW?
  3. Shape

**H bonds= strongest IM–> high bp (eg. water- unusually high bp)

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28
Q

What is ‘absolute zero’?

A

0 K- everything is solid

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29
Q

Explain why temp of water doesn’t change during boiling/ melting.

A

Melting- energy is used to break SOME of the H bonds
Boiling- ALL H bonds
– x IM forces in gas ∵ all H bonds broken when boiling

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30
Q

Explain what energy transferred is used for during melting of a substance.

A

To overcome SOME forces holding atoms/ ions/ molecules in proximity

31
Q

Explain what energy transferred is used for during boiling of a substance.

A

To overcome ALL forces between atoms/ ions/ molecules in proximity
∴ x IM forces in gases

32
Q

What is a crystal?

A

A substance in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating three-dimensional patterns.

  • most crystals are solids
33
Q

What are the forces to overcome when a molecular crystal is heated?

A
  1. the strongest type of IM force present
  2. any other IM forces (Van der Waals, permanent dipole-dipole)
34
Q

What are the forces to overcome when an ionic crystal is heated?

A

Ionic bonds

x IM forces!!

35
Q

What are the forces to overcome when a metallic crystal is heated?

A

Metallic bonds

x IM forces!!

36
Q

What are the forces to overcome when a macromolecular crystal is heated?

A

Covalent bonds

x IM forces!!

37
Q

Explain why hexane is a liquid at room temp while butane is a gas.

A
  • hexane- larger molecule
  • ∴ ↑ e-
  • ↑ VdW between molecules
38
Q

Explain why covalent molecules are gases, liquids, or solids with low melting points.

A
  • covalent bonds only between the 2 atoms they bond
  • small attraction between individual molecules
39
Q

Phosphorus (P4) has a mp of 317K while Sulfur (S8) has a mp of 386K.

Explain this difference in terms of bonding.

A
  • ↑ VdW
  • ∵ ↑ e-
40
Q

Co-ordination no.

A

no. of bonds around a central atom

41
Q

What kind of bond has the highest repulsion?

A

lone pair-lone pair
– to ↓ repulsion, outer e- spread out as far apart in space as poss.

42
Q

What is VSEPR?

A

Valence shell electron repulsion theory

43
Q

Name + bond angle w/ 2 bonding pairs

A

Linear- 180

44
Q

Name + bond angle w/ 3 bonding pairs

A

Trigonal planar- 120

45
Q

Name + bond angle w/ 4 bonding pairs

A

Tetrahedral- 109.5
– achieved thru 3D!! (max 90 if 2D)

46
Q

Name + bond angle w/ 5 bonding pairs

A

Trigonal bipyramidal- 90 &120

47
Q

Name + bond angle w/ 6 bonding pairs

A

Octahedral- 90

48
Q

How would the bond angle change when there are lone pairs on a tetrahedral (4 co-ordinate) shaped molecule?

A

Take off 2.5 for every lone pair

49
Q

How would the bond angle change when there are lone pairs on a linear/ trigonal planar shaped molecule?

A

x affected by lone pairs

50
Q

Explain the shape of an ammonia (NH3) molecule

A
  • trigonal pyramid- 107
  • bonding pairs attracted to H as well as N
  • vs lone pair only attracted to N
  • ∴ pulled closer
  • H-N-H angle ↓
51
Q

What is different in bonding between a macromolecular and molecular crystal?

A

Molecular:
- strong covalent bonds between atoms
- weaker intermolecular forces between molecules

vs

Macromolecular:
- all atoms are covalently bonded

52
Q

Do ionic compounds conduct electricity?

A

yes when molten
- ions x free to move in solids
- free to move & carry charge when separated

53
Q

Are ionic compounds soluble?

A

yes
- ∂+ & ∂- ends of H2O attracted to ions

54
Q

Why are ionic compounds brittle?

A
  • layers slide–> same charges next to each other
  • repulsion cracks crystal
55
Q

Melting points of monatomic substances

A

v. low
- v. weak forces between ATOMS

56
Q

Do monatomic substances conduct?

A

no
- atoms are NEUTRAL
- x mobile charged particles

57
Q

Why are metallic compunds strong?

A
  • layers can slide
  • while maintaining metallic bonding
58
Q

Why does graphite conduct electricity?

A
  • delocalised e- free to move
  • BETWEEN LAYERS
59
Q

Why is graphite brittle?

A
  • weak IM forces between layers (graphene)
  • can slide

(pi-pi stacking interactions)

60
Q

Describe the structure of ice

A
  • 3D open structure
  • held tgt by covalently bonded H2O molecules (2 H bonds)
  • each O bonded to 4 H atoms
  • tetrahedral shape
61
Q

mp & bp of ice

A

low
- weak forces between H2O molecules

62
Q

Why does ice have a lower density than water?

A
  • molecules in a lattice ∵ H bonds
  • vs water molecules closer ∵ x in lattice
63
Q

Why is a dative covalent bond represented by an arrow?

A

to show both e- come from the same atom

64
Q

Why is Br in p block?

A

OUTER e- in p orbital

65
Q

Explain why the bond angles in CH4 are all 109.5.

A
  • so that 4 bond pairs can be
  • as far apart as poss.
  • as they repel equally
66
Q

How do HCl and HF differ in appearance when drawn?

A
  • bigger arrow showing dipole in HF ∵ bigger dipole
  • draw lone pairs on for F for H bonding
  • ∵ lone pair= one of the conditions for H bonding!!!
67
Q

What does VSEPR mean?

A
  • e- pairs repel
  • move as far apart in space as poss.
  • MINIMISE REPULSION

l-l > l-b > b-b

68
Q

Describe briefly strucutre of diamond

A
  • rigid
  • tetrahedral
  • lattice
69
Q

Describe briefly structure of graphite

A
  • planar
  • hexagonal layered structure
  • layers held by weak IMF
70
Q

What’s the shape with 2 lone pairs and 3 bond pairs?

A

T-shape/ trigonal planar

71
Q

Formula of hydrogencarbonate ion

A

HCO3-

72
Q

Formula of nitrate ion

A

NO3-
2 single bonds + one double bond

73
Q

Give 2 examples of polar molecules

A
  1. Urea
    • lots of polar bonds
  2. Ethanol
    ∵ has both polar & non-polar ends\
    ∴ can dissolve both polar & non-polar substances

Chemistry Y12 (33 decks)

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