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chemistry > chemical bonding > Flashcards

chemical bonding Flashcards

1
Q

what is an ionic bond?

A

it is the strong electrostatic force of attraction between two oppositely charged ions, formed by the transfer of electrons between the original atoms.

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2
Q

what is a covalent bond?

A

it is the strong electrostatic attraction between the positive nuclei of the two atoms and the bonding electrons shared between them.

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3
Q

what is a dative bond?

A

it is a situation where both electrons come from the same atom.

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4
Q

what is an adduct?

A

it is a chemical species containing two different similar species.

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5
Q

what is a dimer?

A

it is a chemical species consisting of 2 identical simpler species.

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6
Q

what is an expanded octet?

A

it is a case where the central atom has more than 8 valence electrons after bonding. it is only possible if the central atom has accessible vacant d orbitals. (period 3 onwards)

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7
Q

what is the first postulate of the VSEPR theory?

A

the electrons in the valence shell of the central atom will experience the least repulsion when they are as far apart from each other as possible.

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8
Q

what is the second postulate of the VSEPR theory?

A

the repulsion between electron pairs decrease in the following order: lplp repulsion > lpbp repulsion > bpbp repulsion

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9
Q

2bp on central atom, shape and angle?

A

linear, 180

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10
Q

3bp 0lp on central atom, shape and angle?

A

trigonal planar, 120

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11
Q

2bp 1lp on central atom, shape and angle?

A

bent, <120

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12
Q

4bp 0lp on central atom, shape and angle?

A

tetrahedral, 109.5

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13
Q

3bp 1lp on central atom, shape and angle?

A

trigonal pyramidal, 107

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14
Q

2bp 0lp on central atom, shape and angle?

A

bent, 104.5

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15
Q

5bp 0lp on central atom, shape and angle?

A

trigonal bipyramidal, 90, 120

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16
Q

4bp 1lp on central atom, shape and angle?

A

see saw, <90, <120

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17
Q

3bp 2lp on central atom, shape and angle?

A

T-shaped, <90

18
Q

2bp 3lp on central atom, shape and angle?

A

linear, 180

19
Q

6bp 0lp on central atom, shape and angle?

A

octahedral, 90

20
Q

5bp 1lp on central atom, shape and angle?

A

square pyramidal, <90

21
Q

4bp 2lp on central atom, shape and angle?

A

square planar, 90

22
Q

what is the third postulate of the VSEPR theory?

A

repulsion between bond pairs of electrons increases with an increase in the electronegativity of the central atom and decreases with an increase in the electronegativity of the terminal atoms.

23
Q

how are sigma bonds formed?

A

it is formed by the head-on overlap between atomic orbitals. it usually occurs between s+s, p+p and s+p orbitals. it is symmetric about the bond axis.

24
Q

how are pi bonds formed?

A

it is formed by the sideways overlap of parallel p orbitals

25
Q

what bonds does a double bond contain?

A

it contains one sigma bond and one pi bond

26
Q

why is a sigma bond stronger than a pi bond?

A

this is because there is a greater extent of overlap between the atomic orbitals in a sigma bond.

27
Q

what is the covalent character in an ionic bond?

A

it arises due to the polarisation of an anion by a highly charged cation

28
Q

how is covalent character in an ionic bond determined?

A

it is determined by the polarising power of the cation. with a higher charge density, the cation can polarise the anion to a greater extent
it is also determined by the polarisability of the anion. larger ions are more easily polarised.

29
Q

what is a non-polar bond?

A

it is where the bonded atoms have the same or similar electronegativities.

30
Q

what is a polar bond?

A

it is where one atom is more electronegative than the other. the atom which is more electronegative will carry a partial negative charge while the other atom will carry a partial positive charge.

31
Q

what is ionic character in a covalent bond?

A

the greater the difference in electronegativity between the two atoms, the more polar the covalent bond.

32
Q

what is bond energy?

A

it is the energy absorbed when one mole of a given covalent bond in a gaseous compound is broken into gaseous atoms or molecules.

33
Q

what affects covalent bond strength?

A
  1. bond order: the greater the bond order, the greater the bond energy
  2. size of the bonding atom: the smaller the atomic size, the less diffused the orbitals, the larger the extent of overlap between atomic orbitals, the stronger the covalent bond
  3. electronegativity difference: the greater the electronegativity difference, the stronger the bond polarity and hence the greater the bond strength.
34
Q

what determines the polarity of a molecule?

A

it is determined by the overall net dipole moment of the molecules. this is determined by the bond polarities and the shape of the molecule.

35
Q

how does id-id interaction arise?

A

instantaneous dipole-induced dipole interaction arises due to instantaneous dipoles for non-polar molecules. electrons are mobile and they can be displaced towards one end of the molecule, making that end partially positive. the other end will then be temp. short of electrons and so becomes partially positive. it is present between all particles and the attraction is weak.

36
Q

what factors affect the strength of id-id interactions

A

size of electron cloud: a larger electron cloud is more polarisable and hence id-id interactions are more easily formed.

surface area of contact between molecules: the greater the surface area of contact, the stronger the id-id interactions.

37
Q

how does pd-pd arise?

A

permanent dipole- permanent dipole attraction occurs between polar molecules due to the attraction between permanent dipoles in the structure. the strength of the pd-pd attraction increases with increasing overall dipole moment.

38
Q

how do hydrogen bonds arise?

A

it has to be bonded directly to very small, highly electronegative atom with lone pairs like F, O, N and the lone pairs of electrons in a neighbouring molecule can attract the partial positive charge on the H atom.

39
Q

arrange the strength of the bondings in ascending order.

A

id-id interaction < pd-pd attraction < hydrogen bonding

40
Q

what factors determine the strength of the hydrogen bond?

A

it depends on the extensiveness of hydrogen bonds (number of lones pairs of electrons and H atoms) and the polarity of the bond.

chemistry (7 decks)

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