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Chemical Bonding Flashcards

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1
Q

What is an ionic bond?

A

Electrostatic attraction between cations and anions.

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2
Q

What is lattice energy?

A

Energy released when one mole of an ionic crystalline solid is formed from its constituent gaseous ions. Indicative of ionic bond strength.

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3
Q

What is lattice energy proportional to?

A

|Lattice energy| = |(q+ x q-)/(r+ x r-)|

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4
Q

What are the physical properties of ionic compounds?

A
  1. High melting and boiling points due to strong bonds
  2. Soluble in polar solvents but insoluble in non-polar solvents
  3. Conducts electricity in aqueous or molten state but not in solid state due to ions being able to move around to act as mobile charge carriers.
  4. Hard and brittle as hard blows brings ions of like charges opposite one another, strong attraction becoming strong repulsion.
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5
Q

What is a covalent bond?

A

Electrostatic attraction between shared electrons and positively charged nuclei.

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6
Q

What are the physical properties of giant covalent compounds?

A
  1. High melting and boiling points due to strong bonds
  2. Insoluble
  3. Not conductors except for graphite
  4. Hard. Graphite is brittle due to its layered structure
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7
Q

What are the physical properties of simple covalent compounds?

A
  1. Low melting and boiling points due to weak intermolecular forces of attraction between molecules
  2. Insoluble in polar solvents but soluble in non-polar solvents
  3. Not conductors except for when it ionises in water when aqueous
  4. Soft
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8
Q

What is a metallic bond?

A

Electrostatic attraction between a lattice of positive ions and delocalised electrons.

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9
Q

What are the factors affecting the strength of a metallic bond?

A
  1. Number of valence electrons available. More electrons, stronger bonds.
  2. Charge of cations. Higher charge, stronger bonds.
  3. size of cations. Smaller size, higher charge density, greater electrostatic attraction for delocalised electrons, stronger bonds.
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10
Q

What are the physical properties of metallic compounds?

A
  1. High melting and boiling points due to strong bonds
  2. Insoluble
  3. Conducts electricity in any state
  4. Hard and malleable as positive ions can glide over each other easily
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11
Q

What is a dative covalent bond?

A

A shared pair of electrons provided by only one bonding atom, represented by an arrow. One atom should have a lone pair of electrons, while the other atom or ion must have a vacant, low lying orbital to accept the electrons.

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12
Q

2 regions of electron density:

A

Geometry: Linear

Bond angle: 180°

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13
Q

3 regions of electron density:

A

Geometry: Trigonal planar
Bond angle: 120°
Shape and bond angle with 1 lone pair: Bent, <120°

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14
Q

4 regions of electron density:

A

Geometry: Tetrahedral
Bond angle: 109.5°
Shape and bond angle with 1 lone pair: Trigonal pyramidal, ~107°
Shape and bond angle with 2 lone pairs: Bent, ~105°

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15
Q

5 regions of electron density:

A

Geometry: Trigonal bipyramidal
Bond angle: 120°, 90°
Shape and bond angle with 1 lone pair: See saw, NA
Shape and bond angle with 2 lone pairs: T shape, 90°
Shape and bond angle with 3 lone pairs: Linear, 180°

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16
Q

6 regions of electron density:

A

Geometry: Octahedral
Bond angle: 90°
Shape and bond angle with 1 lone pair: Square pyramidal, <90°
Shape and bond angle with 2 lone pairs: square planar, 90°

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17
Q

Why do different electron pairs exert different repulsions? (lone-lone > lone-bond > bond-bond)

A

The closer electron pairs are to the central atom, the greater the repulsion. Lone pair exerts greater repulsion than bond pairs because lone pairs are only attracted by one nucleus and is hence closer to the central atom, compared to the bond pair that is attracted by two nuclei. Thus bond angles deviate more greatly from the predicted angle as number of lone pairs increases.

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18
Q

How is a polar covalent bond formed?

A

When two atoms of different electronegativities form a covalent bond, the electron pair is not equally shared, and partial charges arise. The greater the difference in electronegativity, the greater the dipole moment and the more polar the bond.

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19
Q

What is overall dipole moment?

A

Vector sum of all the bond dipole moments.

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20
Q

How to find out if a molecule is polar:

A
  1. Draw dot and cross diagram
  2. See if there are polar bonds
  3. See if bond dipole moments cancel out vectorially
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21
Q

How to find out interactions between molecules:

A
  1. Draw dot and cross diagram
  2. Use VSEPR to find the shape
  3. Find out if molecule is polar or non-polar
  4. Find out the interactions between the molecules
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22
Q

What are the 3 types of intermolecular forces?

A
  1. Instantaneous dipole induced dipole interactions (id-id)
  2. Permanent dipole permanent dipole interactions (pd-pd)
  3. Hydrogen bonds
23
Q

What are the characteristics of id-id interactions?

A

Short-lived as electrons keep moving and dipoles constantly form and disappear, weak, present in all molecules.

24
Q

How do id-id interaction arise?

A

Electrons in a particle is always moving, thus electron density can be unsymmetrical, resulting in an instantaneous dipole. This can induce dipoles in neighbouring particles and can cause attraction.

25
Q

What are the factors affecting strength of id-id interactions?

A
  1. Number of electrons

2. Surface area of molecule (straight-chained isomers or branched isomers)

26
Q

How does the number of electrons affect strength of id-id interactions?

A

The greater the number of electrons, the larger the electron cloud, the more easily it is polarised, the greater the ease of forming instantaneous dipoles and hence induced dipoles.

27
Q

How does surface area affect strength of id-id interactions?

A

For molecules with same number of electrons, as surface area for molecular interactions increases, strength of id-id interactions increases.

28
Q

How do pd-pd interactions arise?

A

Polar molecules have permanent dipoles and align such that the more positive side of one molecule is near the more negative side of another molecule, and this gives rise to electrostatic forces of attraction.

29
Q

How do hydrogen bonds arise?

A

Hydrogen atom is bonded to a highly electronegative atom with lone electron pairs, principally F, O or N. these atoms cause H to have a high partially positive charge, allowing it to form strong attractions with a lone pair of electrons on another molecule.

30
Q

What are the 2 criteria for hydrogen bonding?

A
  1. A hydrogen atom covalently bonded to F, O or N.

2. A lone pair of electrons on a F, O or N atom in a neighbouring molecule.

31
Q

What are the 2 ways hydrogen bonds affect physical properties?

A
  1. Strength of hydrogen bonds

2. Extensiveness of hydrogen bonding

32
Q

How do you calculate the extensiveness of hydrogen bonding?

A

in a molecule, find the number of lone pair of electrons and the number of H atoms. The lowest number between those two is the average number of hydrogen bonds in that molecule.

33
Q

How does hydrogen bonding affect the boiling points of different molecules?

A

With more extensive hydrogen bonding, more hydrogen bonds need to be broken during boiling, more energy is thus required.
Hydrogen bonds are stronger than id-id and pd-pd interactions, thus for molecules with the same number of electrons, more energy is required to break down the bonds in the molecule with hydrogen bonds, thus its bp will be higher.
When both molecules have same number of electrons and hydrogen bonds, the more polar a bond is, the stronger the hydrogen bond is, meaning more energy is required to overcome it.

34
Q

How does hydrogen bonding affect the structure of ice/

A

In ice, one oxygen atom is tetrahedrally bonded to 4 H atoms, two by covalent bonds, two by hydrogen bonds, enabling ice to form a rigid, open, 3d network. It occupies a larger volume and hence ice is less dense tha water.

35
Q

How does hydrogen bonding cause dimerisation of carboxylic acids?

A

The acids can be bonded to each other through hydrogen bonding. However, in aqueous solutions, they are n=bonded to water molecules instead.

36
Q

How does hydrogen bonding affect boiling point and solubility of 2-xxx and 4-xxx isomers?

A

Due to formation of hydrogen bonds in 2-xxx, less sites are available for hydrogen bonding with other 2-xxx molecules, thus intermolecular hydrogen bonding is less extensive than 4-xxx molecules, and requires less energy to overcome.
2-xxx also forms fewer hydrogen bonds with water molecules compared to 4-xxx due to intramolecular hydrogen bonds, Thus 2-xxx is less soluble.

37
Q

What are the three cases for dissolution?

A
  1. Simple molecules with the same IMF mix well
  2. Ionic solids tend to dissolve in water
  3. A chemical reaction occurred
38
Q

Why do simple molecules with the same IMF mix well?

A

Energy absorbed from breaking the interactions between solute molecules or solvent molecules can be compensated by energy energy releases from forming the same interaction between solute and solvent molecules.

39
Q

Why do ionic solids tend to dissolve in water?

A

The crystal lattice of an ionic compound must be broken down and requires a large input of energy. There is also a large amount of energy released from ions forming strong ion-dipole interactions with polar water molecules. Energy released can compensate for energy absorbed.

40
Q

How do chemical reactions allow for dissolution?

A

The products may form favourable interactions with the solvent.

41
Q

When does covalent bonding occur?

A

When valence orbitals overlap. Orbitals are either both singly occupied or one is filled and the other is empty.

42
Q

When is a σ bond formed?

A

When two orbitals overlap head on. Electron density is concentrated between the nuclei.

43
Q

When is a π bond formed?

A

When two orbitals overlap collaterally. Electron cloud is above and below the nuclear axis but with zero density along the axis.

44
Q

Number of bonds and the types of bonds:

A

Single bond: σ bond only
Double bond: 1 σ bond, 1 π bond
Triple bond: 1 σ bond, 2 π bonds

45
Q

Why is σ bond stronger than π bond?

A

Head to head overlap in σ bonds have a greater degree of overlap than side to side overlap in π bonds.

46
Q

What is bond length?

A

The distance between the nuclei of two bonded atoms.

47
Q

How does strength of covalent bond affect bond length?

A

The stronger the covalent bond, the shorter the bond length.

48
Q

What is covalent bond strength?

A

The average energy absorbed when one mole of a particular bond is broken in the gaseous state.

49
Q

What affects covalent bond strength?

A
  1. Number of bonds between atoms
  2. The effectiveness of overlap of the orbitals
  3. The differences in electronegativities of the bonding atoms
50
Q

How does number of bonds between atoms affect covalent bond strength?

A

An increase in number of bonds increases the number of shared electrons between the two atoms, increasing electrostatic attraction between the bond pairs and the nuclei.

51
Q

How does the effectiveness of overlap of the orbitals affect covalent bond strength?

A

The more effective the orbital overlap (the less diffuse the orbital is), the stronger the bond.

52
Q

How do differences in electronegativities of bonding atoms affect covalent bond strength?

A

The greater the difference in electronegativities, the more polar the covalent bond, the greater the electrostatic attraction between the partial charges, the stronger the bond.

53
Q

What affects the polarising power of a cation?

A

The charge density (charge/volume). The higher the charge and smaller the cation, the stronger its polarising power.

54
Q

What affects the polarisability of an anion?

A

Charge and size. Electron clouds of larger anions are easier to distort.

Chemistry (8 decks)

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