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CLS3003-B: Chemistry (Semester 1) > L10 - Chemical Bonding (4) > Flashcards

L10 - Chemical Bonding (4) Flashcards

1
Q

What is an Ionic Bond?

A

A bond that is the result of an electrostatic attraction between two oppositely charged ions.

(+ve ions from metals, -ve ions from non-metals)

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2
Q

What is a Covalent Bond?

A

A bond between two atoms, in which the two atoms share a pair of electrons.

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3
Q

What is a Dative Covalent Bond?

A

A bond formed when one atom provides both electrons in a shared pair.

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4
Q

What does an Ionic Bond consist of?

A

An electrostatic force between cations (+ve) and anions (-ve).

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5
Q

What does a Covalent Bond consist of?

A

An electrostatic force between two nuclei (+ve) and the shared electron pair (-ve).

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6
Q

What does a Dative Covalent Bond consist of?

A

An electrostatic force between two nuclei and the shared electron pair.

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7
Q

Describe the strength of an Ionic Bond, Covalent Bond and Dative Covalent Bond.

A
  • Ionic Bond: Strong
  • Covalent Bond: Strong
  • Dative Covalent Bond: Strong, indistinguishable from normal covalent bond once formed
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8
Q

Describe the polarity of an Ionic Bond, Covalent Bond and Dative Covalent Bond.

A
  • Ionic Bond: Polar Bond (A+ - B-)
  • Covalent Bond: Non-Polar / Polarised (A - B / A+ - B-)
  • Dative Covalent Bond: Often Polar (A+ - B-)
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9
Q

Describe the states of an Ionic Bond, Covalent Bond and Dative Covalent Bond.

A
  • Ionic Bond: Solid at RTP
  • Covalent Bond: Gases / Liquids / Solids at RTP
  • Dative Covalent Bond: Gases / Liquids / Solids at RTP
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10
Q

Describe the solubility of an Ionic Bond, Covalent Bond and Dative Covalent Bond.

A
  • Ionic Bond: Soluble in water
  • Covalent Bond: Depends on the molecule
  • Dative Covalent Bond: Depends on the molecule (often reacts with water)
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11
Q

What is Metallic Bonding?

A

The electrostatic attraction between metal ions and mobile, delocalised electrons.

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12
Q

Define Delocalised.

A

Not associated with a particular atom.

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13
Q

Describe the forces between different constituents of atoms / ions.

A
  • Repulsive forces between electrons
  • Repulsive forces between positive ions
  • Attractive forces between electrons and positive ions
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14
Q

Describe the requirements of metallic bonding.

A
  • Metal should have low ionisation energies (Metals readily give up their electrons to form positive metal ions)
  • Metal should have vacant valence orbitals (Electrons move freely between the overlapping orbitals)
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15
Q

Describe the characteristics of metals.

A
  • Great strength
  • Good conductors of heat and electricity in solid and liquid states
  • Malleable
  • Ductile
  • Lustrous
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16
Q

What does the strength of a metal depend on?

A
  • Number of electrons

- How closely packed the cations are

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17
Q

Define Intramolecular Forces.

A

Forces that hold atoms together within a molecule.

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18
Q

Define Intermolecular Forces.

A

Forces that hold atoms together between molecules.

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19
Q

Describe the relative strength of Intramolecular Forces and Intermolecular Forces.

A

Intermolecular Forces are much weaker than Intramolecular Forces.

20
Q

State the types of Intermolecular Forces in order of strongest to weakest.

A
  • Ion-Dipole Forces
  • Hydrogen Bonds
  • Dipole-Dipole Forces
  • Dispersion Forces (Van der Waals Forces / London Forces)
21
Q

When do attractive and repulsive forces operate?

A

Between electrons and protons when atoms / molecules approach each other.

22
Q

What is there attraction between?

A

Attraction between permanent charges (ions), permanent dipoles or induced dipoles.

23
Q

How does an instantaneous (temporary) dipole come about?

A

Electrons constantly move in orbitals - at any given moment, there may be more electrons on one side of the atom / molecule than the other.

This dipole induces another dipole in the neighbouring atoms / molecules.

24
Q

What type of force is the attraction between dipoles?

A

A weak intermolecular force (sometimes called Van der Waal’s bonding).

25
When does the strength of London Dispersion Forces increase?
With the number of electrons (size) of a molecule.
26
Describe the significance of London Dispersion Forces.
- Present in all molecules, important in non-polar ones - Boiling points of noble gases, halogens and alkanes - Hardness of certain solids - Behaviour of gases at low temperature - Stabilising lipid bilayers (cell membranes) - Protein structure - Protein-protein recognition
27
What is a Dipole-Dipole Interaction?
An electrostatic attraction between permanent dipoles.
28
Where are Dipole-Dipole Interactions (permanent molecular dipoles) found?
In bonds with an electronegativity difference.
29
What do molecular dipoles require?
A non-uniform charge distribution in 3D.
30
Dipole-dipole attractions act in addition to __________________.
Dipole-dipole attractions act in addition to London Dispersion Forces (Van der Waal) interactions.
31
What do Dipole-Dipole Interactions result in?
Higher boiling points than expected from the mass of the molecule.
32
Describe the significance of Dipole-Dipole Interactions.
- Carbonyls | - Protein folding
33
What is an Ion-Dipole Force?
An electrostatic attraction between an ion and an uncharged polar molecule.
34
What does the strength of Ion-Dipole Forces depend on?
Strength depends on the charge on an ion and the magnitude of the dipole.
35
What are Ion-Dipole Forces most common in?
In solution e.g. KCl dissolving in water
36
What is a Hydrogen Bond?
A primarily electrostatic force of attraction between a hydrogen atom which is covalently bound to a more electronegative atom or group.
37
What is the strongest dipole-dipole interaction?
Hydrogen bonding
38
Describe the requirements of hydrogen bonding.
Acceptor: - An electronegative atom (O, N, F or 𝛿-) - Small size - High charge density - Lone pair of electrons in small orbitals Donor: - A 𝛿+ hydrogen atom in a polar bond (usually N-H, O-H, F-H)
39
Describe the properties of hydrogen bonds.
- Weak and easily broken compared to covalent bonds - Directional - Additive
40
Discuss the significance of hydrogen bonding.
- Large numbers of hydrogen bonds account for the physical state of water - Strong enough for the stability of macromolecules - DNA double helix - Base pairing - Protein secondary structure (alpha helices, beta sheets) - Enzyme-substrate interactions - Antibody-antigen interactions - Solubility of compounds in water
41
State the order of the boiling points of hydrides of different groups (Mr above 100) from highest to lowest.
- Group 6 - Group 5 - Group 7 - Group 4
42
State the order of the boiling points of hydrides (Mr below 50) from highest to lowest.
- H2O - HF - NH3
43
Describe the structure of water.
- Each oxygen atom has 2 lone pairs | - Each water molecule has 2 hydrogen atoms (extensive network of hydrogen bonds)
44
Describe the structure of ice.
- Each water molecule is hydrogen-bonded to 4 others (tetrahedral) in a diamond-like structure - Molecules are further apart in ice than in liquid water = ice is less dense than water
45
Describe the nature of hydrogen bonds in water and ice.
- Ice: Fixed arrangement of H-bonds. | - Water: Disorganised, H-bonds break and reform constantly
46
Describe the significance of Hydrogen Bonding in biology.
- Matching number of hydrogen bond donors and acceptors allow 'correct' pairing of DNA bases - Found in alpha helices and beta sheets where the strongest interactions are between amides, N-H and C=O
47
Describe the bonding in cellulose.
- Major component of plant cell walls - Polymer of glucose - Sugar chains held rigidly together by multiple hydrogen bonds within and between chains - Flat sheets of hydrogen-bonded chains are held together by London Dispersion (VdW) Forces

CLS3003-B: Chemistry (Semester 1) (13 decks)

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