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

L10 - Chemical Bonding (4) Flashcards

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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
Q

When does the strength of London Dispersion Forces increase?

A

With the number of electrons (size) of a molecule.

26
Q

Describe the significance of London Dispersion Forces.

A
  • 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
Q

What is a Dipole-Dipole Interaction?

A

An electrostatic attraction between permanent dipoles.

28
Q

Where are Dipole-Dipole Interactions (permanent molecular dipoles) found?

A

In bonds with an electronegativity difference.

29
Q

What do molecular dipoles require?

A

A non-uniform charge distribution in 3D.

30
Q

Dipole-dipole attractions act in addition to __________________.

A

Dipole-dipole attractions act in addition to London Dispersion Forces (Van der Waal) interactions.

31
Q

What do Dipole-Dipole Interactions result in?

A

Higher boiling points than expected from the mass of the molecule.

32
Q

Describe the significance of Dipole-Dipole Interactions.

A
  • Carbonyls

- Protein folding

33
Q

What is an Ion-Dipole Force?

A

An electrostatic attraction between an ion and an uncharged polar molecule.

34
Q

What does the strength of Ion-Dipole Forces depend on?

A

Strength depends on the charge on an ion and the magnitude of the dipole.

35
Q

What are Ion-Dipole Forces most common in?

A

In solution

e.g. KCl dissolving in water

36
Q

What is a Hydrogen Bond?

A

A primarily electrostatic force of attraction between a hydrogen atom which is covalently bound to a more electronegative atom or group.

37
Q

What is the strongest dipole-dipole interaction?

A

Hydrogen bonding

38
Q

Describe the requirements of hydrogen bonding.

A

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
Q

Describe the properties of hydrogen bonds.

A
  • Weak and easily broken compared to covalent bonds
  • Directional
  • Additive
40
Q

Discuss the significance of hydrogen bonding.

A
  • 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
Q

State the order of the boiling points of hydrides of different groups (Mr above 100) from highest to lowest.

A
  • Group 6
  • Group 5
  • Group 7
  • Group 4
42
Q

State the order of the boiling points of hydrides (Mr below 50) from highest to lowest.

A
  • H2O
  • HF
  • NH3
43
Q

Describe the structure of water.

A
  • Each oxygen atom has 2 lone pairs

- Each water molecule has 2 hydrogen atoms (extensive network of hydrogen bonds)

44
Q

Describe the structure of ice.

A
  • 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
Q

Describe the nature of hydrogen bonds in water and ice.

A
  • Ice: Fixed arrangement of H-bonds.

- Water: Disorganised, H-bonds break and reform constantly

46
Q

Describe the significance of Hydrogen Bonding in biology.

A
  • 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
Q

Describe the bonding in cellulose.

A
  • 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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