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Chemistry Semester 1 > L9 Covalent bonding II > Flashcards

L9 Covalent bonding II Flashcards

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1
Q

What is a dative (or co-ordinate) covalent bond?

A

= bond formed by sharing two e- when both the e- are provided by one of the linked atoms (or ions)
Co-ordinate bond: found in transition metal complex ions
* Behaves the same as a normal covalent bond

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2
Q

What is a donor atom?

A

= The atom that supplies the shared pair of e- in a dative covalent bond.

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3
Q

What is an acceptor atom?

A

= The atom that doesn’t contribute any e- to the shared pair of e- in a dative covalent bond.

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4
Q

What is required for dative covalent bond formation?

A

The atom acting as the donor must have a lone pair of e- in its valence shell AND the atom acting as the acceptor should have a vacant bonding orbital.

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5
Q

What is a steric factor?

A

= the maximum number of ligands that can bond to a transition metal ion - can form up to six dative covalent bonds (because water molecules is small).

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6
Q

Give examples of dative covalent bonding and its role in biology?

A
  • The function of some biological molecules depends on binding a metal ion-containing cofactor - porphyrins, corrins
  • In biological systems water is the most common ligand
    Examples:
  • Haemoglobin - 4 haem group
  • Myoglobin - 1 haem group
  • Cytochromes P450
  • Vitamin B12 - contains Fe, Co
  • Chlorophyll - contains Mg
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7
Q

How does carbon monoxide poisoning work?

A

CO, NO2 have a higher affinity for the haemoglobin than oxygen, blocking the carrying of oxygen
-> the CO-haemoglobin complex is bright red = someone with CO poisoning looks flushed

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8
Q

What is dative covalent bonding’s function in medicine?

A

Function of some drugs depends on their ability to act as donors or acceptors in biological dative covalent bonds

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9
Q

How does D-penicillinamine bond?

- what does it treat?

A

Contains a large no. of dative covalent bond donors (O, N, S) so it can form multiple bonds to a single heavy/transition metal ion.
Treats: Copper & arsenic poisoning because it has water soluble roots which encourage the molecule to be excreted from the body

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10
Q

How does Dimercaprol bond?

- what does it treat?

A

Contains a large no. of dative covalent bond donors (O, N, S) so it can form multiple bonds to a single heavy/transition metal ion.
Treats: Mercury, lead & arsenic poisoning because it has water soluble roots which encourage the molecule to be excreted from the body

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11
Q

How does Desferoxamine bond?

- what does it treat?

A

Contains a large no. of dative covalent bond donors (O, N, S) so it can form multiple bonds to a single heavy/transition metal ion.
- It can form six bonds around iron
Treats: Iron overdoses because it has water soluble roots which encourage the molecule to be excreted from the body
* patients urine looks like rose wine when they excrete it.

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12
Q

How does Cis-Platin bond?

- what does it treat?

A

Forms a dative covalent bond with a metal ion
Treats: cancer
- In the body it hydrolyses -> the nitrogen ligands get swapped with water
- In the tumour the water molecules get swapped for nitrogen atoms in DNA -> causes cross linking & a toxic affect on cell division.

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13
Q

How are the shapes of molecules predicted?

A

= Valence Shell Electron Pair Repulsion theory (VSEPR)
- the 3D shape of a simple molecule/ion is that which keeps repulsiove forces to a minimum - e- pairs stay as far away from each other as possible

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14
Q

2 bp molecule

A

= Linear

  • 180 degrees
  • e.g. BeCl2
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15
Q

3 bp molecule

A

= Trigonal planar

  • 120 degrees
  • e.g. AlCl3
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16
Q

4 bp molecule

A

= Tetrahedral

  • 109.5 degrees
  • e.g. CH4
17
Q

5 bp molecule

A

= Trigonal bipyramid

  • 90 & 120 degrees
  • e.g. PCl5
18
Q

6 bp molecule

A

= Octahedral

  • 90 degrees
  • e.g. SF6
19
Q

2 bp, 1 lp molecule

A

Domain geometry = Trigonal planar

Molecular geometry = Bent linear

20
Q

1 bp, 2 lp molecule

A

Domain geometry = Trigonal planar

Molecular geometry = Linear

21
Q

3 bp, 1 lp molecule

A

Domain geometry = Tetrahedral

Molecular geometry = Pyramidal

22
Q

2 bp, 2 lp molecule

A

Domain geometry = Tetrahedral

Molecular geometry = Bent linear

23
Q

1 bp, 3 lp molecule

A

Domain geometry = Tetrahedral

Molecular geometry = Linear

24
Q

4 bp, 1 lp molecule

A

Domain geometry = Trigonal bipyramid

Molecular geometry = Seesaw

25
Q

3 bp, 2 lp molecule

A

Domain geometry = Trigonal bipyramid

Molecular geometry = T-shaped

26
Q

2 bp, 3 lp molecule

A

Domain geometry = Trigonal bipyramid

Molecular geometry = Linear

27
Q

5 bp, 1 lp molecule

A

Domain geometry = Octahedral

Molecular geometry = Square pyramidal

28
Q

4 bp, 2 lp molecule

A

Domain geometry = Octahedral

Molecular geometry = Square planar

29
Q

3 bp, 3 lp molecule

A

Domain geometry = Octahedral
Molecular geometry = T-shaped
* Theoretical - has never been synthesised

30
Q

2 bp, 4 lp molecule

A

Domain geometry = Octahedral

Molecular geometry = Linear

31
Q

How do lone pairs affect bond angles?

A

They distort the bond angle decreasing it by approximately 2 degrees per lp.

32
Q

How do bonding repulsion strengths differ?

A

bp-bp < lp-bp < lp-lp

33
Q

What is domain geometry?

A

= the molecular structure that exists when there are only bp, no lp

34
Q

What is molecular geometry?

A

= the actual molecular structure that exists including lp

35
Q

How do you predict polarity?

A
  1. Are the bonds polar - a polar molecule needs polar bonds
  2. Determine the shape of the molecule
  3. Do the polar bonds point in opposite directions? Opposite dipoles cancel
    e. g. water is polar, carbon dioxide isn’t
36
Q

What is a dipole?

A

= e- being pulled in one direction (toward the electronegative atom) in the bond

Chemistry Semester 1 (12 decks)

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