L9 - Chemical Bonding (3) Flashcards
Define Dative Covalent Bond (Co-ordinate Bond).
A covalent bond in which one atom supplies both of the shared electrons in the bond.
What are co-ordinate bonds found in?
- Transition metal complex ions
- Ammonium ion (and other nitrogen-containing complexes)
- Hydroxonium ion
- Carbon monoxide
- Nitric acid
What is a donor?
The atom that supplies the shared pair of electrons.
What is an acceptor?
The atom with a vacant orbital that accepts the electron pair donated by the donor.
What must the atom acting as the donor have?
A lone pair of electrons.
Define Lone Pair.
A pair of electrons in the valence shell of the atom that are not involved in bonding.
Define Complex Ion.
Ions with a central metal ion bonded to one or more molecules / ions.
How does an ammonium ion form?
When ammonia reacts with H+.
How does a complex ion form?
When a transition metal ion dissolves in water.
Provide an example of a complex ion.
Al3+ bonded to 6 water molecules.
What makes transition metals, and elements in periods 1-3 available for bonding?
Transition metals and elements in periods 1-3 have valence electrons in d-orbitals that make them available for bonding.
What does the function of some biological molecules depend on?
Function of some biological molecules depends on binding a metal-ion containing cofactor.
State 8 biological molecules whose function depends on binding a metal-ion containing cofactor.
- Porphyrins
- Corrins
- Haemoglobin
- Myoglobin
- Cytochromes P450
- Vitamin B12
- Chlorophyll
- Photodynamic Therapy
What does the function of some drugs depend on?
Their ability to:
- Act as donors in dative covalent bonds (e.g. chelation therapy)
- Act as acceptors for biological donors
What is D-penicillin amine used for?
Treatment of copper and arsenic poisoning
What is Dimercaprol used for?
Treatment of mercury, lead and arsenic poisoning
What is Desferoxamine used for?
Treatment of iron overdose
What is Cis-platin used for?
Anti-cancer agent
Describe features of drugs which make use of dative covalent bonding.
- Contain a large number of dative covalent bond donors (e.g. oxygen, nitrogen, sulphur)
- Form multiple bonds from one drug molecule to a transition metal ion / a heavy metal ion
- Water soluble groups encourage complexes to be excreted from the body
What does the Valence Shell Electron Pair Repulsion (VSEPR) theory predict?
The structure of simply covalently bonded molecules and ions with:
- One central atom
- Surrounding atoms that are all approximately the same size
What does the 3D shape of a simple molecule / ion achieve?
Keeps repulsive forces to a minimum (electron pairs stay as far apart as possible)
How can the shape of a molecule be predicted?
By counting its electron pairs.
State the number of bonds and bond angle of a Linear shape molecule.
- Number of Bonds: 2
- Bond Angle: 180°
State the number of bonds and bond angle of a Trigonal Planar shape molecule.
- Number of Bonds: 3
- Bond Angle: 120°
State the number of bonds and bond angle of a Tetrahedral shape molecule.
- Number of Bonds: 4
- Bond Angle: 109.5°
State the number of bonds and bond angle of a Trigonal Bipyramidal shape molecule.
- Number of Bonds: 5
- Bond Angle: 90° and 120°
State the number of bonds and bond angle of a Octahedral shape molecule.
- Number of Bonds: 6
- Bond Angle: 90°
Describe how the Steric Effect comes about.
The atoms composing molecules occupy some degree of space, and when atoms come too close together there’s a rise in the energy of the molecule due to the atoms being forced to occupy the same physical space.
What effects does the Steric Effect have?
- Distorts bond angles
- If the surrounding groups on the central atom are not all approx. the same size
State the order of repulsion.
Bond Pair - Bond Pair < Lone Pair - Bond Pair < Lone Pair - Lone Pair
What does a lone pair cause?
Bond angle decreases by approx. 2° per lone pair.
Describe the number of bonds, number of lone pairs and molecular geometry of molecules with the Trigonal Planar domain geometry.
1) Molecular Geometry: Bent Linear
Number of Bonds: 2
Number of Lone Pairs: 1
2) Molecular Geometry: Linear
Number of Bonds: 1
Number of Lone Pairs: 2
Describe the number of bonds, number of lone pairs and molecular geometry of molecules with the Tetrahedral domain geometry.
1) Molecular Geometry: Pyramidal
Number of Bonds: 3
Number of Lone Pairs: 1
2) Molecular Geometry: Bent Linear
Number of Bonds: 2
Number of Lone Pairs: 2
3) Molecular Geometry: Linear
Number of Bonds: 1
Number of Lone Pairs: 3
Describe the number of bonds, number of lone pairs and molecular geometry of molecules with the Trigonal Bipyramidal domain geometry.
1) Molecular Geometry: Seesaw
Number of Bonds: 4
Number of Lone Pairs: 1
2) Molecular Geometry: T-shaped
Number of Bonds: 3
Number of Lone Pairs: 2
3) Molecular Geometry: Linear
Number of Bonds: 2
Number of Lone Pairs: 3
Describe the number of bonds, number of lone pairs and molecular geometry of molecules with the Octahedral domain geometry.
1) Molecular Geometry: Square Pyramidal
Number of Bonds: 5
Number of Lone Pairs: 1
2) Molecular Geometry: Square Planar
Number of Bonds: 4
Number of Lone Pairs: 2
3) Molecular Geometry: T-Shaped (theoretical)
Number of Bonds: 3
Number of Lone Pairs: 3
4) Molecular Geometry: Linear
Number of Bonds: 2
Number of Lone Pairs: 4
What is the bond angle and shape of an ammonia molecule?
- Bond Angle: 107°
- Shape: Pyramidal
What is the bond angle and shape of a water molecule?
- Bond Angle: 104.5°
- Shape: Bent-Linear
What is the bond angle and shape of a ClF5 molecule?
- Bond Angle: <90°
- Shape: Square Pyramidal
What is the bond angle and shape of a SF4 molecule?
- Bond Angle:
- Shape: See-Saw
What is the bond angle and shape of a ClF3 molecule?
- Bond Angle:
- Shape: T-Shaped
What is the bond angle and shape of a XeF4 molecule?
- Bond Angle:
- Shape: Square Planar
What do the different lines/wedges on a 3D diagram represent?
- Dashed line / wedge: away from you, into plane of paper
- Solid line / wedge: towards you, out of plane of paper
Describe the steps for predicting the shape of molecules.
Consider the central atom:
1) Find the number of valence electrons (add / remove electrons for ions)
2) Work out the number of bonding pairs and lone pairs by drawing the Lewis structure of the molecule
3) If there are no lone pairs, the molecular geometry is of the 5 basic types
4) If there are lone pairs, the domain/electronic geometry is still of the 5 basic types, but the molecular geometry is different
Define Polar Bond.
A covalent bond between two atoms where the electrons forming the bond are unequally distributed.
Describe the steps for predicting polarity.
1) Are the bonds polar? If not, the molecule will not be polar.
2) If the bonds are polar, determine the shape of the molecule.
3) Do the polar bonds point in the same direction or oppose one another? Opposing dipoles cancel out.
Describe Polar and Non-Polar bonds with reference to dipoles.
- Polar: Net dipole movement
- Non-Polar: No net dipole movement
