Bonding and Structure Flashcards
Ionic Bond Definiton
Strong electrostatic forces of attraction between oppositely charged ions
Physical Properties of Ionic Compounds
High Melting/Boiling Points
- They have a giant ionic lattice structure
- There are many strong electrostatic forces of attraction between oppositely charged ions
Factors affecting the strength of ionic bonds
Greater ion charge = Stronger Ionic Bond
Smalle ionic radius = Stronger Ionic Bond
Smaller = More attractive
Electrical Conductivity
Ionic Compounds WILL NOT conduct electricity in the SOLID state as ions are in a fixed lattice position which means no mobile charged carriers (ions,atoms etc)
They WILL conduct electricity in the molten/aqueous state as the ions are free to move
Solubility
Ionic compounds WILL dissolve in water as the ions make attractions to the different atoms in water and are ‘pulled apart’
Covalent Bond (2 non metals) Definition
A covalent bond is a shared pair of electrons between atoms
Coordinate/dative covalent bonding
When one atom provides both the electrons needed to form a covalent bond
- Atom donating needs to have a lone pair
- Atom receiving needs to have a vacant orbital
- Bond represented with an arrow
Molecular geometry
2bprs, 0lprs - 180° - Linear
3bprs, 0lprs - 120° - Trigonal Planar
4bprs, 0lprs - 109.5° - Tetrahedral
3bprs, 1lpr - 107° - Trigonal Pyramid
2bprs, 2lprs - 104.5° - Non-Linear
6bprs, 0lprs - 90° - Octahedral
Repulsion
LP-LP repulsion>BP-LP repulsion>BP-BP
each lone pair reduces the bond angle by 2.5°
Electronegativity Defintion
The ability of an atom to attract a pair of electrons in a covalent bond
Increased electronegativity
Number of protons increase
Atomic radius decreased
If going up then shielding decreased
Polar Bond
||||| A covalent bond in which there is an unequal share if the electrons due to differing electronegativity |||||
(the electron density is distributed unequally)
If the difference in electronegativity is greater that 0.4 the bond will be polar
Electron density
Delta Negative will be the bigger side
Delta Positive is the smaller side
Opposite sides create a dipole
Symmetry/Polarity
Some molecules have polar bonds but they are not polar molecules because they are symmetrical and the dipoles cancel out
C-H bonds are non polar
Intermolecular Forces
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Covalent bonding leads to the formation of giant or simple molecules
Most Covalent compounds are simple molecules eg water
Intermolecular forces are weaker that the covalent bonds between the atoms within the molecule
3 Intermolecular Forces
Weakest : Induced Dipole-Dipole forces between molecules
Middle : Permanent Dipole-Dipole forces between molecules
Strongest : Hydrogen Bonding between molecules
Temporary Dipole
Electrons constantly moving so the charge can change distribution at any time - one side of a molecule can be more negative than another because the electrons moved closer to that side
Induced Dipole-Dipole/London Forces
(In all simple molecules)
A temporary dipole in one molecule induces a dipole in another molecule
Attraction between delta positive on one molecule and delta negative on an adjacent molecule
This is called induced dipole dipole intermolecular forces
Factors affecting the strength of IDDs
Size/Mr of the molecule - bigger molecule = more electrons = stronger attraction = more IDD forces between molecules
S.A Contact - more S.A contact = more IDD forces between molecules
Larger molecule = Stronger IMFs = higher melting/boiling point
Permanent Dipole-Dipole Forces between polar molecules
- This type of force occurs between molecules which are polar
- A polar bond is where there is a difference in electronegativity between the atoms
- There is an attraction between a delta positive on one molecule and a delta negative on another adjacent molecule
Hydrogen Binding between molecules
Only occurs between polar molecules which have a hydrogen bond directly bonded to O,N or F
O,N,F are the most electronegative atoms
Big difference in electronegativity between negativity between H and the O,N,F
So the O,N,F will pull the pair of electrons in the bond very strongly towards themselves
So the hydrogen nucleus is very delta positive
A lone pair of electrons in a neighbouring molecule containing O,N,F is attracted to the hydrogen
Features of a Hydrogen Bonding Diagram
Hydrogen bond clearly show between the lone pair and the delta positive Hydrogen on the other molecule
Partial Charges in all atoms
All lone pairs shown clearly
The anomalous properties of water
Explaining why water has a relatively high melting/boiling point
Hydrides of Group 4 elements : As the Mr(size) increases, the boiling point increases
Overall trend due to the increasing strength of IDDs
Hydrides of Group 6 elements :
anomaly (H20) which is really high due to the presence of hydrogen bonds
rest increase due to increasing strength of IDDs Hydrides
Physical properties of Simple Molecular structures
Low melting/boiling points
-Weak IMFs between molecules which require little energy to overcome
Electrical Conductivity
WONT conduct electricity in solid/molten state because there are no charged particles free to move (no mobile charged carries)
Solubility
Non-polar molecules WONT generally dissolve in water because they can’t form hydrogen bonds
