Notes on Chemical Bonding


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Chemical notes on bonding
Ionic bonding
- This occurs between metals and non metals
- Fe2+/3+, Cu+/2+, Zn2+, No3-
- Metals loose electrons, non metals gain electrons.
- Ionic compounds conduct electricity when dissolved, but not when solid, they also have high m & b points due to strong giant 3d lattice. They are also soluble in water as they have a charge
- Metal atoms always form positive charged electrons while non metals from negatively charged electrons
Metallic Bonding
- They conduct electricity due to a sea of delocalised electrons
- They have a lattice of positive atoms.
- Transition metals contribute both S and D electrons in the sea of electrons
- The attraction is between the ions and mobile valence electrons and not between the layers, this means they can bend over each other
- The large the number of valence electrons and the smaller the atoms and the stronger the metallic bonding
Covalent bonding
- Between non metals with high electron values
- Can have single, double, or triple bonds
Bond strength
C – C: single bond, longest type of bond (154) however is the easiest to break (346)
C=C: double bond, second longest bond (134) and second hardest to break (598)
C=C: triple bond, smallest bond (121) however is the hardest to break (837)
Predicting the type of bonding
(1) From electronegativity
Electronegativity is the strength of an element/atom to pull electrons towards itself. Metals have a very low electronegativity as they lose electrons in ionic bonding, however non metals have a higher electronegativity as they gain electrons in ionic bonding.


(2) From position in the periodic table
Metal + non metal = ionic bonding
Non metal + non metal = covalent bonding
Simple molecular structure
Molecular covalent bonds have low m & b points because of weak intermolecular forces called Van Der Waals forces. (more on this later)
Giant covalent structures
Diamond and graphite both have these structures but they are very different. They both have a giant lattice with strong covalent bonds, in the case of Diamond it is 3d and very hard to break in any way, however with graphite it is only 2d so can be broken if cracked in a certain way. These structures have very high melting and boiling points.
Buckminsterfullerere
A family of ball shaped C-molecules in which there are around 60 atoms which are found in ball shapes. Uses are being investigated in nano-thecnology. These substances are soluble in non-polar solvents
Polar bonds
The larger the difference in electronegativity the greater the strength of the polar bond.
Now the hard stuff

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Bond angles and shapes of molecules
Number of non-bonding electron pairs Example Lewis diagram Bond angle Shape
No non bonding electrons, four bonded groups around the element Methane
CH4 109.5
Tetrahedral
One free pair of electrons, three bonding pairs Ammonia
NH3 107
Trigonal
Pyramidal
Two free pairs of electrons, two pairs of electrons bonding Water
H2O 104
Non-linear

Five bonded pairs of electrons around the centeral element without any non bonded electrons
Phosphorus pentafluoride
PF5
90 & 120
Trigonal bipyramidal
Four bonded pairs of electrons with one pair of non bonding electrons around the central element Sulfur Tetrafluoride
SF4 90 & 117
Saw horse
Three bonding pairs of electrons with two non bonding pairs of electrons Iodine Trichloride
ICl3 90
T-shaped
Two bonding pairs of electrson with three non bonding pairs of electrons Xenon Difluoride
XeF2 180
Linear

Hybridisation
Sigma bonds are when one of the following happen,
- S and S bonds overlap
- S and P bonds over lap
- P and P bonds overlap
Pie bonds happen when,
- A p and p orbital sandwich an S orbital
Pie bonds sigma bonds

There are three types of hybridisation, these are,
- When there are only two orbital’s and the shape is linear (180) this makes it Sp hybridization
- When there are three orbital’s and the shape is Trigonal planer (107) this makes it sp2 hybridization
- Where there are four orbital’s and the shape is tetrahedral (109.5) this makes it Sp3


Intermolecular forces
- Van der waals forces affect everything
- The random movement of electrons can cuase an instantaneous diapole or a temporary diapole, this induces a force of attraction called van der waals forces.
- The bigger the molecules and the larger the contact area the bigger the force
- Van der waals forces are the weakest intermolecular forces, but in very large molecules there can be an effect on b & m points

- Dipole-dipole intermolecular forces occur with molecules with a permanent difference of electronegativity.
- In liquids the moving molecules sometimes attract and sometimes repel but the net effect is always attraction
- These forces are stronger than Van Der Waals forces


- Hydrogen bonding can only occur between Hydrogen and Nitrogen/oxygen/fluorine (NOF)
- it is the strongest of the weak bonds.
- It has a profound effect on m & b points.
- H2O has for higher melting and boiling points then it should do because it is the optimum molecule for Hydrogen bonding.


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