Everything Covalent

revision notes for OCR chemistry A spec for covalent bonding, shapes of molecules, intermolecular forces and electronegativity 

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  • Created on: 13-11-11 20:45
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Everything covalent
In a covalent bond an electron occupies the space between the two atoms nuclei its
Negative electrons are attracted to positive nucleus, overcomes repulsion
between two positive nucleus.
Covalent bonds are directional.
Lone pairs > outer shell electron pair not involved in chemical bonding only the central atom
Gives a concentrated region of negative charge around the atom.
Influence the chemistry of the molecule eg the shape of the molecule.
Dative covalent bonds ­ shared pair of electrons which has been provided by ONE of the
bonding atoms only.
Covalent bond being chemically bonded to an ion eg ammonium ion NH4+ =
NH3+ H+ the H+ ion has no electrons so nitrogen proves both from its lone
pair. Having an extra costume for Halloween and sharing.
Shape of molecules
Pairs include double and triple bonds
2 pairs ­ 180º - linear e.g. co2
3 pairs - 120º - Trigonal planar e.g. BF3
4 pairs ­ 109.5º - Tetrahedral e.g. CH4
6 pairs - 90º - octrahedral
Molecules containing lone pairs
Subtract 2.5 from expected bond angle for each lone pair
4 pairs ­ including 1 lone pair 107 pyramidal e.g. NH3
4 pairs ­ including 2 lone pairs 104.5 non linear e.g. H2O
Lone pairs repel bond pairs more than bond pairs repel each other.
Electro negativity
A measure of the attraction of a bonded atom to the shared pair of electrons in a covalent
Electro negativity increases along and up the periodic table making Fluorine the most
electro negative element followed by oxygen chlorine nitrogen
Increases left to right because;
Nuclear charge increases
Electrons are in the same shell
Increases top to bottom
Electrons are closer to and less shielded from the nucleus
Outweighs a smaller nuclear charge.
Measured on a scale of 0 4 (Pauling scale)
Predicting bonding type

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Small difference in electro negativity; PH3
Contains almost pure covalent bonds
3.0 2.2
4 0
ii. Larger difference in covalent bonds; NH3
N is more electro negative than H
Na Cl
0.9 3.1
3 6
iii.…read more

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Ice is less dense than water because when frozen the water
molecules spread apart to form an open lattice in order to
maximise the number of hydrogen bonds.
iii. Van de Waals' forces
In a molecule electrons are constantly moving
At any one time the electrons may become unevenly distributed which
forms a temporary dipole.
This will induce temporary dipoles in neighbouring molecules, which then
attract.…read more


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