OCR F334 The Materials Revolution

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F334 Chemistry of Materials: The Materials Revolution
Bonding and Structure
(a) explain the term electronegativity; recall qualitatively the electronegativity trends in the Periodic Table; use
relative electronegativity values to predict bond polarity in a covalent bond;
Electronegativity is a measure of the ability of an atom in a molecule to attract electrons in a chemical bond to
itself.
To decide the polarity of a covalent bond, we need a measure of each atom's attraction for bonding electrons it's
'electron pulling power '. This is called electronegativity atoms with strong electron pulling power to covalent
bonds are said to be highly electronegative .
We can use differences in electronegativity to predict how polar a particular covalent bond will be. For example,
in the CF bond, F has a higher electronegativity value (4.0) than C (2.6) so it attracts the shared electrons more
strongly and the polarity of the bond is:
If atoms have similar electronegativities , they are nonpolar . For example, C has an electronegativity value of 2.6
and H has an electronegavity value of 2.2.
decide whether a molecule is polar or nonpolar from its shape and polarity of its bonds;
Polar Molecules Nonpolar Molecules
explain, give examples of and recognise in given example the following types of intermolecular bonds:
Instantaneous Electron movements in a molecule causes an uneven distribution of charge, forming an
dipole induced instantaneous dipole. The instantaneous dipole gets close to a neighbouring molecule ,
inducing a dipole in that molecule and becomes attracted to it.
dipole Straight chains chains pack more closely and there is a larger molecular surface
area so harder to break.
Long chain length a larger molecular surface area so more IDID, which is
harder to break.
These intermolecular forces are the weakest .

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F334 Chemistry of Materials: The Materials Revolution
Permanent The + and charges on polar molecules cause weak electrostatic forces of attraction
dipole ­ between molecules, e.g. HCl (H is + and chlorine is ).
These intermolecular forces are stronger than instantaneous dipole induced dipole.
permanent
dipole
Hydrogen Bonds Hydrogen bonding is the strongest type of intermolecular bond.…read more

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F334 Chemistry of Materials: The Materials Revolution
In general, the longer the chains then the stronger the polymer:
longer chains are more tangled together difficult for the chains to slide over each other , so reducing
flexibility.
longer chains have more points of contact with chains of neighbouring polymer molecules more
intermolecular bonds , which means that the chains are attracted to each other more strongly . Therefore, it
is more difficult for the chains to slide over each other less flexible.…read more

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F334 Chemistry of Materials: The Materials Revolution
(i) describe the hydrolysis of esters and amides by both aqueous acids and alkalis, including salt formation
where appropriate
Step 1: Break the weakest bond :
Step 2: Add H2O
OH adds to C=O
H adds to N
Step 3:
Change the structure of the product depending on H+ (acid) or OH (Alkali)
Amide :
o Acid add hydrogen to NH 3 =
ammonia
o Alkali remove hydrogen on
carboxylic acid to make O
Ester:
o Acid no…read more

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F334 Chemistry of Materials: The Materials Revolution
Acylation to An acyl group is added to form an amide .
form an Ammonia reacts with an acyl chloride to form a primary amide. In this example, ethanamide
is formed.
amide
A primary amide reacts
with an acyl chloride to
form a secondary
amide.…read more

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F334 Chemistry of Materials: The Materials Revolution
Complex ions containing ammonia ligands have their counterparts in
amine chemistry. For example, adding butyl amine to aqueous copper(II) sulfate produces a
2+
dark blue complex ion, [Cu(C 4H
9NH 2)
4(H
2O) 2]
, with a similar structure to the compound
stated above.
As The lone pair of electrons on the nitrogen atom in ammonia attacks electrophiles , such as
nucleophiles the positively polarised carbon atoms in halogenoalkanes .…read more

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