AQA Chemistry, Unit 1, Periodicity

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Elements are classified as s, p or d block according to which orbitals the high energy electrons are in.
This can also be deciphered from an element's position in the periodic table:
Trends across period 3
Atomic Radius:
General Decrease
Increased nuclear charge, but electrons are being
added to the outer shell, meaning shielding is the
same. So increased nuclear charge cause the
atoms to constrict
First Ionisation Energy
General Increase
No change in shielding, higher atomic charge and
smaller atomic radius make it harder to remove
outer electron.
Drop at Al, as outer electron is in higher energy 3p
subshell for the first time.
Drop at S as electron is paired for the first time
within the 3p subshell.

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Melting and Boiling Points
Dependent on structure and bonding.
Na, Mg and Al ­ Giant metallic structures,
therefore strong attraction between metal ions
and delocalised electrons. Stronger Na <Mg < Al
due to stronger attraction between ions with a
higher charge and more delocalised electrons her
Si ­ Giant Covalent structure (Tetrahedral),
therefore strong covalent bonds between every atom must be broken.
P, S, Cl & Ar ­ Molecular, therefore low mp and bp.…read more


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