Revision notes on periodicity. From UCL alumni on the trends that occur across a period. These notes on unit 3.2.1 is tailored to the AQA specification for paper 1 Alevel chemistry.
They also include everything that the examiners will be examining you on int he examination.
AQA- periodicity
Allery chemistry revision notes
An element is classified as s, p, d, or f block according to its position in the
periodic table which is determined by its proton number.
The trend in atomic radius, first ionisation energy and melting point of the
element Na-Ar. The reason for these trends in terms of the structure of and
bonding in the elements.
Student should be able to:
-explain the trends in atomic radius and first ionisation energy
-explain the melting point of the melting point of the elements in terms
of their structure and bonding.
Element in the same group (columns) have the same number of electrons in the
outer shell. The group number relates to the number of electrons in the outer
shell. Eg group 2 elements have 2 electrons in their outer shell.
Elements in the same period(rows) have the same number of electron shells. As
you go across period 3 the atomic radius decreases, there is an increased
nuclear charge as there is an increasing number of proton.
Elements in the same group have similar properties. Eg group 1 elements react
with water within releasing vigour as you go down the group.
Atomic radius
This pulls the outer shell of electron further in towards the nucleus. Crucial the
extra electron element grain across the period go into the same shell. The
shielding effect is similar.
Atomic radius increases down the group due to extra electron shells added for
each element down the group.
Melting point
First 3 elements in period three are metal. They have metallic bonding. General
increase in melting point as melting ions have an increasing positive charge,
increasing number of delocalised electrons and smaller ionic radius. This means
a stronger metallic bond.
Silicon has the highest melting point in period three. It has a giant covalent
(macromolecular) structure. Many strong covalent bonds hold the silicon atoms
together. Large amounts of energy is needed to overcome these strong covalent
bonds.
Phosphorous has the formula P4 . It has a lower melting point than silicon due to
a weaker simple molecular structure. Melting point is determined by weaker van
der waals forces. Sulphur has a formulary of S8 . It has a higher melting than
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