Chemistry AQA AS Unit 1 Periodicity

Made these notes for my year 12 summer exam to revise and read over. There are spelling mistakes in most of my files but due to the busy exam schedule I had no time to correct them (sorry).

Most files have more information than what is needed but I feel it helps you feel more confident walking into the exam if you have a greater knowledge background and may help when having to apply knowledge to questions. Good luck :)

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  • Created by: Chelcie
  • Created on: 02-09-13 13:10
Preview of Chemistry AQA AS Unit 1 Periodicity

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Periodicity
Period 3
Group 1, 2, 3 (Na, Mg, Al) are metals. Giant structures. They lose their out electrons to form ionic
compounds.
Silicon has 4 electrons in its outer shell hence forming 4 covalent bonds. Semi metal.
Groups 5, 6, 7 (Ph, Su, Cl) are non-metals. They either accept electrons to form ionic compounds or
share to form covalent.
Giant structures (found on left of periodic table) tent to have high melting/boiling points.
Molecular/atomic structures (found on right) tend to have low melting/boiling points.
The melting points increase from sodium to aluminium
because of the strength of the metallic bonding as
more electrons join the sea of delocalised electrons
that hold the giant metallic lattice together.
The melting points of the non-metals with molecular
structures depend on the V.D.W forces. As a result:
S> P> Cl
Silicon with its giant structure has a much higher
melting point.
Atomic Radii
Atoms get larger as we go down the group as there is greater shielding due to an increase of
energy levels going down the group. Therefore the outer electron main level is further from the
nucleus so the atomic radii increases.
Atoms decrease across a period because the number of protons increase as the electrons in the
outer shell increase, with no further shielding effects. This increased charge pulls in electrons and
hence the size of the atom decreases.
First Ionisation Energy
Decreases down a group as the number of filled energy inner levels increase. This provides greater
shielding with the outer electrons being further away from the nucleus as a result. Less energy is
therefore needed to remove an outer electron.
Increases across a period as the number of protons in the nuclei increases and as the electrons
enter the same main level there is no change in shielding effects. Therefore the increased charge on
the nucleus means it get increasingly difficult to remove an electron.
Drop in ionisation energy from one period to the next because going down periods we start a
new main level, so there is an increase in atomic radius, the outer electron is further from the nucleus,
less strongly attracted to the nucleus and hence easier to remove.

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The drop in first ionisation energy between groups 2 and 3 (Mg, Al)
This is because the electron in the aluminium p sub shell is already in a higher energy level than the
s-electron in magnesium, so it takes less energy to remove it.…read more

Page 3

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This shows that the higher the electrons are on the graph, the closer the electrons are to the nucleus.…read more

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