Periodicity (sl)
3.1 - The Periodic
Table
Brief description
An list of the chemical elements arranged into Groups (the
columns going down) and Periods (the rows going across)
The group number gives the number of valence (outer shell)
electrons around the atom.
The period number is the same as that of the outer energy
shell.
Elements increase in atomic number across each period, and
down each group.
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Example
Calcium is in the 2nd group therefore it has 2 electrons
in the outer shell and a valency of +II. It is in the fourth period
therefore its outer electrons are in the fourth energy shell.
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Trends
in physical properties 
3.2 - Physical
Properties
| Characteristic |
Trend (left to right) |
Reason |
| Atomic radius |
decreases in size from left to right |
increased attractive force (acting on the same energy
shell) of the nucleus increases as the number of protons increases |
| Ionic radius |
decreases across the period until formation
of the negative ions then there is a sudden increase followed by a
steady decrease to the end |
In general as above. The sudden increase
on formation of negative ions is due to the new (larger) outer shell |
| Electronegativity |
Increases |
More electron attracting power of the larger
nuclear charge as we move to the right |
| Metallic character |
Decreases - Na, Mg, Al metals; Si metalloid;
P, S, Cl, Ar non-metals |
Metallic character is a measure of the ease
of loss of electrons from the outer shell. This decreases with increasing
nuclear charge. |
| Melting point |
Na Al
steady increase |
Increasing availability of electrons in the metallic
bonding associated with greater charge density of the metal
ion |
| Si massive increase |
Si giant macromolecular structure |
| P large decrease |
P4 molecules |
| S small increase |
S8 molecules |
| Cl
Ar decrease |
Cl2 molecules and Ar atoms |
|
The elements of group 1
| Characteristic |
Trend (descending group 1) |
Reason |
| Atomic radius |
increases in size top to bottom |
The number of electron shells increases from
Li to Cs |
| Ionic radius |
increases from Li to Cs |
The number of electron shells increases from
Li to Cs |
| Electronegativity |
decreases |
Attracting power of the nucleus is sheilded
by the inner electron shells increasingly as the group is descended |
| Ionisation energy |
Decreases descending the group |
Sheilding effect of the inner electron shells
increases as we descend the group and so the outer electron is more
easily removed |
| Melting point |
| Decreases from Li to Cs |
The larger ions have weaker metallic bonding as
their charge density (charge/volume ratio)is smaller |
|
The elements of group 7 (Fluorine to Iodine)
| Characteristic |
Trend (descending group 7) |
Reason |
| Atomic radius |
increases in size from F to I |
The number of electron shells increases from
F to I |
| Ionic radius |
increases from F to I |
The number of electron shells increases from
F to I |
| Electronegativity |
decreases |
Attracting power of the nucleus is sheilded
by the inner electron shells increasingly as the group is descended |
| Ionisation energy |
Decreases descending the group |
Sheilding effect (repusion caused by the
inner electrons) of the inner electron shells increases as we descend
the group and so the outer electron is more easily removed |
| Melting point |
| Increases from F to I |
The larger halogens have greater Van der Waals
forces holding the molecules together as they have more electrons
|
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3.3 Chemical Properties
Reactions of elements of the same group are similar because
they have identical outer shells (ie same number of valence electrons).
The following must be covered:
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Reactions of group 1(alkali metals) and group 7 (halogens)
elements with water
-
Reaction of group 1 (alkali metals) elements with group
7 (halogens)
-
Displacement reaction of halogens
-
Reaction of silver ions with halide ions (group 7 element
ion)
-
Acidity/basicity of the element oxides
- The metallic /non-metallic nature of the elements
Reactions of group 1 and 7
| Element |
reagent |
example equation |
conditions (if any) |
| Group 1(Li...Cs) |
water |
2Na + 2H2O --> 2NaOH + H2 |
violent reaction |
| Group 1(Li...Cs) |
halogen |
2Na + Cl2 --> 2NaCl |
heat needed |
| |
|
|
|
| Group 7 (halogen) |
water |
Cl2 + H2O 
HCl + HClO |
|
| |
|
|
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Displacement reaction of halogens
Reactivity of the halogens decreases going down the
group and the more reactive halogen will displace a less reactive
halogen from a solution of its ions. This is also a redox reaction.
|
|
Cl-(aq)
|
Br-(aq)
|
I-(aq)
|
| Cl2 |
Colorless / no reaction
|
turns red due to formation of bromine
|
turns brown due to formation of iodine
|
| Br2 |
no reaction
|
no reaction
|
turns brown due to formation of iodine
|
| I2 |
no reaction
|
no reaction
|
no reaction
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The reactions of Halide ions with Silver ions
|
|
Cl-(aq)
|
Br-(aq)
|
I-(aq)
|
| Ag+ |
white ppt
|
cream ppt
|
yellow ppt
|
| reason |
insoluble AgCl formed
|
insoluble AgBr formed
|
insoluble AgI formed
|
| equation |
Ag+ + Cl- AgCl
|
Ag+ + Br- AgCl
|
Ag+ + I- AgI
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Metallic character of the elements
Elements on the left are metallic...right are non-metals...Si
is a metalloid.
Acidic character of the oxides
-
-
Aluminium oxide is amphoteric (reacts with both acids and bases)
-
Non-metal oxides are acidic
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