A 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 by one.
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.
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
NaAl
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
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:
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
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
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
Metallic character of the elements
Elements on the left are metallic...right are non-metals...Si
is a metalloid.
Acidic character of the oxides
Metal oxides are basic
Aluminium oxide is amphoteric (reacts with both acids and bases)
Home
Al
steady increase
HCl + HClO
