Periodicity
HL and SL
3.1 The periodic table
The periodic table is a list of all the elements in order of
increasing atomic number.
Elements are placed vertically in GROUPS according to the
number of electrons in their outer energy level. These groups are
numbered 1 – 7 and 0.
All the elements in the same group have similar chemical
properties as they have the same number of electrons in their
outer energy level.
The number of electrons in the outer energy level is the same as
the group number.
There is a gap between groups 2 and 3 for the TRANSITION
ELEMENTS.
The elements are arranged horizontally in PERIODS.
The periods are number 1 – 7 and the period number indicates
the number of energy levels containing electrons.
H and He are in period 1 so have 1 energy level containing
electrons.
Li to Ne are in period 2 so have 2 energy levels containing
electrons etc.
You should be able to locate an element in the periodic table
from its electron arrangement alone.
On a blank copy of the Periodic Table indicate the position of
the elements A to J (not their actual symbols).
A: 2
B: 2, 1
C: 2, 8, 2
D: 2, 8, 5
E: 2, 6
F: 2, 3
G: 2, 8
H: 2, 8, 8, 1
I: 2, 8, 7
J: 2, 8, 4
3.2 Physical Properties
Important definitions:
FIRST IONISATION ENERGY – Energy required to remove
one electron from an atom of an element to form a gaseous ion
with a 1+ charge.
ELECTRONEGATIVITY – The ability of an atom to pull
electron density from a covalent bond to itself.
Now try the ‘Physical Properties’ exercise.
3.3 Chemical Properties
• Elements of group 1 with water and with chlorine
• Halogens with halide ions (halogen displacements)
• Oxides of period 3
Watch the video clip and use it to write down information on
group 1 elements.
For fun:
Rubidium and
caesium
Brainiac style
The video clip shows the
reaction of sodium with
chlorine gas to make sodium
chloride as a white
crystalline solid.
2Na(s) + Cl2(g)  2NaCl(s)
The other members of the group react in a similar fashion to form
white crystalline chlorides. The vigour of the reaction again
increases down the group. Lithium burns in chlorine with a red
flame and potassium with a lilac flame.
Explain the reactivity trend using Bohr’s model of the atom.
Watch the video clip and use it to write down information on
group 7 elements.
Key idea: a more
reactive halogen
displaces a less
reactive halogen from
one of its compounds.
Reactions of Period 3 Elements
The solid elements (Na to S) all burn in air or oxygen when
ignited.
Video clips over the next few slides show some of the reactions.
Sodium with oxygen
Sodium burns with a
yellow flame forming
the oxide.
2Na(s) + ½O2(g)  Na2O(s)
Magnesium to Phosphorus with
Oxygen
Magnesium, aluminium,
silicon and phosphorus burn
when ignited, emitting a very
bright white light and white
smoke of the oxides. The
reactions are all exothermic.
This clip shows magnesium and oxygen
Mg(s) + ½O2(g)  MgO(s)
2Al(s) + 1½O2(g)  Al2O3(s)
Si(s) + O2(g)  SiO2(s)
P4(s) + 5O2(g)  P4O10(s)
Sulphur with oxygen
Sulphur burns with a blue
flame, but much less
vigorously than the
previous elements, to form
the pungent, colourless gas
sulphur dioxide.
S(s) + O2(g)  SO2(g)
Tabulate the melting points of the oxides of sodium to sulphur
and use these values to deduce the structure and bonding of
these oxides.
Tm / K
bonding
structure
Na2O
1548
ionic
lattice
MgO
3125
ionic
lattice
Al2O3
2345
lattice
SiO2
1883
ioniccovalent
covalent
P4O10
573
covalent
molecular
SO2
200
covalent
molecular
macromolecular
Reactions of oxides of group 3
with water:
sodium
Sodium oxide dissolves to form a
strongly alkaline solution.
Na2O(s) + H2O(l)  2NaOH(aq)
magnesium
Magnesium oxide is also soluble in
water. It dissolves to form a weakly
alkaline solution of magnesium
hydroxide.
MgO(s) + H2O(l)  Mg(OH)2(aq)
aluminium
Aluminium oxide is insoluble in
water.
However, aluminium oxide is
described as AMPHOTERIC as it
will react with both acids and bases.
silicon
Silicon dioxide is insoluble in
water.
However, silicon dioxide is
considered to be an acidic oxide.
phosphorus
Phosphorus(V) oxide dissolves
readily in water to form a weakly
acidic solution.
P4O10(s) + 6H2O(l)  4H3PO4(aq)
sulphur
Sulphur dioxide dissolves in water
to form a solution of sulphurous
acid (a weak acid).
SO2(g) + H2O(l)  H2SO3(aq)
Sulphur trioxide dissolves in water
to form a solution of sulphuric acid
(a strong acid).
SO3(g) + H2O(l)  H2SO4(aq)
The highest oxide of chlorine (Cl2O7) also dissolves in water to
from an acidic oxide.
Complete the table below:
Formula Na2O
of oxide
Structure
and
bonding
Ionic
lattice
Nature of Strong
alkali
oxide