INORGANIC
Part 5 Period 5 survey, group trends page
sub-index: 5.1
Period 3 survey of individual elements
: 11. sodium :
12. Magnesium
:
13. Aluminium :
14. Silicon :
15. Phosphorus :
16. Sulfur
:
17. Chlorine :
18. Argon *
5.2 Period 3 element trends
& explanations of physical properties * 5.3
Period 3 element trends in bonding, structure, oxidation
state, formulae & reactions
Advanced
Level Inorganic Chemistry Periodic Table Index *
Part 1
Periodic Table history
* Part 2
Electron configurations, spectroscopy,
hydrogen spectrum,
ionisation energies *
Part 3
Period 1 survey H to He *
Part 4
Period 2 survey Li to Ne * Part
5 Period 3 survey Na to Ar *
Part 6
Period 4 survey K to Kr and important trends
down a group *
Part 7
s-block Groups 1/2 Alkali Metals/Alkaline Earth Metals *
Part 8
p-block Groups 3/13 to 0/18 *
Part 9
Group 7/17 The Halogens *
Part 10
3d block elements & Transition Metal Series
*
Part 11
Group & Series data & periodicity plots * All
11 Parts have
their own sub-indexes near the top of the pages
5. Survey
of Period
3: Na across to Ar (8 elements, Z = 11 to 18)
5.3 Period 3 trends in bonding, structure, oxidation
state, formulae & reactions
M+
X- ionic bond, Mδ+-Xδ+
polar bond and M-X a relatively
non-polar bond (no partial charges shown)
Element |
Sodium |
Magnesium |
Aluminium |
Silicon |
Phosphorus |
Sulfur |
Chlorine |
Argon |
old/latest Group |
1 |
2 |
3/13 |
4/14 |
5/15 |
6/16 |
7/17 |
0/18 |
ZSymbol
|
11Na |
12Mg |
13Al |
14Si |
15P |
16S |
17Cl |
18Ar |
Structure of element |
solid metallic
lattice of Na+ and free e- |
solid metallic
lattice of Mg2+ and free e-s |
solid metallic
lattice of Al3+ and free e-s |
solid giant
covalent lattice Sin |
solid small
covalent molecules P4 |
solid small
covalent molecules S8 |
gaseous small
covalent molecules Cl2 |
gaseous single atoms Ar |
electron configuration |
[Ne]3s1 |
[Ne]3s2 |
[Ne]3s23p1 |
[Ne]3s23p2 |
[Ne]3s23p3 |
[Ne]3s23p4 |
[Ne]3s23p5 |
[Ne]3s23p6 |
common oxidation states
e.g. in oxides,
chlorides, hydrides |
+1
max +1 |
+2
max +2 |
+3
max +3 |
+4
max +4 |
+3, +5
max +5 |
-2, -2, +4, +6
max +6 |
-1, +1, +3,
+5, +7
max +7 |
at Xe can get max of +8 in some compounds,
but not for Ar! |
electronegativity of element |
0.93 |
1.31 |
1.61 |
1.90 |
2.19 |
2.58 |
3.16 |
3.20 |
formula of oxides
(oxidation states of the period 3 element) |
Na2O,
Na2O2 (+1) |
MgO (+2) |
Al2O3
(+3) |
SiO2
(+4) |
P4O6 and
P4O10 (+3,
+6) |
SO2,
SO3 (+4, +6) |
Cl2O, ClO2,
Cl2O7
(+1,+4,+7) |
- |
Ratio of
period 3 element to oxygen (formulae in bold) |
1 : 0.5 |
1 : 1 |
1 : 1.5 |
1 : 2 |
1 : 2.5 |
1 : 2.5 |
- |
- |
bonding
and structure of oxides |
ionic lattice |
ionic lattice |
ionic lattice |
solid covalent giant
structure |
solid covalent small
molecules |
covalent small
gaseous
molecules |
covalent small
gas/liquid
molecules |
- |
Melting
point of oxide in highest oxidation state |
1275oC |
2852oC |
2072oC |
1723oC |
580oC |
17/62oC |
-91oC |
- |
electronegativity difference X-O (O
is 3.44) nature of bond |
2.51 ionic
Na+ O2-or
O22- |
2.13 ionic
Mg2+ O2- |
1.83 ionic with
some covalent character
Al3+ O2- |
1.54 covalent
Siδ+-Oδ- |
1.25 covalent
Pδ+-Oδ- |
0.86 covalent
Sδ+-Oδ- |
0.28 covalent
Clδ+-Oδ- |
- |
formula of chlorides |
NaCl |
MgCl2 |
AlCl3 |
SiCl4 |
PCl3,
PCl5 |
S2Cl2,
SCl2, SCl4 |
Cl2 |
- |
bonding in chlorides |
ionic lattice |
ionic lattice |
ionic lattice, readily vaporises to covalent dimer molecules Al2Cl6 |
covalent small
liquid
molecules |
liquid covalent small
molecules |
covalent small
liquid
molecules |
small
diatomic gaseous molecule |
- |
electronegativity difference X-Cl
(Cl is 3.16) nature of bond |
2.23
Na+ H- |
1.85
Mg2+ Cl- |
1.55
Al3+ Cl- |
1.26
Siδ+-Clδ- |
1.25
Pδ+-Clδ- |
0.58
Sδ+-Clδ- |
0.00
Cl-Cl |
- |
Formula of hydride |
NaH |
MgH2 |
AlH3 |
SiH4 |
PH3 |
H2S |
HCl |
- |
bonding and structure of hydride |
ionic lattice |
'polymer-like' structure of
intermediate ionic/covalent nature |
'polymer-like' structure of
intermediate ionic/covalent nature |
small covalent gaseous molecule |
small covalent gaseous molecule |
small covalent gaseous molecule |
small covalent gaseous molecule |
- |
electronegativity difference X-H (H is 2.20) nature of bond |
1.27
Na+ H- |
0.89
Mgδ+-Hδ- |
0.59
Alδ+-Hδ- |
0.30
Si-H |
0.01
P-H |
0.38
Hδ+-Sδ- |
0.96
Hδ+-Clδ- |
- |
-
TOP OF PAGE
-
The
structure and physical properties of the elements
(see also section 5.1)
-
The trend is metal
lattice ==> giant covalent structure ==> small covalent
molecules
-
Sodium Na, magnesium Mg and
aluminium Al
are silvery solids, with a metal lattice structure, high boiling
points and are good
conductors of heat/electricity due to the delocalised free
electrons moving between the immobile metal ions.
-
Si has a
non-metallic giant covalent structure based on a tetrahedral
arrangement of S-Si bonds and is a poor conductor of
heat/electricity.
-
Phosphorus P4,
sulfur S8 and chlorine Cl2 are simple-small covalent
molecules and Ar consists of single atoms. The molecules are
only held together by the weakest of the intermolecular forces,
namely the instantaneous dipole - induced dipole forces, and
consequently have very low melting/boiling points.
-
-
-
Electron
configuration and oxidation states
-
Electron configurations
of 2,8,1 or 1s22s22p63s1
to 2,8,8 or 1s22s22p63s23p6
-
Filling
the s orbital (max 2 e-'s) gives the metallic s-block
elements of Groups 1-2,
-
filling the p orbitals gives the
predominantly non-metallic p block elements of Group 3-7, 0
(Gps 13-18) bar aluminium for Period 3.
-
Oxidation states
in compounds (numerically = valency) are: sodium Na (+1 only),
magnesium Mg (+2
only), aluminium Al (+3 only), Si (+4, -4 with electropositive metals), P (usually -3, +3 or +5), S
(-2, +4 and +4), Cl (-1, +1, +3, +5 and +7), Ar has no stable
compounds due to the full outer quantum level (shell) being
full, conferring extra electronic stability on the atom.
-
-
-
Reaction of
element with oxygen and the structure of the oxide (see
also section 5.1)
(Gp 1) 4Na(s)
+ O2(g) ==> 2Na2O(s)
and Na2O2
on heating the metal in air |
(Gp 2) 2Mg(s)
+ O2(g) ==> 2MgO(s)
on heating metal in air |
(Gp 3)
4Al(s)
+ 3O2(g) ==> 2Al2O3(s)
needs high temperature |
(Gp 4)
Si(s) + O2(g)
==> SiO2(g)
needs high temperature |
(Gp 5)
P4(s)
+ 5O2(g) ==> P4O10(s)
on heating in air |
(Gp 6)
S(s)
+ O2(g) ==> SO2(g)
and a little SO3
on heating in air |
(Gp 7) Chlorine -
no reaction |
(Gp 0) Argon - no
reaction |
(Gp 1) Na2O(s)
+ H2O(l) ==> 2NaOH(aq)
pH 13-14
strong base from ionic oxide
ionic equation:
(Na+)2O(s)
+ H2O(l) ==> 2Na+(aq) + 2OH-(aq)
or Na2O2(s)
+ 2H2O(l) ==> 2NaOH(aq)
+ H2O2(aq) |
(Gp 2) MgO(s)
+ H2O(l) ==>
Mg(OH)2(aq/s)
~pH 11-12 weak base from ionic oxide
ionic equation:
Mg2+(s) + H2O(l)
==> Mg2+(aq) + 2OH-(aq) |
(Gp 3)
Al2O3,
insoluble, no reaction with water (pH remains at 7), but amphoteric with
respect to strong acids and strong bases (alkalis) |
(Gp 4) SiO2,
insoluble, no reaction with water (pH remains at 7), but weakly acidic and
will dissolve a little in strong bases (alkalis) e.g. conc. NaOH(aq) |
(Gp 5)
P4O6(s) +
6H2O(l) ==> 4H3PO3(aq)
~pH 2 weak
acid from covalent oxide
P4O10(s) +
6H2O(l) ==> 4H3PO4(aq)
pH
0-1
strong acid from covalent oxide
Because phosphoric(V) acid is tribasic,
there are three possible 'phosphate' anions
H2PO4-,
HPO42- and PO43- |
(Gp 6) SO2(aq)
+ H2O(l) ===> H2SO3(aq)
sulfurous acid, theoretically dibasic, but the main ionic
reaction is
SO2(aq)
+ H2O(l)
H+(aq) + HSO3-(aq)
pH 2-3
weak acid from covalent oxide
There are two possible anions
HSO3-
hydrogensulfite or hydrogensulfate(IV) ion
and SO32-
sulfite or sulfate(IV) ion
SO3(g)
+ H2O(l) ==> H2SO4(aq)
pH 0-1
strong acid from covalent oxide
Sulfuric(VI) is dibasic so there are two
possible anions HSO4-
hydrogensulfate or hydrogensulfate(VI) ion
SO42- sulfate or
sulfate(VI) ion |
(Gp 7)
Cl2O(g)
+ H2O(l) ==> 2HClO(aq)
~pH 3?
weak acid from covalent oxide
Cl2O7(l)
+ H2O(l) ==> 2HClO4(aq)
pH 1
strong acid from covalent oxide |
(Gp 0) argon has no
oxide |
-
The chemical character of the
oxides - reaction of the Period 3 oxides with water, acids or
alkalis.
-
Relating bonding character to
acid - base character of the oxide.
-
The ionically bonded oxides of
sodium and magnesium form bases - alkaline solutions in water.
-
The large difference in
electronegativity (see table) allows the ionic bond and hence the
oxide ion to exist.
-
The oxide ion is a strong
Bronsted-Lowry base i.e. a strong attractor of protons and the oxide
ion abstracts a proton from a water molecule to give the hydroxide
ion, hence an alkaline solution is formed.
-
O2-(s) + H2O(l)
==> 2OH-(aq)
-
Aluminium oxide, ionic with some
covalent character, is amphoteric.
-
The covalent oxides of the
non-metals, Si, P, S and Cl, all form acids (weak or strong).
-
So the trend in oxide character
across period 3 is from strongly basic oxides of metals to strongly
acidic oxides of non-metals.
-
Sodium oxide/peroxide Na2O/Na2O2
and magnesium oxide MgO are basic and form an alkali in water
(see above) and salts with acids (examples below).
-
Na2O(s) + 2HCl(aq)
==> 2NaCl(aq) + H2O(l)
-
Na2O(s) + H2SO4(aq)
==> Na2SO4(aq) + H2O(l)
-
MgO(s) + 2HCl(aq) ==>
MgCl2(aq) + H2O(l)
-
MgO(s) + 2HNO3(aq) ==>
Mg(NO3)2(aq) + H2O(l)
-
See
reactions of acids for
lots more examples with sulfuric acid and nitric acid too with
oxides and hydroxides.
-
The equations with phosphoric(V)
acid are the trickiest to balance and the examples below assume
total neutralisation of the tribasic phosphoric(V) acid!
-
3Na2O(s) + 2H3PO4(aq)
==> 2Na3PO4(aq) + 3H2O(l)
-
3MgO(s) + 2H3PO4(aq)
==> Mg3(PO4)2(aq) + 3H2O(l)
-
Aluminium oxide Al2O3
has no reaction with water, insoluble, but is amphoteric and forms salts with
(i) acids and
(ii) alkalis.
-
Silicon(IV) oxide
(silicon dioxide) SiO2 has no
reaction but is weakly acidic forming salts with alkalis.
-
Phosphorus(III) oxide P4O6
and phosphorus(V) oxide P4O10 are moderately-strong acidic oxides
forming phosphoric(III) acid H3PO3 and
phosphoric(V) acid H3PO4 on reaction with
water.
-
Therefore the oxides are acidic
and form salts with bases.
-
You can formally write an
equation for dissolving phosphorus(V) oxide in sodium hydroxide to
form trisodium phosphate(V), but its not as simple as this!
-
Generally speaking, in a
series of oxides for the same element, the higher the oxidation state of X in a 'XxOy'
series, the more acidic is the oxide, so H3PO4
is a stronger acid than H3PO3.
-
The oxides or acids are
readily neutralised to give phosphate salts e.g.
-
H3PO4
(aq) + NaOH(aq) ==> NaH2PO4(aq) + H2O(l)
-
Two further reactions
are possible with the sodium hydroxide to give
Na2HPO4
and Na3PO4.
-
Sulphur dioxide will
dissolve in alkalis to form sulfate(IV) salts (sulfites) e.g.
-
SO2(g) + 2NaOH(aq) ==>
Na2SO3(aq) + H2O(l)
-
Although weakly acidic, it will
displace weaker acidic oxides e.g.
-
SO2(g) + CaCO3(s)
==> CaSO3(s) + CO2(g)
-
This reaction forms part of the
chemistry of desulfurization of flue gases from fossil fuel power
station furnaces.
-
Sulfur in fossil fuels burns to
form sulfur dioxide - a major air pollutant.
-
The flue gases are 'scrubbed'
mixing them with air and passing the gas mixture through a slurry of
wet limestone powder to form harmless calcium sulfate (which can be
used as the commercial product gypsum).
-
SO2(g) + CaCO3(s)
+ 0.5O2(g) ==> CaSO4(aq/s) + CO2(g)
-
The gypsum is formed as calcium
sulfate dihydrate CaSO4.2H2O(s)
-
Chlorine(I) oxide Cl2O and
chlorine(VII) oxide Cl2O7 are
moderate to strong acidic in water.
-
The overall patterns,
from left to right across Period 3 is ...
-
giant ionic lattice ==>
giant covalent lattice ==> small covalent molecules
-
In terms of overall chemical
character ...
-
This is chemically characteristic of
metallic ==> non-metallic
element character.
-
-
-
TOP OF PAGE
-
Reaction of element
with chlorine and the structure of the chloride
(see also section 5.1)
(Gp 1)
2Na(s)
+ Cl2(g) ==> 2NaCl(s) |
(Gp 2)
Mg(s)
+ Cl2(g) ==> MgCl2(s) |
(Gp 3)
2Al(s) + 3Cl2(g) ==> 2AlCl3(s)
|
(Gp 4)
Si(s)
+ 2Cl2(g) ==> SiCl4(l) |
(Gp 5)
P4(s)
+ 3Cl2(g) ==> 4PCl3(l)
P4(s)
+ 5Cl2(g) ==> 4PCl5(s) |
(Gp 6)
2S(s)
+ Cl2(g) ==> S2Cl2(l) also
unstable SiCl2, SiCl4 |
(Gp 7)
chlorine itself |
(Gp 0) no reaction with argon |
(Gp 1)
NaCl(s)
+ aq ==> Na+(aq) + Cl-(aq)
just
dissolves, ~pH 7 |
(Gp 2) MgCl2(s)
+ aq ==> Mg2+(aq) + 2Cl-(aq)
just
dissolves, ~pH 7 |
(Gp 3)
AlCl3(s)
+ 3H2O(l) ==> Al(OH)3(s)
+ 3HCl(g)
with limited
water you get hydrolysis to give acid fumes
AlCl3(s)
+ aq ==> Al3+(aq) + 3Cl-(aq)
excess
water, weakly acidic solution due to the acidity of [Al(H2O)6]3+ |
(Gp 4)
SiCl4(l)
+ 2H2O(l) ==> SiO2(s) + 4HCl(aq)
hydrolysis
to give strongly acid solution |
(Gp 5)
PCl3(l)
+ 3H2O(l) ==> H3PO3(aq)
+ 3HCl(aq)
hydrolysis
to give weakly acid solution
PCl5(s)
+ 4H2O(l) ==> H3PO4(aq)
+ 5HCl(aq)
hydrolysis to give strongly acid solution |
(Gp 6) S2Cl2(g)
+ H2O(l) ==> HCl(aq), S(s),
SO2(aq), H2SO3(aq), H2SO4(aq),
H2S(aq)
complex
redox - hydrolysis reaction but final solution is quite acidic
|
(Gp 7)
chlorine itself |
Gp 0
argon has no chloride |
(Gp 1)
2Na(s) + 2H2O(l) ==>
2NaOH(aq) + H2(g) |
(Gp 2)
Mg(s)
+ 2H2O(l) ==> Mg(OH)2(aq)
+ H2(g) |
(Gp 3)
aluminium has no reaction with water |
(Gp 4)
silicon has no reaction with water |
(Gp 5)
phosphorus has no reaction with water |
(Gp 6)
sulfur has no reaction with water |
(Gp 7)
Cl2(g) + H2O(l)
HClO(aq) + HCl(aq) |
(Gp 0) argon has no reaction with water |
See also
4.1 Period 2 Survey of the
individual elements, 4.2 Period
2 element trends and explanations of physical properties * 4.3 Period 2 element trends in bonding,
structure, oxidation state, formulae & reactions,
5.1
Period 3 survey of individual elements, 5.2 Period 3 element trends
& explanations of physical properties, 6.1
Survey of
Period 4 elements, 6.2 Period 4 element trends in physical properties, 6.3
Period 4 element trends in bonding, formulae and
oxidation state and
6.4
Important element trends down a Group
A level Revision notes for GCE Advanced
Subsidiary Level AS Advanced Level A2 IB
Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters
Chemistry CIE Chemistry, WJEC GCE AS A2 Chemistry, CCEA/CEA GCE AS A2 Chemistry revising courses for pre-university students
(equal to US grade 11 and grade 12 and AP Honours/honors level courses)
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