PowerPoint PresentationWhat is Inorganic Chemistry?
Inorganic chemistry is the chemistry of all the elements – organic
refers to a few at the top right-hand part of the periodic
To understand inorganic chemistry properly we need to be aware of
aspects of physical chemistry, analytical and even organic
Because Inorganic comprises all the elements, we need some way to
understand the underlying connections and to figure out why things
work the way they do.
Fortunately, the nature of the elements themselves provides us with
such a guide and we can understand a lot from the arrangement of
the periodic table itself.
Mendele’ev 1869-1871 made first modern periodic table
Tables before based on alchemy, or “ideal” numbers (triads or
Mendele’ev arranged elements by increasing mass and similar
properties (density and reactivity) but had no underlying
One of the biggest successes of this table was the prediction of
unknown elements (Sc, Ga, Ge)
Amazingly, it wasn’t until more than 40yrs later (with the quantum
interpretation of atomic structure) that people would understand
the structure of the periodic table.
In any event, the rationale he used (elements connected by similar
chemistry) ended up being useful.
The group structure of the periodic table is still useful.
If one wants to differentiate between the groups of the periodic
table. Much reactivity can be understood in this manner, which is
the reason for the typical arrangement of the table (although the
colours are a nice touch)
Group names alkaline metals, alkaline earth metals, earth metals,
nothing, pnictogens, chalcogens, halogens, noble gases, transition
metals, lanthanides and actinides
Oddities in older tables are left over from Mendele’ev derived
tables e.g. A and B designations, order of B groups
Another common scheme differentiates by the physical properties of
the elements. In this case, metals are colourless, semi-metals are
green, non-metals are yellow and the noble gases are blue.
This explains the diagonal line that we often see on the periodic
More importantly, this view of the periodic talble shows us that
there seems to be an obvious organization of the properties of
non-metals (top right), semi-metals, and metals (everything
Such views of the table seem to indicate that there is an
underlying reason why something is metallic or not and we will see
that this is truly the case later.
Other properties that are much more important for an understanding
of the chemistry of seemingly unrelated elements are sometimes best
depicted in other ways.
We will see later that electronegativity is one of the most
important concepts that allows us to understand inorganic
You may also notice that, in regard to the last slide that we saw,
the trends of electronegativities seem to match the trends in
metallic and non-metallic character.
We will see later that there is a reason for this correspondence,
although electronegativity is a theoretical construct (not a
fundamental measurable property).
WebElements is a good site to take a look at.
This alternative version of a periodic table emphasizes the
electronic configuration of the elements and the symmetrical nature
of the periodic table.
E.g. Arsenic, one of the elements that I worked with a lot during
It is not as effective in showing the chemical relationship group
nature, which is one reason why it’s not generally used.
In this course we will focus on the chemistry of the Main Group
elements, which are those of the s- and p-blocks. These are the
elements of groups 1 and 2 and groups 13-18, respectively and
contain most of the elements that we encounter on an everyday
Furthermore, an understanding of the structure, bonding and
reactivity of these elements provides the necessary foundation for
the understanding of how things work at the molecular level.
One of the unfortunate things about this table is the green band
calling periods 2 and 3 “typical elements” – the opposite is
actually true, but these include the elements of organic chemistry
and have been studied the most.
Because the periodic table will be our guide throughout this
course, I want you to be able to identify all the elements up to Kr
(#36). What I mean by this is that I will give you a blank periodic
table at the start of each midterm and you should be able to fill
in those elements. I don’t usually want people to memorize
anything, but this is important.
Complex (polyatomic ions) Na2(SO4)
Network Solids diamond, graphite (C) “red” phosphorus (P)
Network ions Mg3(Si2O5)(OH)2 (talc)
Network Solids SiO2, polymers
Solid/Liquid Metals Hg, Ga, Na, Fe, Mg
Because Inorganic chemistry includes everything in the periodic
table, there are an incredible number of different types and forms
of compound that we want to understand.
Elements (and their various allotropes)
Although the meaning of elements is clear, the division between
ionic and covalent is more arbitrary – as we shall see in the next
Covalent = sharing
Ionic = stealing
All of the subdivisions I have listed here are sort of arbitrary as
well and are different than those that you will find in different
Molecular Solids P4, S8, C60
Network Solids diamond, graphite (C) “red” phosphorus (P)
Solid/Liquid Metals Hg, Ga, Fe, Na, Mg
No drawing for atomic and molecular gases
Molecular species all at the top right of periodic table
Allotropes of C, and Phosphorus include both molecular and network
structures (network just implies infinite arrangement of covalently
Although metals may look similar to network solids, in the “body
center cubic” structure of iron depicted at bottom right, those are
not the same kind of bond as is the covalent network
Properties of metals can vary a lot from liquid mercury and almost
gallium, to soft sodium, to hard tungsten – we will get into the
reasons for this later.
Network ions Mg3(Si4O10)(OH)2 (talc)
Ionic compounds range from the familiar binary salts (which are
usually very hard) that are arranged in various types of
essentially infinite lattices. E.g. the sodium chloride structure
that we are all familiar with.
The ones I have termed complex, contain complex ions such as
nitrate, sulfate, phosphate, tetrachloroaluminate etc. And
properties depend on the nature of the cations and anions and how
they pack together.
Ionic compounds containing network ions are also quite common,
especially for minerals. As in the case of the elements, the
arrangement of the network has a large effect on the properties of
the material. Talc is constructed from linked units of (Si4O10)
fragments – the polyhedra, which makes layers. Some layers are held
together by the cations but others are not – this allows layers to
slide, so talc is not a hard material like salt.
Complex Molecular As(C6H5)3, organometallic compounds
Network Solids SiO2, polymers
The covalent compounds of inorganic chemistry are much more
interesting than those of organic chemistry – one of the reasons
that I decided to study inorganic chemistry in the first
For the most part, covalent organic structures are all based on
tetrahedral, planar, or linear arrangements of atoms.
Water, ammonia and carbon dioxide are typical of organic–type
bonding, but even simple inorganic structure can have many more
interesting structures like the trigonal bipyramid of PF5.
The polyatomic and organometallic type compounds can have
incredible structures. E.g. boranes and carboranes have cluster
structures like the icosahedral one shown here – I solved the two
structures shown in the middle using X-ray crystallography.
There are also many network-type compounds such as quartz and many
One thing you may notice is that the structures can vary
drastically depending on the element (CO2 vs SiO2) – we will find
out why this is as the course progresses.
Entropy Change, DS°
Enthalpy is “heat content” of a substance
Standard Enthalpy of Formation, DH°f
DH° for the formation of a substance from its constituent
Standard Enthalpy of Fusion, DH°fus Na(s) Na(l)
Standard Enthalpy of Vapourization, DH°vap Br2(l) Br2(g)
Standard Enthalpy of Sublimation, DH°sub P4(s) P4(g)
Standard Enthalpy of Dissociation, DH°d ½ Cl2(g) Cl(g)
Standard Enthalpy of Solvation, DH°sol Na+(g) Na+(aq)
Enthalpies of formation can be found in books such as text books
and CRC handbook.
These ones include phase changes and dissociation of molecules into
atoms, which will be important for calculations we will do
Na(g) Na+(g) + e- DH°ie = 502 kJ/mol
Al(g) Al+(g) + e- DH°ie = 578 kJ/mol
Al+(g) Al2+(g) + e- DH°ie = 1817 kJ/mol
Al2+(g) Al3+(g) + e- DH°ie = 2745 kJ/mol
Al(g) Al3+(g) + e- DH°ie = 5140 kJ/mol
Ionization enthalpies are always positive – it requires energy to
rip an electron away from a nucleus.
More later on the magnitudes
The enthalpy change for the gain of an electron
Cl(g) + e- Cl-(g) DH°ea = -349 kJ/mol
O(g) + e- O-(g) DH°ea = -142 kJ/mol
O-(g) + e- O2-(g) DH°ea = 844 kJ/mol
Electron Affinity, EA = -DH°ea + 5/2 RT
EA = -DH°ea
Electron Affinity is the negative of the electron attachment
They will provide us information about the strength of
bonding in solids.
Average O-H bond energy = 918 / 2
EO-H = 459 kJ/mol
DH = 1724 kJ/mol
EN-H = 391 kJ/mol
We can estimate N-N bond energy to be:
1724 – 4(391) = 160 kJ/mol
DHrxn = (436 + 745) – (414 + 351+ 464) kJ/mol
DHrxn = -48 kJ/mol
For H2N-NH2(g): EN-N = 160 kJ/mol
For F2N-NF2(g): EN-N = 88 kJ/mol
For O2N-NO2(g): EN-N = 57 kJ/mol
They are only a rough approximation and predictions must be
At STP: DG° = DH° - (298.15 K) DS°
The two factors that determine
if a reaction is favourable:
If it gives off energy (exothermic)
DH = SHproducts - SHreactants
DS = SSproducts - SSreactants
DG lets us predict where an equilibrium will lie through
DG = -RT ln K
So if DG < 0, then K > 1 and equilibrium lies to the
There are three possible ways that this can happen with
respect to DH and DS.
aA + bB + cC + … hH + iI + jJ + …
i.e. DH < 0 and DS > 0 then DG < 0.
S(s) + O2(g) SO2(g) DH° = -292.9 kJ/mol
TDS° = 7.5 kJ/mol
DG° = -300.4 kJ/mol
If enthalpy drives the reaction:
i.e. DH < 0 and DS < 0, but |DH| > |TDS|, then DG <
N2(g) + 3 H2(g) 2 NH3(g) DH° = -46.2 kJ/mol
TDS° = -29.5 kJ/mol
DG° = -16.7 kJ/mol
If entropy drives the reaction:
i.e. DH > 0 and DS > 0, but |DH| < |TDS|, then DG <
NaCl(s) Na+(aq) + Cl-(aq) DH° = 1.9 kJ/mol
TDS° = 4.6 kJ/mol
DG° = -2.7 kJ/mol
Measure change in equilibrium constants with temperature
to get DH° using the relationship:
Measure the equilibrium constant for the equilibrium,
then determine DG° using the relationship ? :
DG° = -RT ln K
Often not that easy…
gives access to DG° through the following relationship:
DG° = - nF DE°
F = Faraday’s constant = 96.4867 kJ mol-1 V-1 (e-)-1
Note: if DG° < 0, then must be DE° > 0
So favourable reactions must have DE° > 0
This is more important for Analytical chemistry, but we might talk
more about redox reactions later.
Sn4+(aq) + 2 e- Sn2+(aq) DE° = 0.15 V
2 Al(s) + 3 Sn4+(aq) 2 Al3+(aq) + 3 Sn2+(aq)
DE° = -(-1.67 V) + (0.15 V) = 1.82 V for 6 electrons
So: DG° = - nF DE° = - (6 e-)F (1.82 V) = -1054 kJ/mol
Standard is H+ e- -> ½ H2
Relative Energy vs. Oxidation State (under certain
What is the energy of electron gain
What is the energy of electron loss
Some important information provided by Frost diagrams:
Oxidation state diagrams (Frost Diagrams)
The most useful aspect of Frost diagrams is that they allow us to
predict whether a RedOx reaction will occur for a given pair of
reagents and what the outcome of the reaction will be. This is
described in the handout.