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Inorganic Chemistry

A Study Guide

Discussion Questions

Introduction to inorganic chemistry

In this study guide, you will find many questions and some suggestions about answering them. Many questions are open ended. The suggestions focus on certain aspects.

This is a picture of a silicate crystals. Silicate is the most abundant inorganic material. Small grains of silicates are usually called sand.

Define Inorganic Chemistry

Chemistry is the experimental and theoretical study of materials on their properties at both the macroscopic and microscopic levels. Understanding the relationship between properties and structures/bonding is also a hot pursuit. Chemistry is traditionally divided into organic and inorganic chemistry. The former is the study of compounds containing at least one carbon-hydrogen bonds. By default, the chemical study of all other substances is called inorganic chemistry, a less well defined subject.

However, the boundary between organic and inorganic compounds is not always well defined. For example, oxalic acid, H2C2O4, is a compound formed in plants, and it is generally considered an organic acid, but it does not contain any C-H bond.

Inorganic chemistry is also closely related to other disciplines such as materials sciences, physical chemistry, thermodynamics, earth sciences, mineralogy, crystallography, spectroscopy etc.

In this inorganic chemistry, we are planning to cover the following topics, however the plan may change depending on circustances.

Thermal and kinetics in chemical reactions (chemical energetics)
Inorganic macromolecules (Catenation)
The solid states (crystalline solides, defects)
The gaseous states and the atmosphere
Water conditioning
Oxidation and reduction reactions
Electrochemistry and corrosion
Chemistry and agriculture
Sulfur and industrial chemistry
As study guides are made up for these topics, the above titles will be hyperlinked to appropriate documents.

What is a material and how is it related to these terms: matter, mixture, substance, compounds, aggregates, solutions, elements, compounds, composit, etc.?

In general, a material has a mass, and occupies a volume. Such a definition distinquish material from energy, because energy has zero mass and occupies no volume. However, energy causes materials to change, say from solid to vapour or expanding.

In order to make a sense of the material world, we need to be able to classfy materials. A classification can be made according to properties, qualities, structure and bonding, composition, or application. Thus there are many terms used to describe materials.

Inorganic chemistry stresses the composition at the macroscopic level. It is also concerned with the structure and bonding at the atomic and molecular levels. In this view, materials are classified in the following way:

Materials such as silicon carbide, water, and hydrogen chloride (gas), consisting of only one component are called substances or compounds. They are usually made up of two or more chemical elements, which are substances that cannot be decomposed into simpler substances by chemical means. We can organize this classification in the following manner:

           Materials (solid, liquid, gas)
             /               \
  (pure) Substances        = Mixtures =
    /         \           /            \
Elements    Compounds    Homogenerous    Heterogenerous
|           |            mixtures        mixtures
Isotopes    Isomers      |               |            \
                         Solutions       Colloids     Composit

A chunk of material such as a rock containing several kinds of solid is an aggregate. Different kinds of material may bind to each other tightly, and they are also called composit material, ceramics, or blend in engineering. A solution containing two or more types of material may freeze into a homogeneous solid called a solid solution. When the materials are loosely bonded, the chunk may be called a mixture.

At some temperatures, materials exist as liquids which is a fluid. Unlike solids, liquids have no definite shape because the molecules, atoms or ions in the material can slide over each other easily. They take the shape of the container, but they have definite volumes. Two liquids may mix homogeneously or heterogenerously. If boundaries are visible, the two liquids are said to be in separate phases. If the mixture is homogeneous, it is a liquid-liquid solution, or simply solution.

The word matter is sometimes used interchangably with material, but matter often is used to mean particle-like entities such as electrons, protons, rather than wave like electromagnetic radiations or photons.

Carbon exists in the forms of diamond, graphite, and buckminsterfullerene. They have very different properties. We usually consider them different materials, but all are made of the same element carbon. Is it possible to make something harder than diamon? Find it out from this link, which gives a nice view on the exploration of the material world.

What are chemical elements?

Today, you all know that symbols of chemical elements are listed in the Period Table of Elements, and their names ranging from hydrogen to uranium. You probably also know that elements heavier than uranium are man made.

However, you probable do not realize that this question is a fundamental problem asked by philosophers and scientists. Human have asked:

What are materials made of?
How many different basic elements there are in nature?
How do they combine to make so many different substances?
Why do materials undergo changes?
The answers to these questions change over time:

The Chinese Book of Change written during the Chu dynasty (1134-247 BC) suggested two ultimate constituents as Yin (the cosmic female) and Yang (cosmic male). Combination of different proportions of these two fundamental constituents made all the materials and phenomena they experienced in their World.

Plato (427-347 BC) proposed that the material were made up of four primal substances: File, Earth, Water and Air. A less well known fifth one was Ether.

Robert Boyle (1627-1691) experimented with air, and found different kinds of air. He suggested that the existence of some chemical elements that cannot be decomposed into any thing simpler.

Lavoisier (1743-1794) published Traite Elementaire de Chimie in 1789 and suggested some substances as chemical elements.

Mendelyev (1834-1907) studied the properties of chemical elements, and arranged them in increasing atomic weight (or mass). He discovered the periodicity of chemical properties of elements. His periodic table not only confirmed the elements, but predicted the existences of unknown elements at his time. The periodic table has been a very useful tool for everyone.

Quantum mechanical theory not only explained the arrangement of elements in the Periodic Table, but refined it further leading to today's long form of the Period Table of Elements.

Finding the ultimate root of materials is the spirit of science, and it is also the method of all problem solving. Without knowing the real causes, the suggested solutions are only temporary.

What are the essential properties of elements?

We know an element or a substance by its properties. The following are some of the essential properties of an element: Atomic mass (weight), atomic number, stable isotopes
Atomic radius, ionic radii at their oxidation states
Abundance, distribution, and availablity
Melting and boiling points, vapour pressure at certain conditions
Enthalpies of melting, sublimation, vapourization, etc.
Chemical reactivities: electronic configuration, electronic affinitity, electronegativity, oxidation and reduction potentials
This list is meant for discussion. We have not list all desirable properties of elements, and please add some of your own.

What are main group elements, transition metals, noble gases, lanthanides, and actinides?

Elements in a vertical column is a group. The main group elements are: H, Li, Na, K, Rb, Cs, Fr
Be, Mg, Ca, Sr, Ba, Ra
B, Al, Ga, In, Tl
C, Si, Ge, Sn, Pb
N, P, As, Sb, Bi
O, S, Se, Te, Po
F, Cl, Br, I, At
These elements may be metals or non metals, and their oxidatin states are usually dominated by their group number: +1 +2, +3, +4, +5, +6 and +7 for H, Be, B, C, N, O, and F groups. Oxidation states -1, -2, -4 and -4 are also common for F, O, N, and N groups.

The nobel gases are He, Ne, Ar, Kr, Ze, and Rn. They are all gases, and seldom participate in chemical reactions. However, some compounds of heavy noble gases have been made.

The Lanthanides are elements with atomic number between 57 (La) to 71 (Lu). These are also called rare earth elements. Their typical oxidation state is +3.

The Actinide elements have atomic numbers between 89 (Ac) and 103 (Lr). They have similar properties, but they are all radioactive. Only Ac, Th, and U exist in reasonable amount in nature, due to their long lived isotopes.

Elements in the groups of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn are called transition elements. All these are metal, with various oxidation states. For example, oxidation states of +2 and +3 are common for iron (Fe).

Discuss the relationship between the concept of chemical elements and the atomic theory. What modification is required for the atomic theory in order to explain the existence of isotopes, and modern view of atomic nuclei and electrons?

The discovery of chemical elements led to the atomic theory proposed by John Dalton (1766-1844). He suggested that materials are made up of small indivisible particles called atoms. Different elements consist of different kinds of atoms, and all atoms of an element are the same.

However, the discovery of electrons by J.J. Thomson (1854-1953) already indicated that atoms are divisible. Furthermore, the discovery of radioactivity and its application in the alpha scattering experiment by E. Rutherford and Hans Geiger (1881-1945) revealed the structure of the atom as consists of a tinny heavy nucleus in the center, whose radius is only 100,000th of that of the atom. Since radioactivity is the emission of some particles (including photons) from the atomic nuclei, the nuclei are also divisible. These development have changed Dalton's meaning for the atom, and the change continue as you learn more and more about atomic and nuclear physics and chemistry.

For example, the discovery of protons and neutrons led to the believe that the atomic nuclei are made up of protons and neutrons. The number of electrons in a neutral atom is equal to the number of protons, which incidentally is the atomic number. Atoms of one element, however, may contain different numbers of neutrons. Atoms with the same number of protons but different number of neutrons are called isotopes. The most well known isotopes of hydrogen are H, deuterium (D or 2H) and tritium (D or 3T). The nucleus of H consists of only one proton, but that of D contains a proton and a neutron. Both H and D are stable, and D is present in nature at 0.015 % by number of atoms. The nucleus of a tritium atom consists of a proton and 2 neutrons, and it is radioactive, emitting an electron. In general, the emission of the electron (called beta particle) is believed to be made possible by converting a neutron to a proton.

What are the most abudant elements of the Earth's Crust? In what forms are they present in nature?

The Earth is the 3rd planet of the solar system. We generally divided it into several layers: crust, upper mantle, transition region, lower mantle, outer core and inner core. The crust depth varies between 6 km of deep ocean floor to a thickness of 35 km of the continent.

To understand the abundances of elements of the Earth's crust, a good start is to exame the structure of the Earth's crust. Find some more website that discuss this aspect.

WebElements discusses the abundances of all elements. Summary of the abundances are presented in chart or graphic forms. The three most abundant elements of the Earth crust are oxygen, silicon, and aluminum (aluminium). Because the most abundant mineral of the Earth crust is silicon oxide, SiO2, and alumina AlO2O3. Thus oxygen is the the most abundant element in terms of moles or number of atoms.

Discuss the abundance of anyone element of the Earth Crust. The distribution and abundances of elements of the planet Earth are different from those of the Earth Crust.

What are the most abundant element in the universe, and why?

Abundances of elements in the universe differ very much from that of the planet Earth. In reality, 99% of the mass of the solar system is in the Sun, and the Sun consists mostly of hydrogen. On the Sun, hydrogen are constantly converting to helium in what is known as nuclear fusion. Thus, helium is also abundant in the Sun. In fact, helium was discovered due to its spectrum from the Sun, and the name helium was derived from the Greek word hilios meaning the sun. A NASA website gives the following data on the abundances of some elements of the Sun.
ElementAbundance (% of totalAbundance
number of atoms)(% of total mass)
Hydrogen 91.271.0
Helium 8.7 27.1
Oxygen 0.078 0.97
Carbon 0.043 0.40
Nitrogen 0.0088 0.096
Silicon 0.0045 0.099
Magnesium 0.0038 0.076
Neon 0.0035 0.058
Iron 0.030 0.014
Sulfur 0.015 0.040

A comprehensive diagram of the abundance of elements in the usiverse is given below:

We do not know why hydrogen is so abundant, but why do we recognize hydrogen as the most abundant element in the universe is due to its presence in stars.

To answer the WHY, we need to explore the formation of the universe, and the conversion between matter and energy. The descussion of this is beyond the scope of ionorganic chemistry.

Example 1

Assume that all the deuterium is extracted from natural water in an industrial process. How much water is required in extracting 1.0 L of heavy water, D2O.

Since the atomic or mole abundance of D in hydrogen is 0.015%, the isotope D is tied up as HDO rather than D2O in water. However, the process of extracting heavy water allows D and H to exchange between H2O and H2 and back into H2O again.

If all the deuterium is extracted, 1 L of D2O requires 67 hundred liters.

         100 L H2O
1 L D2O ----------- = 6700 L H2O
        0.015 L D2O

In reality, a lot more than 6700 L is required. Thus, heavy water extraction requires a large supply of water.

Confidence Building Questions