INORGANIC CHEMISTRY
INORGANIC CHEMISTRY
GLOSSARY
allotropes Two or more forms of the same element, but with different structures (and therefore different properties).
catalytic properties To have the ability to act as a catalyst (a substance that increases the rate of chemical reaction without being consumed by the reaction).
CFCs Chlorofluorocarbons. These compounds were common in air conditioning and refrigeration, but are now banned due to their harmful effect on the Earth’s ozone layer.
colour wheel A circle or wheel that contains different colours and shows how they are related. You can use a colour wheel to predict the colour of an object based on what colours the object absorbs.
complementary colours Two colours opposite each other on a colour wheel. Complementary colours have high contrasts between one another.
complex (transition metal complex) A compound or ion consisting of a transition metal linked to one or more ligands.
concatenated atoms Atoms that have been linked to form a chain structure.
crystal field theory (also ligand field theory) A bonding theory in inorganic chemistry in which ligands donate an electron pair to a central metal ion.
diffraction grating A surface engraved with a series of closely spaced lines that reflects different wavelengths of light at different angles. Diffraction gratings can split white light up into its constituent colours.
electromagnetic spectrum The range of frequencies of electromagnetic radiation bounded by radio waves at low frequencies and gamma rays at high frequencies.
fuel cell An electrochemical cell that produces electrical current from the continuous input of a fuel.
fullerenes Carbon molecules that have spherical, tubular or other similar structures.
graphene A form of carbon consisting of a sheet of carbon atoms one atom thick.
graphite A form of carbon composed of carbon atoms bound together in sheets, which are stacked on top of one another.
ligand A molecule or ion that donates an electron pair to a central metal ion in transition metal complex.
metalloid An element that falls along the boundary between metals and non-metals on the periodic table. Metalloids have properties intermediate between metals and non-metals.
oxidation state The charge an atom would have in a chemical compound if all of the bonding electrons were assigned to the more electron negative atom (the atom that most strongly attracts electrons).
photosynthesis The process by which plants convert carbon dioxide, water and sunlight into glucose and oxygen.
prism A clear optical element that is usually triangular in shape and can bend light of different wavelengths by different amounts. When white light travels through a prism, it is broken up into its constituent colours.
reactant Any one of the substances that undergoes a chemical reaction. In a reaction, reactants react to form products.
silicate Compound containing silicon, oxygen and sometimes various metal atoms. Silicates form network covalent structures with high melting points.
stratosphere An atmospheric layer that begins about 10 km (just over 6 miles) above the Earth’s surface and is sandwiched between the troposphere below and the mesosphere above.
substrate The molecule on which an enzyme (a biological catalyst) acts.
transition metals Those metals found in the large centre block of the periodic table (the d-block). Transition metals (in contrast to main group metals) tend to have properties that are less predictable based on their exact position on the periodic table.
valence electrons The highest energy electrons (and therefore the most important in bonding) in an atom.
Zintl ions Ionic clusters of main group elements.
THE UNIQUENESS PRINCIPLE
the 30-second chemistry
The periodic table contains a dividing line that is never marked. The invisible line occurs between the table’s second and third rows, where boron meets aluminium; carbon meets silicon; and so on until fluorine meets chlorine. Elements above the line cannot form bonds to as many atoms as those below the line, being strictly limited to a total of eight ‘valence’ or bonding-level electrons. Thus, while oxygen forms the mono- and dioxides with itself (that is, O2 and O3), sulfur, selenium and tellurium form mono-, di- and trioxides, of which SO, SO2 and SO3 are examples. Similarly, nitrogen forms the trichloride NCl3 while phosphorous, arsenic and antimony form both tri- and pentachlorides such as PCl3 and PCl5. However, unlike later elements, the non-metals of the second row are small enough to form strong multiple bonds, a quality that enables them to form compact molecules where a heavier element would form an extended structure of linked atoms. Carbon, for instance, forms the triple and doubly bonded oxides CO and CO2, while its heavier counterparts – silicon, germanium, tin and lead – react with oxygen to form three-dimensional solid networks held together exclusively by single bonds.
3-SECOND NUCLEUS
Elements in the periodic table’s second row behave differently from heavier elements because they form strong multiple bonds and are limited to eight valence electrons.
3-MINUTE VALENCE
One consequence of the uniqueness principle is that planetary atmospheres largely consist of first- and second-row elements. Earth’s atmosphere is comprised mostly of nitrogen and oxygen; Mars’s atmosphere mostly of CO2; and those of the gas giants are mostly hydrogen, helium, CH4 and NH3. In contrast, the planetary crusts of planets such as Earth and Mars contain large amounts of silicate minerals, many of which contain chains, sheets and 3D networks held together by silicon-oxygen single bonds.
RELATED TOPICS
See also
THE LEWIS MODEL FOR CHEMICAL BONDING
CARBON: IT’S NOT JUST FOR PENCILS
3-SECOND BIOGRAPHIES
VICTOR GOLDSCHMIDT
1888–1947
Swiss crystal chemist who classified elements by their dominant geologic locations
THOM DUNNING
1943–
American chemist who explained first-row anomalies in terms of recoupled pair bonds
30-SECOND TEXT
Stephen Contakes
The second-row elements are unique – they are very different from the elements that lie below them in the periodic table.
COLOUR
the 30-second chemistry
When white light passes through a prism, the light is dispersed into a spectrum of colours. The colours range from red at the lowest frequencies through orange, yellow, green, blue and finally violet at the highest. Substances that absorb all frequencies of visible light appear black, while substances that reflect all frequencies of visible light appear white. Coloured objects appear to an observer to have a colour because they absorb certain frequencies (or wavelengths) of visible light while reflecting or transmitting (allowing to pass) others. The precise colour a substance has depends on which frequencies are absorbed. In general, a substance will appear to have a colour complementary to the one absorbed (and opposite it on a colour wheel). For example, a substance that appears yellow absorbs violet light (the complement of yellow). Transition metal complexes are often deeply coloured because they strongly absorb certain frequencies of light in the visible region. These complexes often have unfilled outer-level orbitals that can receive an electron excited by specific frequencies of visible light. The colour absorbed depends on the separations between the d-orbitals, which in turn depend on the ligands attached to the metal.
3-SECOND NUCLEUS
Coloured objects appear to have colour because they absorb some frequencies of visible light and reflect or transmit the others.
3-MINUTE VALENCE
Our eyes can detect a narrow range of frequencies in the electromagnetic spectrum. This range of frequencies is responsible for all of the colours that we see. Our brains have evolved to use colour as a way to help distinguish one substance from another. Modern spectrometers, which precisely measure the frequencies absorbed by substances, are among the most powerful scientific tools in substance identification.
RELATED TOPICS
See also
3-SECOND BIOGRAPHIES
ALFRED WERNER
1866–1919
Swiss chemist who won the 1913 Nobel Prize in Chemistry for predicting the three-dimensional structure of many transition metal complexes before modern structural methods
JOHN HASBROUCK VAN VLECK
1899–1980
American physicist who won the 1977 Nobel Prize in Physics and was instrumental in the development of crystal field theory, the precursor to ligand field theory
30-SECOND TEXT
John B. Vincent
White light separates into its component colours when passed through a prism.
CLUSTER CHEMISTRY
the 30-second chemistry
In some molecules, ions and materials the electrons that hold the atoms together are shared between a group of clustered atoms. For instance, some metals and metalloids can be reduced to liquid-soluble fragments of metal while many transition metals form clusters when combined with chlorine, sulfur or carbon monoxide under the right conditions. Some of the latter clusters catalyze commercially important reactions, although none has yet found industrial use. Sometimes clusters exist as discrete units; in other cases they are linked together in a network. Solid MoCl2, for example, consists of octahedral clusters of Mo6Cl84+ bridged by intervening Cl- ions. However, when heated in the presence of additional chloride, the connections are broken to give discrete Mo6Cl142- units. The ratio of electrons to atoms in a cluster affects its shape. When clusters have just enough electrons to hold together, they form as compact a shape as possible – that of the smallest polyhedron that can accommodate all the core atoms. In contrast, clusters with more electrons tend to open up and take on the shape of larger polyhedra with unoccupied vertices, giving clusters that sometimes look like a molecular nest or a web.
3-SECOND NUCLEUS
Cluster compounds form when atoms and ions share electrons and bunch together in a polyhedral shape.
3-MINUTE VALENCE
Many of the most important reactions for life on Earth are facilitated by metal-containing clusters located within proteins. For example, clusters containing iron and sulfur facilitate the movement of electrons through many biological systems, including the respiratory chain our cells use to harvest energy by converting oxygen to water. In photosynthesis plants reverse this process, harvesting even more energy from sunlight to produce oxygen at a cluster containing four manganese ions and one calcium ion.
RELATED TOPICS
See also
WHERE ELECTRONS ARE WITHIN AN ATOM
THE LEWIS MODEL FOR CHEMICAL BONDING
3-SECOND BIOGRAPHIES
WILLIAM N. LIPSCOMB
1919–2011
American chemist who pioneered study of the structure and bonding in borane clusters
KENNETH WADE
1932–2014
British chemist who developed ‘Wade’s Rules’ for predicting cluster compounds’ shapes and stability
30-SECOND TEXT
Stephen Contakes
Cluster compounds have polyhedral shapes and unique properties.
TRANSITION METAL CATALYSTS
the 30-second chemistry
Many industrial chemicals are produced by combining small organic molecules or substrates with catalysts composed of transition metals (such as cobalt, chromium or iron) which are themselves bound to small molecules called ligands. In these processes the metals speed up reactions between the substrates by acting as platforms where substrates can bind and then break into smaller molecular fragments, rearrange how their atoms are bound together and form new bonds with other substrates. The new molecules and fragments that result can then be released from the metal to yield the reaction products and regenerate the original metal complex. In fact, from the viewpoint of the metal the entire process involves a cyclic series of reactions or ‘catalytic cycle’ in which the metal complex adds reactants and spits out products. Some metal catalysts do not even need to bind their substrates, but instead function by pushing electrons around. For instance, some biological iron clusters facilitate the movement of electrons between reactants, alternatively gaining an electron from one substrate and passing it to another. Other complexes can harvest energy from light and use it to push electrons into or out of molecules, generating unstable intermediates that then quickly react with other nearby molecules.
3-SECOND NUCLEUS
Transition metal compounds facilitate chemical reactions between small molecules that bind to the metal, rearrange and get released as new products.
3-MINUTE VALENCE
Many biological and industrial processes involve transition metals acting as catalysts, substances that speed up chemical reactions without being changed themselves. Without metal catalysts we could not use the oxygen we breathe or produce enough food to sustain current population levels. Perhaps we wouldn’t even be around today, because one hypothesis about the origin of life involves catalysis by iron minerals.
RELATED TOPICS
See also
REACTION RATES & CHEMICAL KINETICS
3-SECOND BIOGRAPHIES
HUMPHRY DAVY
1779–1829
British chemist who discovered that platinum was useful as a heterogeneous catalyst
KARL ZIEGLER & GIULIO NATTA
1898–1973 & 1903–79
German and Italian chemists who developed a catalyst for making commercial plastics with specific properties
30-SECOND TEXT
Stephen Contakes
Transition metal compounds can act as catalysts in chemical reactions.
CARBON: IT’S NOT JUST FOR PENCILS
the 30-second chemistry
The major common allotropes of carbon include shiny, transparent and super-hard diamond and soft black graphite. Graphene (isolated in 2010 by Andre Geim) is a one-atom-thick sheet of carbon atoms densely packed into a chicken-wire-shaped structure. Graphite is many sheets of these graphene layers stacked together. Since these layers are only weakly bound to each other they are readily rubbed off onto paper and therefore used in pencils. In 1985, Harry Kroto discovered a new form of carbon (C60) when he and his colleagues Richard Smalley and Robert Curl simulated chemical reactions that might occur in the atmosphere of red giant stars. C60 is one of a larger family of carbon forms known as fullerenes. Fullerenes are molecules in the form of hollow spheres, ellipsoids or cylinders. Since C60 looks much like the famous geodesic domes of R. Buckminster Fuller, it was dubbed ‘buckminsterfullerene’. Spherical or ellipsoidal fullerenes are fondly known as ‘buckyballs’. Graphene layers can also wrap around and form cylindrical tubes called ‘nanotubes’ or ‘buckytubes’. Fullerenes are flexible, strong and stable, with an ever-increasing number of practical uses – for example, as catalysts, in energy generation and storage devices, as MRI and X-ray contrast agents and in flexible electronics.
3-SECOND NUCLEUS
Carbon allotropes include diamond, graphite and fullerenes. Fullerenes, named after Buckminster Fuller, come in the form of hollow spheroids (‘buckyballs’) and nanotubes (‘buckytubes’).
3-MINUTE VALENCE
Carbon is a unique element. Not only is it the central element on which all life is based, but in its elemental state it also exists in several fascinating and useful allotropes (different molecular forms of a given element).
RELATED TOPICS
See also
THE LEWIS MODEL FOR CHEMICAL BONDING
THE FORCES THAT HOLD MATTER TOGETHER
3-SECOND BIOGRAPHIES
R. BUCKMINSTER FULLER
1895–1983
American inventor, architect and author who popularized the geodesic dome
HARRY KROTO
1939–2016
English chemist, winner of the 1996 Nobel Prize in Chemistry for discovering fullerenes
30-SECOND TEXT
Glen E. Rodgers
Carbon comes in many forms including familiar graphite and new forms such as graphene.
NANOTECHNOLOGY
the 30-second chemistry
Nanotechnology is the study of matter where the basic structure has at least one of its dimensions less than or equal to 100 nanometres (1 nanometre is one-billionth of a metre.) This would therefore include almost all of chemistry, since most molecules meet such a requirement. However, what is different about nanochemistry is that it uses bottom-up molecular routes to reach the larger domains, coupling molecule to molecule to make larger structures. This is in contrast to the traditional top-down approaches in which large structures are cut into smaller pieces. The bottom-up route permits the precision of chemical synthesis to affect larger materials properties. As an example of this bottom-up approach, different molecules that are about 0.1 nanometre in size can be attached together using synthetic chemical techniques to make tiny structures such as nanocars. A single nanocar is 2 nm x 3 nm in size with four wheels, fully rotating axles, chassis and light-activated motors. These nanocars may be able to perform work, such as bringing in molecules or atoms through selective voltage pulse commands to further construct larger entities or to deliver drugs to cells. Molecularly built nanocars are so small that 25,000 of them lined up end to end would only span a distance the diameter of a human hair.
3-SECOND NUCLEUS
Nanotechnology is the science of building tiny structures from the molecular size up.
3-MINUTE VALENCE
Nanochemistry can also be used to construct nanoparticles of precise size and shape with unique catalytic properties for processes such as converting hydrogen and oxygen to water in a fuel cell to generate electricity. Other nanoparticles can be used to split water, using sunlight, to the requisite hydrogen and oxygen needed by the fuel cell. Combined, such a system could potentially supply the world’s energy needs in a far cleaner manner than using fossil fuels – as we do today.
RELATED TOPICS
See also
CARBON: IT’S NOT JUST FOR PENCILS
3-SECOND BIOGRAPHIES
RICHARD FEYNMAN
1918–88
American physicist who first suggested building molecular structures one atom at a time; he won the 1965 Nobel Prize in Physics
RICHARD SMALLEY
1943–2005
American chemist and foundational figure in nanotechnology who was awarded a share of the 1996 Nobel Prize in Chemistry
30-SECOND TEXT
James Tour
Molecular machines such as nanocars have the potential to perform vital tasks in medicine and energy supply.
