and an introduction to the natural elements
By Dr J Floor Anthoni (2001)
-- seafriends home -- sitemap --Revision dates: 20010323,20070716,
|alkali metals (+1)||alkaline earth metals (+2)||transition metals||other metals||other nonmetals|
|halogens (-1)||noble gases (0)||lanthanides||actinides|
(*) elements have been discovered but have not been named yet.
(+) elements have yet to be discovered.
For an explanation of the coloured groups, see the chapters on atomic structure and chemical properties, below.
|No||Name||Use, where found, importance||No||Name||Use, where found, importance|
Platinum ore, alloys, catalysts
Platiunum ore, alloys, plating, jewelry
Noble metal, conductor, plating, jewelry, photo
Plating, industry, trace element
Zinc ore, plating, semiconductors
Semi-noble, household, alloys, industry, canning
Gold & silver ores, semiconductors
Halogen, trace element, lamps, antiseptic
Noble gas, lights
X-ray shields, medical
|Radioactive element in nuclear
In rocks (apatite)
In rocks (apatite, xenotine)
In rocks (apatite)
Tungsten alloys, electrodes
Resists heat and acis, surgery, electronics
Resists heat, alloys, hot metal, lamps
In molybdenum ores, superconducting alloys
Noblest metal, industry, catalysts, jewelry
Noble metal, industry, jewelry, electronics,
Heaviest liquid metal, thermometers, dentistry
|No||Name||Use, where found, importance||No||Name||Use, where found, importance|
Heavy metal, batteries, gasoline, radiation shield, bullets,
Alloys, trace element
Heaviest halogen, radioactive, *
Radioactive inert gas, radiotherapy,
In uranium & thorium ores
Radioactive element in pitchblende, radiotherapy, research
Radioactive element in pitchblende
Radioactive element in monazite, oxide used in gas mantles
Radioactive element in pitchblende, nuclear fuel
Short-lived radioactive element
Nuclear fuel, nuclear weapons
the periodic table
The periodic table of elements has been credited to a Russian professor of chemistry, Dmitri Ivanovich Mendeleev (1869). At the time it included 63 known elements arranged to increasing atomic weight. The periodicity of chemical elements had not been left unnoticed before and in 1787 already, Antoine Lavoisier and others noticed the regularity in the 33 elements then known to exist.
Rapid progress happened in
the early part of the 20th century: In 1911 Ernest Rutherford developes
the theory of an electrically charged nucleus and electrons around it.
In 1913 Niels Henrik Bohr formulates how atoms are structured with a heavy
nucleus of neutrons and protons, surrounded by various shells of electrons.
In 1914 Henry Moseley formulated that the correct sequence was not based
on mass but on the number of protons. In 1930 Linus Pauling formulated
the chemical laws that describe chemical bonding between elements, and
so the basis for chemistry as it is still valid today, was laid. For over
80 years, the periodic table of elements has survived an avalanche of scientific
discoveries and refinements. Functioning as a unifying principle, it is
probably here to stay forever, and some knowledge of this table and the
elements of life would greatly help to understand the processes of nature.
forms of periodic table
The first periodic tables in use were only 8 columns wide, corresponding to the main properties of the elements, as discussed below. As more and more elements were found, the table had to be widened, thereby losing some of its clarity. The pyramidal table on right (developed by William B Jensen) more reflects the lengths of the periods, starting with two, then 8, then18, then 32. The black lines join elements with the same type of outer shell of electrons. (Source: Eric R Scerri, The evolution of the periodic system, Sci Am Sep 1998)
structure of an atom
It is quite difficult to imagine that every atom of every substance known, consists of a heavy nucleus of protons and neutrons, surrounded by a vast amount of space around which clouds (shells) of orbiting electrons. The nucleus is about 10,000 times smaller than the shell, which is 1E-10 to 6E-10m. Imagine the nucleus as large as a golf ball, then the electrons would circle around it at a distance of 550m! A golfbal composed only of neutrons would weigh 4E10 tonnes without the space surrounding each nucleus.
Protons and neutrons have identical mass of one unit, but protons are positively charged with one unit of electricity. Protons would repel one another had there been no neutrons. All stable elements have about as many neutrons as protons (ratio 1/1) but the heavier elements have more neutrons (ratio 3/2). The first element is Hydrogen, having only one proton in its nucleus, and thus an atomic mass of 1.
The unit of atomic mass is defined as one twelfth that of carbon-12 (12C), which makes the mass of a proton=1.007277u, a neutron=1.008665u and an electron=0.000549u. The table shows that all elements do not appear to have precise masses, composed of precise units. This is because each elements has one or more isotopes, atoms with the same number of protons but a different number of neutrons. For Hydrogen, there also exists Deuterium (1 proton, one neutron) and the unstable elementTritium (one proton, two neutrons). There are three times as many stable isotopes as the number of boxes in the periodic table, while the number of unstable isotopes is much larger still (over 1500).
For every proton there is an electron, to balance the electric charge. Although electrons have some mass, it is negligible compared to that of protons and neutrons. Electrons are attracted by the protons but because of their speed in orbits at some distance, they do not fall to the nucleus. There is no friction in the movements of either protons, neutrons or electrons.
The first shell (H and He) can hold only two electrons (2x1x1). The second shell (Li - Ne) eight (2x2x2), the third 18 (2x3x3), the fourth 32 (2x4x4), the fifth 50 (2x5x5). Within each shell, finer divisions are recognised. The shells do not fill up incrementally but according to the laws of quantum mechanics. Traditionally, these shells are named with the letters K,L,M,N,O.
It is the structure of the outer shell of electrons that gives each element its chemical characteristics, hence the eight columns in the periodic table.
properties of elements
The periodic table's columns and rows reflect the way the electrons fill the outer shell. Each new row is a new shell, whereas the eight columns (leaving the violet transition metals and yellow lantanides out), count the number of electrons in the outer shells. In the discussion below, only eight columns are considered, thus columns 13-18 in the periodic table become 3-8.
The chemical properties of the elements depend mainly on the number of electrons in their outer shells. Going from left to right through the eight columns, this makes one for for Lithium, two for Beryllium and so on, seven for Fluorine and the full house for Neon. All elements in the eighth column belong to the noble gasses (He, Ne, Ar, Kr, Xe). Their outer shells are so perfectly filled that thy do not easily share an electron, hence their chemical inertness.
By contrast, elements in column one (H, Li, Na, K) have a lonely electron in their outer shells, which is easily shared. Their 'strength' or valence is said to be +1. Likewise all elements in column seven (F, Cl, Br, I) come one electron short of a full-house configuration, which gives them a valence of -1. It comes as no surprise then that combinations of elements from these two columns make strong 'electrovalent' chemical bonds like NaCl (common salt). To bind an element of column 2 (valence +2) requires two of column 7 (valence -1), like MgCl2 (magnesium chloride). Underneath the periodic table, the names of the groups of elements and their valence can be found. The missing ones are: Column 13 valence +3: B, Al, Ga; column 14 valence +4: C, Si, Ge, Sn, Pb; column 15 valence -3: N, P, As, Sb; column 16 valence -2: O, S, Se. The group of transition elements have properties in between those left and right to it.
Atoms can share their outer electrons in various ways to form bonds. The covalent bond binds two atoms of same valence, like the gases H2 and Cl2 into molecules. Other kinds of chemical bonding occur and their strengths depend on many factors, like how many electrons are in the inner shells, the size of the atom, geometric arrangement and so on.
This is not the place for
a course in chemistry, but a little understanding will help to better grasp
the contents of other chapters on this web site.
When the nucleus, consisting of protons and neutrons, is not in balance, an atom may disintegrate in several possible ways, emitting radioactive radiation:
Isotopes of small atoms with a shortage of neutrons, may convert a neutron into a proton by emitting a positron (positively charged kind of electron), which is immediately annihilated by an electron, producing gamma radiation. Some neutron-deficient small atoms may also capture an electron from its own shell, the place of which is filled by an electron from an outer shell, producing Roentgen (X-ray) radiation. Gamma radiation is the highest energy electromagnetic radiation, known. It penetrates deep into all substances. X-rays are less energetic, being stopped by heavy elements like lead, barium and others.
Isotopes of small atoms with an excess of neutrons may convert a neutron to a proton by emitting an electron (beta radiation). This converts the atom into an isotope with different properties. Thus radio-active Carbon-14 becomes Nitrogen. Beta radiation does not penetrate very far (in air a few cm), while easily stopped by a metallic film.
Heavy isotopes with more than 82 protons in their nuclei can atain a stable configuration by ejecting a Helium nucleus of 2 protons and two neutrons. This is called alpha radiation. Alpha radiation, because of its large size, does not penetrate far, but causes much radiation damage when ingested. The element Radium decays into Radon gas by emitting an alpha particle.
Very heavy nuclides can undergo
into two or more fragments with the release of several neutrons and a very
large amount of energy. Uranium-235 when capturing a neutron, converts
to Uranium-236 and Strontium-90 and Xenon-143, emitting 3 neutrons (which
can be captured by other Uranium nuclei) and 200 MeV energy. This is a
very large amount of energy, 50 million times larger, than the energy released
from burning carbon-fuels: C + O2 = CO2 + 4 eV.
Radioactivity is a natural process in the formation of stars, suns and planets. Those elements that decay rapidly, have over the eons of time, disappeared but some natural long-lived radioactive elements are still found on Earth. Radioactivity is also caused by the sun's radiation, interacting with Earth's atmospheric gasses. These natural radioactive elements have enabled scientists to determine the dates of rocks, fossils and human artefacts.
Humans create radioactive elements inside nuclear reactors and for scientific purposes. In order for isotopes to be useful as scientific tracers, they must have a reasonable shelf life, purity and radio activity and play a role in biological processes. Here is a list of the most common radioactive isotopes that matter to life on Earth.
Note the notations for a=alpha
b=beta c=gamma p=positron x=x-ray y=year d=day h=hours s=seconds. The E
notation is used for exponents of ten: 100 = 102 = 1E2. (?)=
table below lists which nutrients are thought to be essential to various
nutrient deficiency in plants
Plants are the basis of all life. They are also the first creatures to have evolved on land, where water and nutrients are much harder to acquire. Plants depend on the macro nutrients N, P, K, S, Mg, Ca and a number of micro nutrients (trace elements). From these nutrients and carbon dioxide, plants manufacture a vast range of biochemical compounds necessary for themselves and for other organisms.
Nitrogen is taken up by plants as nitrate (NO3-) or ammonia (NH4+) ions. Bacteria in the soil, often living close to plant roots, are able to convert the abundantly available nitrogen gas (N2) into nitrates or ammonia. Also nitrates and nitrogen compounds are manufactured in the atmosphere by ultraviolet radiation, raining down equally on land and sea. These critically important nutrients are absorbed on clay particles and humus.
The plant incorporates nitrogen in organic compounds, mainly proteins and nucleic acids, essential components of protoplasm and enzymes. The compounds are accumulated in the living parts of the plant: the shoots, leaves, buds and storage organs. Lack of nitrogen results in stunting or dwarfism, spindly appearance; yellowing of old leaves, sometimes reddening; more roots than shoots.
Phosphates are taken in as organically bound phosphates of Ca, Fe, Al, in the relatively insoluble PO4-- or HPO4- ions. It is incorporated in esteric compounds, nucleotides, phosphatides, phytin, essential for basic metabolism and photosynthesis. It accumulates in reproductive organs (pollen) and in leaves. Lack of phosphorus disturbs the reproductive process (delayed flowering), stunting, dark green or bronze leaf discolouring and needle-tip drying in conifers.
Sulfur comes from sulfur-containing minerals of Ca, Mg, Na. The SO4-- ion is readily absorbed and does not adsorb onto clay. Inside the plant it is used to produce esters, proteins, coenzymes and others, essential components of cell protoplasm. It accumulates in leaves and seeds. Lack of sulfur causes symptoms similar to nitrogen deficiency.
Potassium is found in the minerals feldspar, mica and clay. It is available as the K+ ion, which is strongly adsorbed to clay. In the cell sap, potassium promotes hydration, and acts in balance with other ions. It is necessary for enzyme activation in: photosynthesis, nitrate reductase, osmoregulation. It accumulates in young tissue, bark and sites of intense metabolism. Lack of it results ina disturbed water balance (dying tips), curling of edges of older leaves, root rot and in conifers, premature drop of needles.
Magnesium is found in soil carbonates (dolomite), silicates (augite, hornblende, olivine), and as sulfate chloride. It is readily adsorbed to clay and thus deficient in acid soils. Absorbed as the Mg++ ion, it is bound in chlorophyll, pectates, components of enzymes and ribosomes. Accumulating in leaves, it is essential for the regulation of hydration and metabolism: photosynthesis and phosphate transfer. Lack of Magnesium results in stunted growth, interveinal chloroses of old leaves.
Calcium is found in soils as carbonates (gypsum), phosphates and silicates (feldspar, augite). It is strongly adsorbed to clay and deficient in acid soils. Absorbed by the plant as the Ca++ ion, it is organically bound in pectates which regulate hydrates. Calcium is an enzyme activator and regulator of length-wise growth. It accumulates in leaves and bark. Lack of calcium disturbs growth (small cells), tip drying, leaf deformation and impaired root growth.
Iron is available in soil as sulfides, oxides, phosphates, silicates (augite, hornblende, biotite). It is adsorbed to clay and forms an important part of clay structure. It is deficient in acid soils. As the Fe++ ion or Fe+++chelate, it takes part in metal-organic compounds as components of enzymes (heme, cytochrome, ferredoxin). Iron plays an important role in basic metabolism (redox reactions), nitrogen metabolism and photosynthesis. It accumulates in leaves and lack of it shows as straw-yellow interveinal chloroses; in extreme cases white coloration of young leaves and suppressed formation of apical (top) buds.
(source: W Larcher, Physiological
plant ecology, 1980, Springer Verlag)
Nutrients, minerals or trace elements are needed by the human body. When deficient, disease symptoms appear. In order to better understand the importance of various elements, the most common deficiency symptoms follow below.
Iron deficiency anemia
Chlorine is available in table salt, a common component of human blood (60%). Chlorides play an essential role in the neutrality and pressure of extracellular fluids and in the acid-base balance of the body. Hydrochloric acid is produced in the stomach for the digestion of food. it is also lost in sweat, urine and faeces (92%). The body's supply of chlorine can deplete rapidly through excessive perspiration or loss of acid in the body.
Chlorine is found in table salt but also in dairy food, fish and eggs. Vegetables may be low in salt.
Cobalt is a trace mineral bound to the vitamin B12. The pancreas contains a high concentration of the metal for the production of insulin and other enzymes for metabolising carbohydrates and fat. It is interesting to note that vitamin C counteracts cobalt.
Cobalt is absorbed from foods grown on soils with high concentrations of it. Vitamin B12 is found only in animal foods, so that vegetarians and vegans run a high risk of cobalt deficiency.
Copper is an element necessary for oxydation and absorption of iron and vitamin C. It also acts as a catalyst for making hemoglobin. The highest concentrations of it are found in the liver. Copper deficiency symptoms are similar to anemia.
Sources of supply: animal flesh, particularly liver, oysters, fish, whole grains, nuts and legumes.
Although fluorine is a poison in higher doses, it is necessary for retaining calcium in teeth and bones. Fluoride compounds are artificially added to municipal water supplies in order to reduce the incidence of caries (tooth rot).
Iodine is important in the thyroid gland that controls heart action, nerve response to stimuli, rate of body growth and metabolism. A deficiency of it leads to goitre, an enlargement of the thyroid gland, a disease common in areas remote from salt water. Early symptoms are: dry skin, loss of hair, puffy face, flabbiness, weak muscles, weight increase, diminished vigour and mental sluggishness. A sufficient supply of iodine during pregnancy is important to prevent cretinism (retarded mental & physical development).This deficiency can be prevented by eating seafood regularly or by using iodised salt.
Magnesium is essential to enzyme reactions in the metabolism of ingested carbohydrates. About 75% of it is associated with skeleton and tooth formation. The remainder (25%) is found in soft tissues and body fluids. Although its role is not precisely known, it is important in the functioning of cell membranes and the stimulation of muscles and nerves.
Magnesium deficiency symptoms are: chronic kidney disease, excess acid, diabetic coma. Lighter symptoms could include: weakness, dizziness, distension of the abdomen and convulsive seisures.
The best food sources are: cereals, legumes, nuts, meat, fish, and dairy products.
Manganese is known to be a catalyst in the action of calcium and phosphorus and it is essential for normal bone structure.
Principal food sources are: legumes, nuts, whole-grain cereal, tea and leafy vegetables.
Phosphorus is a mineral vitally important to the normal metabolism of numerous compounds. About 70% combines with calcium in the bones and teeth, while nitrogen combines with most of the remaining 30% to metabolise fats and carbohydrates. Phosphorus is the main element in the structure of the nucleus and cytoplasm of all cells and functioning of enzymes.
Symptoms are rickets in children and osteoporosis in adults, severe muscle spasms in fingers and toes.
Phosphorus is found in dairy products, egg yolk, fresh food, legumes, nuts and whole grains.
Potassium is an essential constituent of cellular fluids. It maintains the intracellular fluid balance. It is also important in the metabolism of nitrogen compounds (proteins) and its working depends on calcium and sodium. Potassium is important for normal muscle and nerve responsiveness, and heart rhythm. Only about 8% of potassium's daily intake is retained; the rest is excreted.
Potassium deficiency occurs particularly through food starvation. It is also excreted rapidly in severe diarrhea, diabetes, and prolonged administration of cortisone medications.
Almost all foods contain adequate amounts of this mineral.
Sodium is an element that functions with chloride and bicarbonate to maintain the balance of positive and negative ions in body fluids and tissues. Sodium has the property of holding water in body tissues. Excess sodium may result in edema or water retention. Too little of it disturbs the tissue-water and acid-base balance, necessary for good nutritional status. The hormone aldosterone controls the balance of sodium and water in the body.
Symptoms may include feelings of weakness, apathy, nausea, cramps. Sodium is found in all foods and table salt.