Structural Biochemistry/Poor Metals
The Poor Metals are:
- Aluminium (Al)
- Gallium (Ga)
- Indium (In)
- Thallium (Tl)
- Tin (Sn)
- Lead (Pb)
- Bismuth (Bi)
The poor metals are located in the p-block, and are the most electronegative but least reactive  of all the metals. They are softer than the transition metals, but cannot be classified as metalloids. 
Poor metals also go by the name Post-transition metals. These are elements to the right of transition metals. Poor metals is considered the trivial name for such elements meaning Post-transitional metal name is preferred. Characteristics of poor metals are due to where they lay in the periodic table of elements. Their melting and boiling points are generally lower than normal metals. Their electronegativity and conductivity is also higher, but their texture is softer than usual metals. These elements are distinguished by metalloids by their high boiling points compared to that row of elements in the periodic table. 
The third most abundant element on the earth is a light, strong metal that has several types of alloys. One of its alloys is duraluminum, which is stronger than pure aluminum and resistant to corrosion. It contains other elements such as copper, manganese, magnesium, and silicon. It is used for airplane construction and electrical wires.
Aluminum is harmful to the body since it can damage all types of tissues. It is considered a a neurotoxin and protoplasmic poison, meaning that a healthy cell will be damaged or killed as a result of exposure to the aluminum. There has been evidence that accumulation of aluminum can contribute to the cause of Alzheimer's disease. Some research has shown that degeneration of nervous tissue from aluminum in animals are similar to the way the brain degenerates in Alzheimer's disease. Experimentation from Toronto University have shown that Alzheimer's disease patients that were given treatment for the removal of aluminum showed a decrease in the rate of degeneration.
At the molecular level, aluminum sticks to phosphates of our DNA. Other toxic metals, such as mercury and lead, stick to the phosphates as well. However, the biological system has sticky chelators that can remove the toxic metals and send it to the kidney to be detoxified. Aluminum is considered a toxin because it cannot be easily removed from the phsophate, even with chelators. Once it sticks to the phosphate of the DNA, it will stay there until the cell dies.
Some symptoms of aluminum poisoning include forgetfulness, inability to concentrate, and even dementia.
Gallium becomes a liquid at a low melting point of 29.8°C. It is a blue-gray metal that can expand upon freezing. Gallium does not exist in it's pure form in nature, and commonly found in lead. Gallium is useful as a semiconductor and has similar properties as aluminum. It can also be used to produce mirrors, and is often used in circuits. Pure Gallium does not seem to have any effect on human health, there are traces in the body, and water with traces also seems to have no effect. Gallium compounds on the other hand can be very harmful.
The melting point of indium is 156.61 °C, boiling point is 2080 °C, specific gravity is 7.31 (20 °C), with a valence of 1, 2, or 3. Indium is a very soft, silvery-white metal. The metal has a brilliant luster and emits a high pitched sound when bent. Indium wets glass. Indium may be toxic, but further research is required to assess its effects.
Thallium is a chemical element with atomic number 81, atomic weight 204.37, and symbol Tl. It is a heavy, bluish metal that looks much like lead, it is soft and melts with ease. It will react with oxygen fairly easily, forming a layer of thallium oxide. Approximately two dozen radioactive isotopes of Thallium have been produced. Thallium -201 can be used by doctors to diagnose how well a person's heart is operating. It used to be used as a rodent killer, it is colorless and odorless, so it when undetected to the unsuspecting small animals. But it was soon realized it could no longer be used because of it's detrimental effects on human's health. Its salts are active poisons that may cause alopecia, liver and kidney damage, blindness, and neurologic and psychic symptoms such as ataxia, restlessness, delirium, hallucinations, delusions, and semicoma. Recently it has been looked into as a superconductior, which allows an applied current to pass through it forever.
Tin has a melting point of 231.9681°C, boiling point of 2270°C, specific gravity (gray) of 5.75 or (white) 7.31, with a valence of 2 or 4. Tin is a malleable silvery-white metal which takes a high polish. It possesses a highly crystalline structure and is moderately ductile. When a bar of tin is bent, the crystals break, producing a characteristic 'tin cry'. Two or three allotropic forms of tin exist. Gray or a tin has a cubic structure. Upon warming, at 13.2°C gray tin changes to white or b tin, which has a tetragonal structure. This transition from the a to the b form is termed the tin pest. A g form may exist between 161°C and the melting point. When tin is cooled below 13.2°C, it slowly changes from the white form to the gray form, although the transition is affected by impurities such as zinc or aluminum and can be prevented if small amounts of bismuth or antimony are present. Tin is resistant to attack by sea, distilled, or soft tap water, but it will corrode in strong acids, alkalis, and acid salts. The presence of oxygen in a solution accelerates the rate of corrosion.
Lead is virtually ubiquitous in the environment as a result of its natural occurrence and its industrial use. Potential symptoms of overexposure to lead are anorexia, abdominal pain, colic, anemia, paralysis of wrists or ankles, kidney disease, and hypotension. Exposure to lead occasionally produces clearcut, progressive mental deterioration in children. Very low concentrations of lead interfere with the activity of δ-aminolevulinate dehydratase, and ferrochelatase during the biosynthesis of heme.
Bismuth has the symbol Bi. It has an atomic number of 83 and its atomic weight is 208.98. It has a melting point of 544.4K and a boiling point of 1837K. In early times bismuth was confused with tin and lead. Claude Geoffroy Jr. showed it to be distinct from lead in 1753.
"Gallium." Water Treatment Solutions. Lenntech. 2011. http://www.lenntech.com/periodic/elements/ga.htm
Goodman, Louis S, and Alfred Goodman Gilman. The Pharmacological Basis of Therapeutics. 7th ed. New York, N.Y.: Macmillan, 1985.
- Post-transitional metals, November 14th, 2012.