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Introduction: Minerals, Elements, and Compounds
Nutrition books are often confusing when they discuss human nutrient requirements. For example, one, in discussing essential minerals in sports nutrition says "Minerals are elements". But only one common essential mineral, iron (symbolized Fe for the Latin "Ferrum") is commonly ingested as an element. Iron is an element because it is made up of a single kind of atom, designated by the symbol Fe. Other symbols are given in the Table below. Iron metal particles are actually found in breakfast cereals, and the easiest way to prove it is to float a cereal flake on water and pull it around with a magnet. You can also see it extracted in several YouTube videos like this one. Sometimes iron is added as a compound, like "ferrous sulfate", FeSO4. A compound has atoms of several elements bonded together is specific ratios. The ratios are given by the subscripts in the formula; in this case, ferrous sulfate is made from 1 atom of iron, 1 of the element sulfur, and 4 atoms of the element oxygen.
Another essential mineral that is commony misidentified is "iodine". The nutrient we actually ingest is not the element iodine, but a compound of iodine like potassium iodide, KI (K is the symbol for potassium, after the German Kallium).
While the mineral KI looks and tastes like table salt, the element iodine is a dark purple (almost black) solid, sometimes dissolved in alcohol to give a brown solution used to disinfect minor wounds. It's a toxic element with the formula I2<, showing that an element may be made up of molecules which contain two or more atoms bonded together, as long as the atoms are the same.
When iodine crystals are heated, they "sublime" (turn directly to a gas) to give purple vapors composed of diatomic molecules. The liquid phase, which also contains diatomic molecules, only forms under higher than atmospheric pressure. All the phases are the element iodine, because they contain only I atoms.
Other essential minerals are referred to as "elements", but are actually either toxic or useless to our body as elements. Foods must contain nutrients in chemical compounds that are easily digested and absorbed in our bodies in order for them to be nutritious. For example, the element phosphorus may have several forms. One, P4, is very toxic and actually burns when exposed to air, making a glow that's responsible for its name.
The nutrient form of phosporus is illustrated by mineral phosphates, like Ca3(PO4)2, which contains 3 calcium atoms (we will see later, they're in the form of "ions" each with a 2+ charge, Ca2+) and 2 "phosphate ions", each made of 1 phosphorus atom bonded to 4 oxygen atoms, and having an overall 3- charge. Phosphorus is also supplied in biomolecules found in meats and vegetables.
An "Elemental diet" is a solution of nutrients that can be administered intravenously (or with a gastric feeding tube) for people with digestive disorders, like Crohn's disease or colitis. There are no elements in an elemental diet, but the simplest chemical compounds that can provide complete (or near complete) nutrition. A typical elemental diet shows us what is required to maintain our bodies.  We require ounces to pounds of macronutrients daily, but typically less than 5 g (.2 oz) of micronutrients.
- Macronutrients (needed for energy and construction of body parts)
- Carbohydrates: Corn Syrup Solids, Mono and Diglycerides, Esters of Mono and Diglycerides
- Essential lipids:Fractionated Coconut Oil, Canola Oil, High Oleic Safflower Oil,
- Amino Acids: (L-Glutamine), L-Isoleucine, L-Leucine, L-Lysine-L-Aspartate, N-Acetyl-L-Methionine, L-Phenylalanine, L-Threonine, (L-Proline), L-Tryptophan, (Glycine), L-Histidine, L-Arginine, L-Valine, (L-Alanine), (L-Serine), (L-Tyrosine), (L-Cystine), (Taurine, a sulfonic acid).
- Micronutrients (used mostly in regulators of body processes)
- Minerals: Tripotassium Citrate, Tricalcium Phosphate, Dicalcium Phosphate, Sodium Chloride, Magnesium Acetate, Ferrous Sulfate, Zinc Sulfate, Manganese Sulfate, Cupric Sulfate, Potassium Iodide, Chromium Chloride, Sodium Molybdate, Sodium Selenite, (missing: F, V, B, Sn, Ni).
- Vitamins: Choline Bitartrate (B), (M-Inositol), Niacinamide (B3), Calcium-D-Pantothenate (B6), Thiamine Chloride Hydrochloride (B1), Pyridoxine Hydrochloride (B6), Riboflavin (B2), Folic Acid (B9), Cyanocobalamin (B12), D-Biotin (D7), Vitamin D3, L-Ascorbic Acid (C), DL-Alpha Tocopherol Acetate (E), Vitamin A Acetate, Phylloquinone (K1).
- Nutritional Supplement: L-Carnitine (normally synthesized from amino acids).
- Emulsifier, thickeners: Diacetyl Tartaric Acid, Propylene Glycol Alginate.
The ratio of chemical elements in our bodies is sometimes presented as a "formula for a human being", which does not represent any actual chemical compound, but just tells us the relative numbers of atoms:
H375,000,000O132 000 000C85 700 000N6 430 000Ca1 500 000P1 020 000S206 000Na183 000 K177 000Cl127 000Mg40 000Si38 600Fe2 680Zn2 110Cu76I14Mn13 F13Cr7Se4Mo3Co1
So for just 1 cobalt (Co) atom, we need 2 680 iron atoms, 1 500 000 calcium (Ca) atoms, etc. Clearly, there's a lot that chemistry can tell us about nutrition. But how do we know what is an "element" and what is a "compound", and what compounds provide the elements we need to maintain our bodies?
How Do We Know What Substances Contain Essential Elements?
The early greek philosophers (Empedocles, Lucretius and Democritus) proposed that everything was made of atoms, but had no way of providing evidence for the claim. Evidence that each chemical element is composed of one kind of atom (that is unchanged during chemical reactions) finally developed between 1750 and 1850. Looking at the pictures of potassium iodide (KI) and iodine (I2) above, will help to imagine how implausible it must have seemed that they share a common iodine atom.
Evidence for unchanging atoms as the components of elements came from weight measurements. Joseph Priestley and Antoine Lavoisier finally correctly interpreted the loss of weight when some substances burn (wood or sugar) and the gain in weight of others, by recognizing the fact that the mass of atoms in gases had been neglected. Lavoisier showed that mercury (Hg) gains weight because it combines with oxygen molecules from air to make solid mercuric oxide: 2 Hg + O2 → 2 HgO. But wood loses weight because it is converted to gaseous molecules of carbon dioxide and water of equal mass. The combustion reaction is similar to the combusion of the sugar, glucose, which the basis for the metabolism of carbohydrates in our bodies to provide energy:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
Earlier, van Helmont had failed to recognize that incorporation of carbon dioxide gas contributed the most to the weight gain of trees; he thought it was the water, because the soil showed virtually no change in mass. Nonetheless, he showed committment to the idea of concervation of mass, that no mass should be lost or gained during a chemical change. The equation for photosynthesis is just the reverse of the combustion equation above,
6 CO2 + 6 H2O → C6H12O6 + 6 O2
carbon dioxide + water + light energy → carbohydrate + oxygen
so we could say that trees are mostly CO2, and that when they burn, they release the energy that they had absorbed from the sun while growing:
As Lavoisier continued his experiments with oxygen, he noticed something else. Although oxygen combined with many other substances, it never behaved as though it were itself a combination of other substances. Lavoisier was able to decompose the red calx into mercury and oxygen, but he could find no way to break down oxygen into two or more new substances. Because of this he suggested that oxygen must be an element—an ultimately simple substance which could not be decomposed by chemical changes.
This was the fundamental discovery that allows us to identify tricalcium phosphate as a good source of "phosphorus" or potassium iodide as a good source of "iodine".
John Dalton (1766 to 1844) was a generation younger than Lavoisier and different from him in almost every respect. Dalton came from a working class family and only attended elementary school. Apart from this, he was entirely self-taught. Even after he became famous, he never aspired beyond a modest bachelor’s existence in which he supported himself by teaching mathematics to private pupils. Dalton made many contributions to science, and he seems not to have realized that his atomic theory was the most important of them. In his “New System of Chemical Philosophy” published in 1808, only the last seven pages out of a total of 168 are devoted to it!
The postulates of the atomic theory are given in the following table. The first is no advance on the ancient Greek philosopher Democritus who had theorized almost 2000 years earlier that matter consists of very small particles.
The Postulates of Dalton's Atomic Theory
1 All matter is composed of a very large number of very small particles called atoms.
2 For a given element, all atoms are identical in all respects. In particular all atoms of the same element have the same constant mass, while atoms of different elements have different masses.
3 The atoms are the units of chemical changes. Chemical reactions involve the combination, separation, or rearrangement of atoms, but atoms are neither created, destroyed, divided into parts, or converted into atoms of any other kind.
4 Atoms combine to form molecules in fixed ratios of small whole numbers.
The second postulate, however, shows the mark of an original genius; here Dalton links the idea of atom to the idea of element. Lavoisier’s criterion for an element had been essentially a macroscopic, experimental one. If a substance could not be decomposed chemically, then it was probably an element. By contrast, Dalton defines an element in theoretical, microscopic terms. An element is an element because all its atoms are the same. Different elements have different atoms. There are just as many different kinds of elements as there are different kinds of atoms.
Now look back a moment to the physical states of mercury, where microscopic pictures of solid, liquid, and gaseous mercury were given. Applying Dalton’s second postulate to this figure, you can immediately conclude that mercury is an element, because only one kind of atom appears.
Names, Chemical Symbols, and Atomic Weights of the Element
The chemical symbol for an element (or an atom of that element) is a one- or two-letter abbreviation of its name. Usually, but not always, the first two letters are used. To complicate matters further, chemical symbols are sometimes derived from a language other than English. For example the symbol for Hg for mercury comes from the first and seventh letters of the element’s Latin name, hydrargyrum. The table also includes atomic weights, which were used by early chemists to demonstrate the law of conservation of mass.
|Name||Symbol||Atomic Number||Atomic Weight||Name||Symbol||Atomic Number||Atomic Weight|
- ↑ Driskell, J.A. "Sports Nutrition", CRC Press, Boca Raton, FL,2000, p. 85
- ↑ http://www.chymist.com/iron.pdf
- ↑ http://www.neocate.com/aaa_neocate/694-neocate-junior-ingredients.html
- ↑ Sterner, R.W. and J.J. Elser, "Ecological Stoichiometry: The biolgy of elements from Molecules to Biosphere",Princeton University Press, Princeton, NJ, 2002, p. 3
- ↑ http://en.wikipedia.org/wiki/Van_Helmont