Model 1. All of the elements on the periodic table can be found in nature as pure substances. An element is made of atoms, therefore a sample of the element calcium would be made of many calcium atoms. A compound is also a pure substance. A compound is made of molecules, therefore a sample of the pure compound water would be made of many water (i.e. H2O) molecules.
Table 1.1. Examples of various types of matter at room temperature (70°F/21°C)
|Item||Classification||Is it a Molecule?||Chemical Formula|
|Sodium chloride (i.e. table salt)||Compound||Yes||NaCl|
(i.e. table sugar)
|Monosodium glutamate (i.e. MSG)||Compound||Yes||NaC5H8O4N|
Molecules are formed from the bonding of two or more atoms. Most matter on earth, including food, is a mixture of different types of molecules. A molecule is the smallest, neutral (that is, without charge) unit of a substance formed by bonding two or more atoms together. Molecules and compounds are often used interchangeably to describe a substance. The simplest way of thinking about it is that a compound must contain at least two different elements and a molecule is anything that has more than one atom.
|Figure 1.1. The Periodic Table of the Elements lists all the known elements by increasing size (left to right and top to bottom)
All living things (animals, plants microbes, and smaller life forms) are made of atoms and molecules. How those molecules are organized, interact and react are the building blocks for life. Molecules are often divided into two categories, organic (those molecules containing carbon atoms) and inorganic molecules (everything else).
|Most food is a mixture of molecules. Consider the nutrition data for a medium orange in Figure 2.|
|Food molecules are typically classified in three main categories: Fat, Carbohydrate, and Protein.
Fat, Carbohydrate and Protein are large classes of molecules that contain many different specific examples. See Table 2.
|Cholesterol is a molecule; it has the molecular formula C27H46O.
|Vitamin A (C20H30O) and Vitamin C (C6H8O6) are both molecules.|
|For Sodium, Calcium and Iron – see model 2.|
|Figure 1.2. Nutrition Data for 1 medium orange|
1. Consider Table 1.1. How does the formula of an element differ from that of a compound? How can you distinguish elements from compounds based on their chemical formulas?
2. According to Table 1.1, oxygen exists as a molecule, but not a compound – why is this?
Table 1.2. Examples of food molecules from the major classes: fat, carbohydrate and protein.
|Type||Specific example||Molecular formula|
|Carbohydrate||Glucose (i.e. dextrose)||C6H12O6|
3. Using the Periodic Table of the Elements in Figure 1.1, list the elements found the items of Table 1.2. How can you tell what elements are present?
Model 2. Sodium, Calcium and Iron appear on nutrition data labels for all foods , and yet the pure elements sodium, calcium are indigestible by humans. In fact, the pure elements sodium and calcium are downright harmful! They will burn your skin and certainly your mouth if you try to consume them. The element iron is not harmful, but it is not very digestible. Sodium, calcium and iron are examples of metals. How then can most benefit from these metals in our food?
Table 1.3. Sodium, calcium and iron in food.
|Pure Element||As found in food||Food sources|
|Sodium (Na)||sodium chloride (i.e. table salt, NaCl), monosodium glutamate (i.e. MSG, NaC5H8O4N),
sodium bicarbonate (baking soda, NaHCO3),
sodium benzoate (NaC7H5O2)
|Milk, celery, bacon and condiments like Worcestershire sauce.|
|Calcium (Ca)||calcium citrate (Ca3C12H10O14)
calcium lactate (CaC6H10O6)
|Calcium supplements, cheese|
|Iron (Fe)||Heme (FeC34H32O4N4)
ferrous sulfate (FeSO4)
ferrous fumarate (FeC4H4O2)
|Meat, fortified infant cereal|
4. Compare the column Pure Element versus the column As found in food from Table 1.3. What can you conclude about the sodium, calcium and iron represented in the As found in food column.
Model 3. Sodium, calcium, iron and other metals found in food are most often consumed as part of ionic compounds. Ionic compounds are comprised of two halves: a cation (pronounced CAT-EYE-UN) and an anion (pronounced AN-EYE-UN). The cation carries positive charge, while the anion carries negative charge – together the charges balance each other and the overall compound is net neutral. Finally, an ion is different from an element. For example, the element sodium has a neutral charge, but the sodium ion does not.
Table 1.4. Examples of ionic compounds found in food.
|Ionic Compound||Molecular formula||Cation||Anion|
|calcium citrate||Ca3C12H10O14||3x Ca+2||2x [C6H5O7]-3|
In an ionic compound – for example, sodium chloride – the cation is always carrying a positive charge (Na+) and the anion is always carrying a negative charge (Cl-), but sometimes the ionic compound will be represented with cation and anion listed one after the other (e.g. NaCl) – without the charges explicitly shown. In the NaCl example, the combination of one positive charge and one negative charge creates the overall neutral compound (NaCl). While the charges on the sodium cation and chloride anion might not always be shown – they are always present. You should learn to recognize the pattern of naming that identifies an ionic compound like sodium chloride.
In addition, all but one of the anions in Table 1.4 is made of many atoms – and these ions are said to be polyatomic . In these cases, the charge is associated with one or more discreet atoms. For example, the anion fumarate is drawn in Figure 1.3.
Figure 1.3. The anion fumarate.
5. From Table 1.4, what can you tell about the pattern of naming ionic compounds? What comes first, what comes second?
6. Explain how calcium citrate in Table 1.4 is a net neutral ionic compound. Remember, the negative and positive charges must balance out in the final compound.
7. Using Figure 1.3 and Table 1.4, propose a molecular formula for calcium fumarate. Give a rationale for your answer.
8. While sodium chloride is what we know a “table salt”, all the other compounds in Table 1.4 are also examples of “salts”. What must be the basic requirements for a salt?
Putting it all together:
9. Find the molecular formula for the following compounds. Determine the types of atoms present in each substance using the Periodic Table. For each substance determine whether it is an element or a compound.
b. Sodium citrate
10. Are any of the compounds in the preceding problem an ionic compound? How can you tell? List the cation and anion.
Molecules are formed from the bonding of two or more atoms.
Most matter on earth, including food, is a mixture of different types of molecules.
� The nutrition data for 1 medium Florida orange was supplied by the United States Department of Agriculture Agricultural Research Service, National Nutrient Database for Standard Reference Release 27. The data is in the public domain.
� An omega-3 fatty acid found in green leaves and some seed oils.
� The primary fatty acid found in olive oil
� Alanine and glutamate are components of protein
� � HYPERLINK “http://www.nutrition.gov” ��www.nutrition.gov�
� MedlinePlus. Sodium in your diet.
� The word ferrous is derived from the latin word ferrum, which means iron
� Poly = many, atomic = atoms, as in elements.
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