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(updated 12/23/05)        Return to Science Standards

Approximate percentage of major elements in the human body (shown by weight).

The Periodic Table of Elements below is designed to indicate the relative amounts of certain elements by the height of each column.  The abundance of some elements , such as Silicon and Aluminum, is quite different from the amounts of these elements found in living organisms.  

The table is arranged in Groups having similar chemical behavior (vertical columns), and in  7 Horizontal Rows that indicate the seven energy levels of electrons surrounding the nucleus of each atom.  

Metals occur in the left 2/3 of the table, nonmetals are primarily in the upper right portion, and metalloids (having some properties of each) are generally in a diagonal line from #5 & 6 (boron and carbon) down and towards the right, including, but not limited to aluminum, silicon, phosphorus, and # 32, 33, 51, 52, 84, &  85. 

The Atomic Number represents the number of Protons (+ electrical charges) in each atom, while the Mass Number (see Periodic Table listed for Inorganic Chemistry lab) represents the number of protons and neutrons in an atom.  The number of electrons (- electrical charges) is equal to the number of protons.  See figures below the Periodic Table for atomic structure.  When an element has 8 electrons in its outer energy level (Group 8A), it becomes stable and does not react with other atoms (Helium is an exception to this octet rule, since it can only contain two electrons).  Group 8 is referred to as Inert or Noble Gases.  Helium is used in balloons since it is light weight and non-reactive. Numbers below the Group Numbers refer to the Atomic Number of the top element(s) of each group in the table below.


1A      2A                                                                                        3A      4A     5A   6A    7A     8A

                     3B    4B     5B   6B   7B          8B            1B    2B

  1        4        21    22      23    24    25   26     27     28   29    30     5        6       7      8        9       2                    


Know the parts of an atom and their electric charges. Also, be able to illustrate the structure of any element found in the body based upon the Atomic Number, Mass Number, and location on the Periodic Table of Elements.  For example:

Labeled parts of an atom of lithium (Element #3).

Distribution of electrons in hydrogen, helium, and lithium atoms. A 'strong force' (gluon) holds atomic nuclei together, while a 'weak force' (boson), which is one million times weaker, governs radioactive decay. Electromagnetic forces (photons), which are 1000 times weaker than the strong force, bind molecules together. See information below on Electronegativity. Compared to these forces, gravity is 10-39 weaker.

Table listing structural characteristics of the first 12 elements in the Periodic Table.

Be able to determine the types of chemical bonds formed by combining different elements.  Although slightly inaccurate, use the following figures as a guide. If the difference in electronegativity (EN) between two atoms is 0 < 0.4, these atoms do not carry a strong electrical charge, and form nonpolar covalent bonds.  Example: methane gas, CH4; EN of Carbon = 2.5; EN of Hydrogen = 2.1.  2.5 - 2.1 = 0.4    If the difference in EN is between 0.5 < 1.7, the bonds are generally polar covalent. Examples H20, and HCl.  If the difference in EN is from 1.8<3.3, the bonds are ionic. Examples NaCl  (3.0 - 0.9 = 2.1); FrF (EN of Fluorine = 4.0; EN of Francium = 0.7) (4.0 - 0.7 = 3.3).  The general rule is that the EN increases as we go up and to the right on the Periodic Table. The Inert (Noble) gases in Group VIII have no EN value. For a view of all electronegativity values, and a printable periodic table, see:

Although the bonds within water are polar covalent, a different, weaker attraction between water molecules, a hydrogen bond, exists. These bonds account for many of the properties and biological functions of water.

Ionic bonding of Sodium and Chlorine. The difference in Electronegativity values is 2.1 (3.0 for Cl minus 0.9 for Na). The difference is between 1.8 and 3.3, therefore producing an ionic bond. This is why saltwater conducts electricity so easily, and is one reason why our body conducts electricity.

Substances that carry electric charges are known as electrolytes. Many of these are important in life, in that they allow energy to flow through the body, and account in part for nerve and brain function, muscle contractions, and many other processes (see Table 2.6 below).

pH is a measure of the Hydrogen ion (H+) concentration.

pH concentrations increase by logarithmic units (each step in pH increases or decreases concentrations by 10X). Thus, a substance with a pH of 3 is 1000X more acidic than one with a pH of 6, while the substance with a pH of 6 is 1000X more basic (alkaline) than that with a pH of 3.

Ignore the chapter references listed below; they do not pertain to your textbook. Of utmost importance among electrolytes, four cations (+ ions) Na+, Mg++, K+, & Ca++ (atomic numbers 11, 12, 19, & 20, respectively), and one anion, Cl- (Atomic # 17), must remain in proper balance. Also involved are bicarbonates (HCO3-), phosphates, H+ ions, and others shown below, which help to maintain the pH balance (7.35-7.45) and electrical flow of energy, which allow nerves and muscles to function, so that we can stay alive. If any one of the major cations or anions get out of balance, then all may get out of balance, thus disrupting many life processes. These are especially important to monitor in infants and the elderly, since rapid change can be life-threatening or fatal in a short period of time.

Probably the most important chemical formula for A&P students to remember is the following. 70% of the carbon dioxide carried in our bloodstream is in the form of sodium bicarbonate (baking soda). When CO2 dissolves in hater, it enters red blood cells (rbc) and reacts with an enzyme, carbonic anhydrase, and changes into carbonic acid. This acid then dissociates into bicarbonate ions and hydrogen ions. The hydrogen combines with hemoglobin (Hb), which makes up 1/3 of the volume of the rbc, to form acid hemoglobin (HbH+). The bicarbonate ions combine with Na+ to form the sodium bicarbonate. Some chloride ions (Cl-) enter the rbcs and combine with K+ ions which remain in the cells. Whenever this blood enters into the lungs, all of these reactions are reversed, and the CO2 diffuses out of the blood stream and into the alveoli of the lungs, where it is exhaled. Hemoglobin functions as a buffer in the blood (in addition to transporting 97% of the oxygen) by forming the weak acid hemoglobin. Buffers prevent the pH from changing drastically, which could be fatal.