Bodily structures such as glands, hollow organs, and neurons "communicate" using chemical messages. Chemicals may interact with each other, enter into cells and alter physiology.









Chemistry is a major branch of science. It is important that anatomy and physiology students have an understanding of basic chemistry concepts.



Element


An element is a substance that cannot be broken down to a simpler substance and is the primary constituent of matter.


The known elements are described and organized in the Periodic Table of Elements


98.5% of the elements in the human body include:


Hydrogen (H)

Calcium (Ca)

Carbon (C)

Nitrogen (N)

Oxygen (O)

Phosphorous (P)


Atom


The basic unit of an element is the atom. Elements are made of many many same atoms.


Atoms consist of two major regions--the nucleus and the electron cloud.


The nucleus contains positive electromagnetic charged particles called protons and neutral (no charge) neutrons.


Surrounding the nucleus is the electron cloud which contains negative electromagnetic charged particles known as electrons


The number of protons and electrons in atoms is always equal. Therefore, atoms are electrically neutral.


The number of protons define the atom and therefore the element. For instance, the element hydrogen is exclusively composed of atoms with one proton.


The weight (mass) of an atom is determined by the number of protons and neutrons in the nucleus. The mass of electrons is so small that they do not significantly add to the weight of atom.




Electromagnetic attractive forces between the positively charged protons and negatively charged electrons maintain electrons around the atomic nucleus



Electrons


Electrons exist around the nucleus in energy levels defined by their proximity to the nucleus.


Each energy level may hold a maximum number of electrons.


The first energy level is closest to the nucleus and may hold a maximum of two (2) electrons.


The second energy level may hold a maximum of eight (8) electrons.


The third energy level may hold a maximum of 18 electrons.


More energy levels may hold successively more electrons.


In biochemistry, given the number of protons in over 98% of the body's elements, most electrons will be maintained within three energy levels.


Electrons furthest away from the nucleus exist in an energy level labeled as the valence energy level.


Valence energy level electrons have the most kinetic energy because they are furthest away from the positive electromagnetic attractive force.


When the atoms of elements chemically interact to form new substances, the interaction is always between the valence energy level electrons.








Elements on a periodic table may present with varying nomenclature. The nomenclature typically provides values that indicate the number of protons, neutrons, and electrons in the elements' atoms.



Typical Atomic Nomenclature


Elements are identified by one or two letter abbreviations. The first letter is always uppercase and if there is a second letter it is always lowercase.


The left superscripted number as pictured to the left is the atomic number. The atomic number represents the number of protons in the atomic nucleus.


The left subscripted number represents the atomic mass number. The atomic mass number represents the sum of the protons and neutrons in the nucleus.


The center subscripted number represents the atomic weight. The atomic weight is always represented as a decimal several places out.


The atomic weight is the weighted average of all versions of a particular atom. Though the number of protons is static, An atom may have versions with a differing number of neutrons. An atom with a "non-standard" number of neutrons is called an isotope.