RLO Transcript: Elements that make up the Human Body
This is a transcript of the Reusable Learning Object (RLO) entitled "Elements that make up the Human Body", online at:

http://www.nottingham.ac.uk/nursing/sonet/rlos/science/body_elements/
The Table
The known universe is made up of about 100 different types of elements, each with differing chemical and physical properties.  These differing properties are partly related to the structure of the atoms that make up these elements.   Chemists have devised a table known as the periodic table in which to record all of the elements together based on their atomic structures.  

You can see a copy of this table here. The table allows us to identify relationships and similarities between the different elements.  

The human body is made up almost entirely of 13 elements, and by identifying where these sit within the table we can discern certain things about the nature of the elements and how they react within the body.

Each element is represented by its internationally agreed short-hand, for example H for  hydrogen,  Mg for magnesium,  Cl for chlorine and Na for sodium.
Organisation 
The elements are not just placed randomly, but are in a highly specific pattern that relates to their physical and chemical properties.

From left to right, the rows of the table contain elements with increasing numbers of protons, shown by the atomic number found at the top left hand side of the symbol  and with increasing mass, shown by the atomic mass number shown in the bottom left hand corner of the symbol

The columns of the table contain elements with similar chemical properties to one another. This is partly de to the fact that atoms in the same column or group have a similar arrangement of electrons in their outermost shells and it is this arrangement of electrons in the outer most shell that has a major influence on the chemical properties of the element as the atoms act to fill these outer shells
Groups
Here are a family of metal elements, including lithium, sodium, potassium,  rubidium, caesium and francium.  They all have only have one electron in the outermost portion of their atoms.   This single electron is easily removed, and this makes the elements in this group very reactive as they can easily lose this electron to another atom or molecule that they encounter.

Here on the other side of the table is a column containing the group of elements known as the halogens.  This group includes familiar elements such as fluorine, chlorine and iodine.
The atoms of this group of elements all lack only one electron from their outer shells.  Here again, they can easily acquire one electron from another atom making these elements highly reactive

The groups in between these columns have atoms with intermediate numbers of electrons in their outer shells making them more or less reactive

The group on the end of the chart here contains elements whose atoms already have complete outer shells.  These are known as the inert gases, and as their names suggest, they are generally non-reactive.
Metals and non-metals
We can determine a couple of other major groupings on the periodic table. Elements on the right hand side of the table are known as the non-metals, they don’t conduct electricity

Elements on the left side are the metals, they do conduct electricity.

There is no clear cut division between the two, and a few elements show properties of both metals and non metals.
Body elements
As we have already discussed, the human body is almost entirely composed of 13 elements. Carbon, hydrogen, oxygen and nitrogen make up 96% of our body’s mass.

The other 4% of body weight is composed almost entirely of  sodium, potassium, magnesium, calcium, iron, phosphorus, sulphur, chlorine and Iodine .

You can see where these elements sit on the table and thus can guess at some of their chemical properties.  Click on the highlighted elements to see information about the element and its role in the human body. 
Glossary
•	Atom: an electrically-neutral combination of electrons, protons and neutrons, the "smallest unit of an element to retain all the chemical properties of that element" (Wikipedia). 
•	Atomic Number: the number of protons in an atom.
•	Atomic Mass: the number of protons plus the number of neutrons in an atom. 
•	Compound : a chemical substance formed from two or more elements.
•	Electron: an almost weightless particle carrying a negative charge. 
•	Element: a substance that can't be reduced to a simpler substance by chemical means. 
•	Molecule: a coherent particle comprising two or more atoms, "the smallest particle of a pure chemical substance that still retains its chemical composition and properties" (Wikipedia). 
•	Neutron: a particle with no electrical charge with a mass nearly equal to a proton. 
•	Proton: a particle with a positive charge with a mass nearly equal to a neutron.