The Periodic Table of the Elements-A TWO STAR PAGE-Goal is to understand and explain this page using your own drawings and a generic periodic table)

Elements are atoms. The number of protons ONLY is what determines the identity of an element, such that there can be differing numbers of neutrons in the nucleus for a given element. Thus an element is considered to be the sample that you would find in nature (or that was made for the larger "man-{and WOMAN!}-made" elements it may simply be one atom.

To understand this consider the atomic mass of sulfur from Louisiana that has differing isotope percentages than sulfur from Italy. {The ISOTOPE is the atom that has a certain number of neutrons -BUT REMEMBER THE NUMBER OF PROTONS HAS TO BE THE SAME, OR ELSE IT WOULD BE A DIFFERENT ELEMENT).

This is why the chart of the nuclides (isotopes) is important (and overlooked!) to understand the periodic table of the elements. All the periodic table of the elements does is list the elements in order of atomic number (the number of protons, ONLY!).

So let's take hydrogen, the simplest element with only one proton. Most of any sample of hydrogen will be that with just one proton in it's nucleus, but one in every 7000 may be the deuterium isotope (one proton with one neutron, sometimes called the "heavy hydrogen"). The even rarer is the tritium isotope, with two neutrons but still only one proton. With three types of atoms making up a sample of hydrogen it averages out that one mole of hydrogen doesn't weigh one gram, but rather the atomic mass turns out to be 1.00794 grams per mole.

The best example of this is for elements #52 (Tellurium) and #53 (Iodine)...you would think that iodine would weigh more than tellurium wouldn't you?! Since there are more heavier isotopes on average for a sample of tellurium whose atomic mass is 127.60 grams per mole while 126.90 is the atomic mass for the iodine, even though iodine has a higher atomic number the atomic mass is less...You can imagine the confusion when iodine was placed before tellurium in early periodic tables....

To master the periodic table however, you also need to consider the electrons for an atom...Remember that it is the # of protons that determines the element, such that there is confusion when protons are coming and going in water solutions and photosythesis. To the chemist, hydrogen means the proton WITH IT'S ELECTRON! you can't say that a hydrogen atom is taken away if it is only the proton without it's electron also (the neutrons aren't involved anymore).

This is a cause for confusion when bigger elements are involved because electron can come and go and you can call it an atom. For example if you pour sodium chloride, table salt, into a glass of water, the sodium is pulled into the solution after it has given up an electron to a chlorine atom. this is called ionization and is a key to how atoms bond and where an element is placed in the periodic table. So if a chlorine atom takes an electron from sodium when it dissolves in water, we still can call it a chlorine atom but it is technically called the chloride anion, which has a negative one charge. With 17 protons in any chlorine atom whether it has 18 neutrons or 20 neutrons it is still simply the chlorine atom, but since a neutral chlorine atom can only have a matching number of electrons (seventeen to match the #of protons) the single extra electron doesn't change the identity of the atom but it is enough to make chlorine change from being poisonous to being an essential element in humans (YES ONE ELECTRON EXTRA DOES THAT FOR CHLORINE!). Conversely the sodium atom with 11 electrons is explosive, but when it gives up an electron and gets a positive one charge (and thus dissolves in water) it also becomes an essential element! So in a way you can say that ONE ELECTRON MAKES LIFE POSSIBLE!!!!!!!!!!!!!!

The periodic table lines up elements in order of the # of protons (atomic number), but the key to the columns is the number of valence (outermost) electrons. To simplify things chemists picture electrons filling shells such that once a shell is filled we only become concerned with electrons outside the full shell. Consider the first two elements hydrogen and helium. With two electrons and the inertness of helium, it has a shell that is full and is stable. Hydrogen can have valences of no electrons, one electron, or two electrons. With the case of hydrogen with two electrons it is pictures as having a full shell (called the "NOBLE GAS ELECTRON CONFIGURATION").

After a pair of electrons, the next shell requires eight electrons (called an 'OCTET'). This element is neon, with atomic number 10, with two electrons in the first shell and the next shell of eight being full. With the shells full, this is what allows neon to be unreactive (and known as a "NOBLE GAS"). Thus a great example of valence electrons dictating an elements postion on the periodic table is the fluorine atom above the chlorine atom. Both of these elements have seven valence electrons outside their respective noble gas electron configurations. Fluorine is the most reactive atom needing one more electron to complete the octet outside the inner electron pair. This is where even with the nine protons (providing an electric charge of positive +9), the fluorine atom requires 10 electrons to be stable (so in water the fluorine anion, F- is how you would find it-resembling the noble gas electron configuration of neon)...Chlorine has 17 protons (and positive +17 electric charge) but would be stable with 18 electrons since two would fill the first helium shell, then eight to fill the neon shell, and with only seven for the next noble gas shell (resembling argon), an extra electron makes the chloride anion stable in water, Cl-, 18 electrons (2,8,8=2+8+8=18e-'s)

PERIODIC TABLE UPDATES 2003