This is the most unique and practical use of the periodic table there is with respect to electrons (e-)! The characteristics of atoms (elements) is that they bond together {(forming molecules, etc.),.(or with respect to Noble Gases may resist bonding altogether)}.

The periodic table as a chart is useful for looking up and comparing reference values like atomic mass, the number of protons that an element has ....(and again IT IS USELESS FOR DETERMINING THE NUMER OF NEUTRONS AN ELEMENTS HAS! see... Chart of the Nuclides. etc.

So, "Yes! You Heard Me!" THE PERIODIC TABLE IS NOT MADE FOR TEACHING CHEMISTRY! ("It is used as a reference table, to look up values of physical properties. {(Electronegativity values and oxidation states are what are needed on a periodic table to 'teach chemistry') (So have you noticed the 'periodic table' on the inside of the Introductory Chemistry testbooks lacks these, the only two things that can tell you 'ANYTHING' about 'How the atom will react'?}

See why I say, "It's not that chemistry is hard, IT'S THE WAY THEY TEACH IT! (So to have someone that doesn't 'know' it try to teach it to a class by using a textbook is STUPID!!!!!!!

(So one more time! the 'Chart of the Nuclides' is what's needed to explain the 'atoms' (or 'elements') itself (# of protons and neutrons in the nucleus...)

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Now the e-'s! 

I rememeber asking a university professor, "how can students learn oxidation states?" He said, "look at the periodic table".... and he opened the textbook cover... I said, "What does that tell you about the three different oxidation states for sulfur...?" He just gave me a dumb look.

See sulfur can be like oxygen and bond with two hydrogens so like H2O (so it's H2S ("H two S", is common, in rotton eggs, 'Hydrogen Sulfide' {so yes water is technically hydrogen oxide'}

But now sulfur has more protons (and neutrons) than the tinier oxygen atom does...so has more space for electrons around it to bond... so sulfur can have' TWO Bonds' (the hydrogen sulfide (H2S), I just mentioned...), or it can have '4 bonds (in S(F)4, or S(Cl)4, or two 'double bonded' oxygen atoms in 'SO2......

Now the Kicker! Sulfur can also have SIX BONDS!!!!! SF6 (that is six fluorines bonded to one sulfur atom). Also, see the Sulfuric Acid (or 'Sulfate anion's 'oxy' acid series) molecules. This is a significant biological molecule and is known to determine many a countries economy by the use is feeding people as fertilizer for crops...)

Again, no fancy pictures to this point you have to be able to pick up a pen and draw what you're explaining...You need to be able to draw electron pairs around an atom to describe the chemistry of the element...It's NOT THAT HARD!

Again after the first pair of e-'s, we find there are shells of eight (8e-'s, "The 'Octet'), so if atoms are bound by pairs of electrons that's 'FOUR PAIRS', so to make Carbon resemble Neon, with a full 'Octet', four more electrons, resulting in four bonds that are common for carbon (in fact, "So Many Bonds..., and chains can form such a wide variety of molecules, that 'Organic Chemistry' is a field that just studies carbon compounds...

*********************************New to here mas manana or so... c10FEB2009RJSchroeder

So knowing why ther eare four or six and not five or three is where the oxidation states come into play when there is a chemical reaction there are electrons changing places the nucleus stays the same (that's the chemical reaction versus the nuclear reaction which is covered in physics more than chemistry nowadays...

So if you want to learn what's not being taught this is the Periodic Table for you, "The Lewis Octet Valence e-DOT Folding Periodic Table of the Elements".

There is so much more, this is a year of 'College Chemistry" on one sheet of paper and so much fun and colorful history to be shared among all grade levels.

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)