The Periodic Table of the Elements
Created | Updated Jul 25, 2013
The periodic table of the elements is a nicely organised collection of data about the types of existing atoms (AKA: elements). More detailed information about the table is found in this entry right after the table itself. Just for a quick start: using the table is really quite simple. To save horizontal space this version of the table is subdivided into three parts: The main group elements, the transition metals and the rare earths. One can use the group, period and atomic numbers to reconstruct the complete table (it should work like a map). The syntax of the table is as follows:
An asterisk (*) beside the atomic weight indicates that the element is radioactive. The names and the relating symbols are included in a separate table. Further down the entry (after the table part) there are some chapters dedicated to the table itself and to more detailed information about its usage.
The Periodic Table of the Elements
Element name table
More Detailed Information
The periodic table of the elements is a work of generations of scientists (see: History of the Periodic Table), it is not complete1 and it is not in its final layout2. The artificial elements with the atomic number above 105 only exist as traces, they are so instable that only few atoms of these elements have ever been synthesized. The more 'stable' part of the periodic table is widely used in research labs all over the world.
Other Properties of the Elements
Few elements are non-metals. They are: Hydrogen (H), the entire group 18 ('Noble Gases'), Group 17 excluding At, Group 16 excluding Po and Te, Group 15 N and P, As is a semi-metal, Group 14 C, Si is a semi-metal and from Group 13 only B.
Few elements are gaseous at normal conditions (298 K, 1 atm): H (H2), N (N2),O (O2),F (F2),Cl (Cl2) and the Noble Gases. Only two elements are liquid at normal conditions: Hg and Br.
All elements have a variety of different isotopes which are elements with the same nuclear charge but a different amount of neutrons. The properties of different isotopes of the same element vary only very slightly from a chemical point of view. Elements that only have one natural isotope are: Be, F, Na, Al, P, Sc, Mn, Co, As, Y, Nb, Rh, I, Cs, Pr, Pm, Tb, Ho, Tm, Au and Bi.
The measurement unit of the atomic weight is the amu (atomic mass unit). 1 amu corresponds to 1/12 the mass of the 12C isotope (it is sort of an average between the mass of protons and neutrons).
How to Use the Periodic Table of Elements
The table is most commonly used to look up the atomic weight of the elements. Those are used to calculate the molar mass of any compound. The molar mass of a compound is the mass in grammes of 6.022 x 1023 units of the compound (normally molecules). The number 6.022 x 1023 is also called one mole or the Avogadro3 number or more rarely the Lochschmidt number4.
Example: (To illustrate the usage of moles, atomic weights and the periodic table.) For any reason a chemist needs one mole of potassium permanganate (KMnO4). She looks at the formula and calculates the weight of one mole of potassium (by checking the periodic table), one mole of manganese and four moles of oxygen (four because there are four oxygens in one unit of the permanganate). She adds the numbers and finds that she will need 158.04 grammes of the potassium permanganate (which is available as a violet, rather dangerous powder). Weighing a powder is more effective and can be done faster than counting all 6.022 x 1023 molecules5
The second most common use of the periodic table is as laboratory-deco. The periodic table is often found impressed on mouse-pads, t-shirts and posters (in all kinds of design ranging from serious to colourful). Something must be wrong if a chemistry office or lab is not decorated with a periodic table somewhere.
Other usages of the periodic table require some experience in chemistry. The periodic table is organised in a more complex way than it appears on first sight. The elements are not just ordered according to their atomic number (or weight). The position of an element in the table will tell the scientist something about its chemistry. This is so, because the elements are also arranged according to their electronic configuration. (See also: electronic configuration)
How to Use the Periodic Table of the Elements (Advanced)
There are two fundamental trends that go along with the electronic configuration, and the position of the element in the table.
The electronegativity6 increases from left to right in the periodic table, and decreases with the period (excluding the noble gases: they do not have an electronegativity).
The atomic radius decreases with the group number (from left to right), and increases with the period (top-down).
These properties allow an evaluation of the shape and consistency of the electron shells of a certain element. From this, it is possible to estimate the acidity of the hydrides, the solubility of certain compounds in water, the reactivity with other compounds.
Example: What can be predicted for NaBr (sodium bromide) just from the periodic table? Sodium is not very electronegative (it is on the very left side of the table), it will lose his electron for any species which desires to own it more dearly (i.e. for anything with a higher electronegativity), like the bromine atom (on the right side of the table). The sodium loses one electron and will become positively charged, and the bromine atom receives a negative charge. Charged elements (also called ions) are known to be well soluble in water.7 Remark: This explanation is descriptive, it helps to get the picture. One must bear in mind, though, that the real processes taking place in a solution are overwhelmingly more complex and exhaustingly difficult to explain.
Other stuff worth knowing
As mentioned before, the periodic table is a collection of element-data arranged according to their weight, and to some of their properties. From this arrangement, the groups have received names which are still in use today. The most well known group-name is probably the halogens (or rather unadorned: Group 17). Before starting with more detailed information on each group, let there be the remark that hydrogen is a big exception, it doesn't fit into any group. And here are the group-names:Alkali metals - Group 1 (excluding hydrogen): The reaction of these elements with water result in an alkaline solution, hence the name of the group.
Alkaline-earth metals - Group 2: The reaction with water will also lead to an alkaline solution. The addition of 'earth' to the denomination of this group is due to the findings of minerals containing these elements in earth.
Triels - Group 13 (or 'boron-group'): This is a synthetic name originating from the time when group 13 was known as group 3 (tri from the greek version of 'three', and els being a new short form for 'element')
Tetrels - Group 14 (or 'carbon-group'): Same thing happened here. (From tetra which is greek for 'four')
Pentels - Group 15 (or 'nitrogen-group'):Same thing with penta (greek; meaning 'five')
Chalcogens - Group 16: Elements of this group form ores. (chalcos is greek for 'ore' and gennan means 'to form', 'to generate' - like in 'genesis')
Halogens - Group 17: Elements of this group form salts. (halos the greek word for 'salt' and gennan 'to generate')
Noble Gases - Group 18 (or 'inert gases'): Elements of this group do not react. And 'noble' sounds better than 'snob'.
Links. The periodic table of the elements in the net.Webelements.com (very graphic)
IUPAC Homepage (very official)
The Pictorial Periodic Table (very complete)