The Periodic Table
Grouping Elements by Atomic Structure
The foundation for understanding the Periodic Table is our tutorial on Atomic Structure. In this tutorial we built the first 20 elements from the simplest element Hydrogen (H) by adding protons and electrons.
This provides us with a good understanding of the specific and unique Atomic Structure of the atoms of each element. These elements can be grouped by Atomic Structure as shown in the picture above.
In the tables above we list the 20 elements we have constructed in order of increasing Atomic Number. This means of course in the order of increasing number of protons.
We have also included the Shells (energy levels for the orbiting electrons) labeled by number and color coded to match our atom structure diagrams (for details see our tutorial on Atomic Structure). In addition we have listed the Atomic Mass and a column in which we calculated the number of neutrons.
This grouping of elements by Atomic Structure is the basis for the Periodic Table. Elements are organized into Rows or Periods based on their Outer Shell Number - 1,2,3...
The elements are further organized into Columns or Groups based on the number of electrons in their Outer Shells. The Columns are numbered with Roman Numerals into Groups I,II,III...
If we continue this grouping for the entire 111 known elements and arrange the elements by rows and columns, the resulting table is the Periodic Table
Organization of the Periodic Table
If we group the elements by rows with each row number representing the Outer Shell number of the element the result is seven rows as shown in the picture above.
If we further group into columns by the number of electrons in the Outer Shell and assign each column a Roman Numeral we see from the above table that we have two groups of columns - an A and a B group.
The B group of columns is referred to as the Transition Metals and will be explained in detail later, so for now let's just focus on the A group of columns.
The A group of columns (IA through VIIIA) makes up the first two and the last six columns of the Periodic Table. The elements grouped into the first two columns have one and two electrons, respectively, in their Outer Shell. The elements grouped into the last six columns have 3,4,5,6,7 and 8 electrons, respectively, in their Outer Shell.
As we shall discuss in more detail later, the importance of the number of electrons in the Outer Shell of an electron is based on the fact that all elements want either an empty (no electrons) or a full (8 electrons) outer shell. The chemical reactivity of an element is based on gaining, loosing or sharing electrons in its Outer Shell to get to "full" or "empty".
As we discussed above, the common elements (Groups 1A through VIIIA) reside in the first two and last six columns of the Periodic Table. The electrons for these elements fill the lower energy orbitals - s (spherical-shaped) and p (dumbell-shaped) orbitals - of their Outer Shells as shown in the picture above.
The less common elements, referred to as the Transition Metals and the Rare Earth Elements, reside in Groups IB through VIIIB. These electrons for these elements fill the higher energy level orbitals - d (X-shaped) and f (complex-shape) orbitals - of their Outer Shells as shown in the picture above.
The picture above names the elements according to their physical and chemical properties. Metals (primarily Groups IA and IIA) tend to want to loose electrons to achieve an empty Outer Shell, while Non-Metals (Groups IIIA through VIA) tend to want to share electrons to achieve a full Outer Shell.
Halogens (Group VIIA) want to gain electrons to achieve a full Outer Shell. Inert Elements (Group VIIIA) already have a full Outer Shell, do not readily react and therefore are referred to as Inert.
The Transition Metals and Rare Earth Elements in Groups IB through VIIIB gain and loose electrons from the higher energy d and f orbitals.
Valences - Basis for Reactivity
When elements loose, gain or share electrons they do so in a manner consistent with what is necessary to achieve either a full or empty Outer Shell. The number of electrons that must be lost, gained or shared to achieve the stability of the empty or full outer shell is referred to as the Valence of an Element. The table above shows the Valence of the various groups of Elements in the Periodic Table.
When an element looses an electron(s) the Valence is positive due to the loss of the negative charge of the electron(s). When an element gains an electron(s) the Valence is negative due to the gain in negative charge of the gained electron(s).
When an element shares an electron(s) the Valence can be either positive or negative depending on whether the element is a "donator" of electrons (positive Valence) or a "receiver" of electrons (negative Valence). The table above shows the Valence of the various groups of Elements.
The Periodic Table of the Elements
We are now ready to "fill in the blanks" of the Periodic Table which is shown with the element names in the picture above. The Symbol for each element is given in center of each cell along with the Atomic Number (above the Symbol) and the Atomic Mass (below the Symbol). A complete listing of all the known elements is given in the two pictures below.
You now have and understanding of the "Chemical Code" of the Periodic Table. Remember the chemical reactivity of an element is determined by the number of electrons in its Outer Shell.
The lowest energy state for an element is either a full Outer Shell or an empty Outer Shell. An empty Outer Shell is stable because it has a full "Inner Shell". The Valence of an element is the number of electrons the element must loose, gain or share to attain a full or empty Outer Shell.
The Alkali Metals of Group IA need to loose one electron to achieve an empty Outer Shell and so have a Valance of +1. The Alkaline Earth Metals of Group IIA need to loose two electrons to achieve an empty Outer Shell and so have a Valence of +2.
The Halogens of Group VIIA need to gain one electron to achieve a full Outer Shell and so have a Valence of -1. The Inert Elements of Group VIIIA already have a full Outer Shell and therefore do not need to gain or to loose electrons and therefore are inert (do not react).
The Non-Metals or Other Metals of Groups IIIA through VIIIA tend to want to share 5 to 2 electrons, respectively, to gain a full or empty Outer Shell. So, these elements can have a Valence of 2 to 5 and can be either positive (if they are electron donators) or negative (if they are electron receivers).
You now have the knowledge to understand the "Chemical Code" of the Periodic Table and can use it to "de-code" how any element will react given its position within the Periodic Table.
The purpose of this section and our section on Atomic Structure is to give you a step-by-step fundamental understanding of how all the elements are organized by atomic structure into the Periodic Table. The Internet has literally hundreds of Periodic Tables. The very best we have found totally interactive and can be found at found at Ptable.com
Click here for our tutorial on Atomic Structure
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