By Ron B. Davis Jr., Georgetown University
The right side of the periodic table or the p-block is where all the types of elements come together. There are elements that range from brittle and toxic metals to semiconductors, from inert gases to radioactive super-heavy elements. Let’s understand what drives this amazing diversity in the p-block.
The Early P-block Region
Early attempts to tabulate the elements by Mendeleev and others placed what we now call the p-block elements adjacent to the s-block. These early tables were based strictly on valence, or the ratio in which each element combines with other atoms like oxygen and hydrogen. That is certainly a valid approach to organizing the elements because valence is directly tied to their atomic structure.
But even before the structure of the atom had been fully worked out, as early as 1904, certain offerings of elemental tables put groups 13 through 18 at the opposite end of the table where they appear today. These tables seemed to acknowledge that there was something different about the groups of elements beyond group 2. These groups were messy, containing elements with many different observed properties and unusual trends within each group that defied explanation at that time.
Where Are the P-block Elements Located?
For a long time, the modern table signaled this greater complexity by designating groups IIIB through VIIIB for the so-called transition metals, and another group of elements called IIIA through VIIIA for the right side of the main table. Thanks to the contributions of Erwin Schrodinger, Henry Moseley, J. J. Thompson, and others, we now understand that the source of this complexity is the complex structure of the atom itself.
In this case, it is the filling of the p-subshell and the ultimate quest of all atoms—to obtain an octet. P-block elements cross that critical boundary where losing electrons in ionic bonds and metallic bonding are beginning to give way to the addition of electrons to their cloud by sharing or accepting them as an increasingly favorable way to reach an octet.
And in more contemporary presentations of the modern table, the roman numeral system is often replaced by the system recommended by the IUPAC, which simply numbers groups 1-18 straight across. In this way of numbering, the block of elements on the right becomes groups 13 through 18.
Within those same columns, the p-block is defined as rows 2 through 7. Remember that helium is too simple to have any p-electrons at all, so it’s not considered a p-block element. So, it is these 36 elements—and only these 36 elements—that have p-electrons in their valence shell when in the ground state.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
All Major Classes of Elements in One Region
In fact, it’s amazing that just three dozen elements grouped so closely together contain all of the following: familiar metals like lead and tin, semiconductors like silicon and germanium, inert gases like neon, and life’s core building blocks, from carbon, nitrogen, and oxygen, to phosphorus and sulfur.
The first thing that should jump out at you about the p-block is that it contains all three major classes of elements—metals, metalloids, and nonmetals. Even more striking is that they are arranged in fairly neat, but predominantly diagonal patterns.
Metals are on the lower left, nonmetals are in the upper right. And there’s a diagonal metalloid zone running across the p-block that you might think of as a friendly kind of ‘demilitarized zone’, where the properties of metals and nonmetals come together in peaceful and surprising ways.
The Lower-left Corner
The elements of row 7 in the p-block are another special case. Although their location predicts metal-like properties, there isn’t much we can say about the chemical properties of these so-called ‘superheavy’ elements with confidence, since only a handful of atoms of them have ever been made.
In the lower-left corner of this region of the p-block, some of the most familiar metals in our world appear. These metals include lead, tin, and aluminum. These are all classic metallic elements that often form ionic compounds with nonmetals, and that share electrons with other metals through the valence band in metallic bonding. As metals, they are malleable and conduct electricity and heat well, just like most other metals.
A Block with the Most Diversity
But on the other side of the p-block are nonmetals like carbon, oxygen, sulfur, and chlorine. These elements prefer to bond covalently with one another to make discrete molecules in compounds. Compounds like the solvent chloroform (CHCl3), or the gas carbon dioxide CO2, or the pollutant sulfur trioxide, which causes acid rain.
Crossing through the middle of the p-block are some more familiar elements, like silicon for example. These elements represent a gray area of the p-block, in which properties are somewhat similar to metals, but others are more like the nonmetals.
Common Questions about the P-block of the Periodic Table
In general, the periodic table consists of 18 groups, of which the elements of groups 13 to 18 have p-electrons in their valence shell. Thus, groups 13 to 18 form the p-block region of the periodic table. Within the groups 13 to 18, the p-block covers rows 2 to 7, which are a total of 36 elements.
Some familiar metals in the world are located in the lower-left corner of the p-block, with metals such as aluminum, lead, and tin being among these. These classic metallic elements often form ionic bonding with nonmetals and covalent bonding with other metals. Similar to other metals, malleability and conductivity are some properties of these elements.
Some nonmetal elements in the p-block region tend to bond covalently with one another to create some discrete molecules in compounds. Sulfur, oxygen, carbon, and chlorine are among these nonmetal elements, which can form compounds such as carbon dioxide (CO2), the solvent chloroform (CHCl3), and the pollutant sulfur trioxide together.