So far throughout this unit, we’ve been discussing atoms as uncombined, pure substances – essentially elements. Each elements, as a consequence of its unique combinations of protons, neutrons and electrons has unique characteristic properties. These properties, while unique to individual atoms/elements, occur in very predictable, ordered ways – as sequenced on the periodic table of elements. This table is a fascinating and important tool for scientists; it’s like a guide-book to every element in the universe: it tells you how its atoms are composed, what its atomic mass and number is, what it behaves like, what elements it’s related to, etc.
The Periodic Table
The table as we know it has been under development since 1869, following the first arrangement of known atoms by Dimitri Mendeleev. He arranged atoms by their accepted atomic masses, and began to see patterns emerge as he viewed the elements and their properties side by side. He, and other scientists were also able to use gaps in the table to predict other, yet undiscovered elements.
Since the first arrangement of the periodic table, there have been several advancements and rearrangements of the table based on discoveries of new naturally occurring elements, and laboratory-composed elements. Our modern table now contains all the elements known, arranged by atomic number from left to right.
Arranging the Table
The periodic table is arranged in several ways – the first, and most general is by rows and columns.
Rows = Periods
Each horizontal row of elements (from left to right) on the periodic table is called a period.
The properties of elements changes in similar ways across rows of the periodic table. As you move from left to right, elements become increasingly less reactive, turn to metalloids and non-metals, and end in noble gases.
This common trend of characteristic change across rows is called “periodicity.”
Columns = Groups
Each vertical column of elements (from top to bottom) on the periodic table is called a group.
Elements in the same group have very similar properties because they have the same number of electrons in their outermost shell. Thus Lithium and Rubidium will behave similarly, as will Neon and Argon.
The table is also broken down into categories. In general, there are 3 main categories on the periodic table, each of which may be broken down into subcategories.
- Metals
- Non-Metals
- Metalloids
Metals
Most elements in the world are metals. Metals are found to the left of the “zigzag” line on the periodic table (the “B, Si, Ge-As, Sb-Te” metalloid divider).
In general, metals have the following properties: they are shiny, conduct heat and electricity well, malleable & ductile.
Examples of metals include: Iron, Nickel, Cobalt.
The Periodic Breakdown of Metals
Group 1: Alkali Metals
Alkali metals are the most reactive metals. They respond violently to water as they freely join with other elements to make a stable outer shell, often resulting in highly energetic reactions.
Group 2: Alkaline Earth Metals
Alkaline-earth metals are less reactive than alkali metals are. Soft, silvery metals that conduct electricity well.
Group 3-12: Transition Metals
Transition metals include those we are most familiar with: zinc, silver, gold, etc. They tend to be shiny, malleable and conduct thermal energy and electric current well. These metals are able to place up to 32 electrons in their second to last shell, and can use the two outermost shells/orbitals to bond with other elements. It’s a chemical trait that allows them to bond with many elements in a variety of shapes.
Lanthanides and Actinides
Elements in the first row that follow lanthanum are called lanthanides. These are also called rare-earth and inner-transition metals. These can be found naturally (though rarely, considering the name!) on earth.
Elements in the second row that follow actinium are called actinides.
These are are all radioactive and some are not found in nature. Some of the elements with higher atomic numbers have only been made in labs.
Poor Metals
The poor metals (post-transition metals) are some metallic elements of the p-block of the periodic table that are more electronegative than the transition metals. Their melting and boiling points are generally lower than those of the transition metals, and they are also softer. They are distinguished from the metalloids, however, by their significantly-greater boiling points in the same row.
These include: Aluminum, Gallium, Indium, Tin, Thallium, Lead, Bismuth, and Polonium.
Non-Metals
Nonmetals are found to the right of the zigzag line on the periodic table (the “B, Si, Ge-As, Sb-Te” metalloid divider). They are a varied group of elements, ranging from reactive solids to inert gases. In general though, they are all dull in appearance, do not conduct heat or electricity well, and are brittle and unmalleable. They are also somewhat rare.
Examples of this group include: Sulfur, Iodine, Neon.
The Periodic Breakdown of Non-Metals
Group VII A: Halogens
These elements are all one electron away from having full outer shells. Because they are so close to being complete, they have freely combine with many different elements (are very reactive). They often bond with metals and elements from Group One of the periodic table, forming Halides.
Group VIIIA: Noble Gases
All inert gases (or noble gases) are located in the far right column of the periodic table, in Group Zero (Group 0) [or Group Eighteen (Group XVIII)]. Elements in this group are unreactive – they do not combine with other elements freely because they have full outer shells with eight electrons (except for Helium, which has 2).
Metalloids
Metalloids, also called semiconductors, are the elements that form the “zigzag” line on the periodic table (the “B, Si, Ge-As, Sb-Te” metalloid divider).
These elements have some properties of both metals and nonmetals.
Some are shiny, some are dull, they are somewhat malleable and ductile, and some conduct heat and electricity. In general, they take on the properties of their group.
Examples of metalloids include: Silicon, Boron, Antimony.
An interactive view of the periodic table is below.
Click the image below to explore the properties of individual elements, bonding and practice your skills with atomic number, mass and electron configuration.
