Structure of the Modern Periodic Table

The Modern Periodic Table is arranged in order of increasing atomic number, which is the number of protons in the nucleus of an atom. The lightest atom is Hydrogen, in the upper left-hand corner, with an atomic number of 1. This means that hydrogen contains only 1 proton in its nucleus. The heaviest naturally occurring element is Uranium, with an atomic number of 92. The major difference between hydrogen and uranium is the number of protons in their nuclei. The heaviest human-made element is atomic number 118, UUo, known as Ununoctium (from its atomic number “one” “one” “oct,” or eight.). UUo’s discovery (or creation) was announced on October 9, 2006, as a result of collisions between californium-249 atoms and calcium-48 ions. It is believed to be a semi-conducting noble gas.

The Periodic Table consists of rows and columns. The rows are called Periods and denote energy levels of the elements’ outermost electrons. For instance, both hydrogen and helium have their outermost (and only) electrons in the first energy level, which is why they are in the first row the Periodic Table. The second row elements lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon, each have their outermost electrons in the second energy level, and so on. This is a general rule for each element in a row, but there are notable exceptions which will be discussed later.

The columns are called Groups or Chemical Families. All elements in a a given column or group share similar chemical properties. All the elements in the far-right column are the Noble Gases. These gases generally do not react with other elements.



There are two general classifications to know about the elements on the Periodic Table, before diving in and looking at individual groups of elements. These two classifications are Metals vs. Non-Metals, and Representative elements vs. Transition elements.

Metals vs. Non-Metals. Most of the elements on the Periodic Table are metals. Metals begin on the left-hand side of the table, and extend all the way to the right, until the stair-step line. To the right of the stair-step line are the non-metals, far fewer in number. Along the stair-step line are the semi-metals, also known as metalloids. The semi-metals are Boron (atomic number 5), Silicon (14), Germanium (32), Arsenic (33), Antimony (51), Tellurium (52) and Polonium (84).

Representative Elements. The representative elements are groups 1-2, and 13-18.

Transition Elements. The groups in-between, 3-12, and the ones down below the table consist of the transition elements. The transition elements can also be broken into two sections. Groups 3-12 are referred to as the transition metals, and the two rows of elements below the main table (atomic numbers 58-71 and 90-103) are the inner transition metals. The first row of the inner transition metals (atomic numbers 58-71) are known as the Lanthanides, because their first element is Lanthanum, and the second row (atomic numbers 90-103) are called the Actinides, because their first element is Actinium. The names are a little deceptive because, depending on the Periodic Table you’re looking at, the elements actinium and lanthanum themselves are often placed among the transition metals, not the inner metals.