Introduction to the Periodic Table

The periodic table is an organized chart of all the known chemical elements — the pure substances that everything is made of, like hydrogen, oxygen, and gold. It is not just a list: the table arranges the elements so that their positions reveal their properties. Learning to read it is one of the most useful skills in chemistry.

Three ideas explain the whole layout:

• Atomic number order. Elements are placed in order of their atomic number — the number of protons in the atom — increasing from left to right and top to bottom.
• Periods (rows). Each horizontal row is a period. There are seven periods.
• Groups (columns). Each vertical column is a group, or family. Elements in the same group have similar chemical properties, which is what makes the table so powerful for making predictions.

Every element has its own box showing four things: the atomic number (protons), the one- or two-letter symbol, the name, and the atomic mass. Those symbols are the same ones you use when you write chemical formulae.

The table is also split into broad regions. Most elements are metals (on the left and center) — shiny and good conductors. Nonmetals sit on the upper right. A narrow staircase of metalloids runs between them, with properties of both.

Because position predicts behavior, the periodic table lets you estimate an element's properties just from where it sits. Working with the very large and very small numbers in chemistry is easier with scientific notation, another core intro skill.

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