Periodic table basics: 18 groups, 7 periods and what they mean
The modern periodic table has 18 groups (vertical columns) and 7 periods (horizontal rows); element properties show recurring patterns across the table.
The modern periodic table has 18 groups arranged vertically and seven periods arranged horizontally. Elements in a group often share chemical patterns because of their electron configurations, while period position reflects the progression across a row.
Groups versus periods
A group is a vertical column; a period is a horizontal row. This vocabulary appears frequently in school science and general-knowledge examinations, and reversing the two is a common mistake.
The table is organised by atomic number, not by atomic mass alone. Its arrangement reveals periodic patterns in properties such as atomic size, ionisation energy and chemical behaviour.
How to revise efficiently
Learn the 18/7 count first, then practise locating a named element by its group and period. Use an up-to-date periodic table from IUPAC or a recognised chemistry text for element symbols and atomic numbers.
This explainer is static chemistry revision. It does not claim that every element in a group behaves identically; trends have exceptions that are taught in more advanced chemistry.
Editorial note
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Frequently asked questions
How many groups and periods are in the modern periodic table?
18 groups and 7 periods.