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Periodic table›Science›Groups in the periodic table
Mendeleev · Science

Groups in the periodic table

Why vertical columns matter and what a group can tell you about chemical behaviour.

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What a group means

The periodic table has 18 numbered groups. A group is a vertical column. Elements in the same group often show related chemical behaviour because their valence-electron arrangements are related, but the similarity is a trend rather than an absolute rule.

Reading groups 1–18

1–18

Patterns — and exceptions

Moving down a group adds electron shells. Atomic size generally increases, while other properties such as ionization energy and reactivity change in ways that depend on the family. Hydrogen is a good reminder not to infer every property from column position alone.

Use the group as a comparison tool

Start with the group number, then compare valence electrons, common oxidation states and measured properties. Treat the group as a powerful organizing pattern, not as a substitute for element-specific data.

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Science topicsElementsLearnReference
Understand the idea

Groups in the periodic table

1 · Understand the idea2 · How to use this concept3 · Try it yourself

Start by identifying what the page is describing, which quantities or structures are involved, and what changes when one parameter changes. Separate the definition from the consequence: a scientific term is useful only when you can connect it to an observation, a calculation or a position in the periodic table.

Worked reading

How to use this concept

Read the statement once without calculating. Then list the known information, the unknown, the units and the relation that connects them. If a diagram is present, name every symbol before using it. Finally, check whether the result is physically and chemically plausible rather than accepting a number simply because the arithmetic worked.

Key point

The periodic table has 18 numbered groups. A group is a vertical column. Elements in the same group often show related chemical behaviour because their valence-electron arrangements are related, but the similarity is a trend rather than an absolute rule.

Try it yourself

Groups in the periodic table

Use the explanation above to restate the concept in one sentence, then identify one concrete example from the page. If a formula is involved, explain what each symbol means before substituting values.

Show the answer

Moving down a group adds electron shells. Atomic size generally increases, while other properties such as ionization energy and reactivity change in ways that depend on the family. Hydrogen is a good reminder not to infer every property from column position alone.