Group: definition in chemistry
Group: A vertical column of the periodic table. Elements in the same group usually have the same number of outer electrons and similar chemical properties.
Modern tables number the groups from 1 to 18, though older systems used Roman numerals with the letters A and B. Because group members share a pattern of valence electrons, they react in similar ways, while properties such as atomic size and metallic character change steadily down the group. Several groups have their own names, including the alkali metals, alkaline earth metals, halogens and noble gases.
Examples
- Group 1 — the alkali metals, such as sodium and potassium
- Group 2 — the alkaline earth metals, such as magnesium and calcium
- Group 17 — the halogens, such as chlorine and iodine
- Group 18 — the noble gases, such as neon and argon
On the periodic table
The 18 groups run from left to right across the table, and the group number is usually printed at the top of each column.