Chemical Group
A chemical group (also called a family) is a vertical column in the periodic table containing elements that share the same number of valence electrons, and therefore exhibit similar chemical properties and reactivity patterns. The modern IUPAC system numbers groups 1 through 18 from left to right. Elements within a group show predictable trends: for example, reactivity increases down Group 1 (alkali metals) because the outermost electron is progressively further from the nucleus and more easily lost.
Selected groups and their characteristics
| Group | IUPAC No. | Common Name | Valence Electrons | Example |
|---|---|---|---|---|
| Alkali Metals | 1 | Alkali Metals | 1 | Na, K, Li |
| Alkaline Earth Metals | 2 | Alkaline Earth Metals | 2 | Mg, Ca, Ba |
| Halogens | 17 | Halogens | 7 | F, Cl, Br |
| Noble Gases | 18 | Noble Gases | 8 (or 0) | He, Ne, Ar |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Periodic Table
The periodic table is a tabular arrangement of all known chemical elements ordered by increasing atomic number, with elements having similar chemical properties placed in vertical columns called groups. It was developed by Dmitri Mendeleev in 1869 and serves as the foundational reference for all of chemistry. The table reveals periodic trends in elemental properties such as atomic radius, ionisation energy, and electronegativity, enabling scientists to predict the behaviour of elements and their compounds.
Alkali Metal
Alkali metals are the six elements of Group 1 of the periodic table — lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr) — each having a single valence electron that is readily lost to form a +1 cation. They are soft, shiny, highly reactive metals that react vigorously with water to produce a metal hydroxide and hydrogen gas, with reactivity increasing down the group. Alkali metals are found widely in nature as salts and are essential to biological processes; sodium and potassium ions, for example, regulate nerve impulse transmission in living organisms.
Halogen
Halogens are the five nonmetallic elements of Group 17 — fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At) — each with seven valence electrons, making them one electron short of a full outer shell and therefore highly reactive oxidising agents. They readily gain one electron to form stable 1− anions (halides) and react with metals to form ionic salts, and with hydrogen to form hydrogen halides such as HCl and HF. Halogens have important industrial and biological applications: chlorine disinfects water supplies, iodine is essential for thyroid hormone synthesis, and fluorine is used in making Teflon and fluoride toothpaste.
From Latin "groupus" (cluster, bunch), adopted into scientific terminology in the 18th century. In early chemistry, elements were classified into "families" based on similar reactions; Mendeleev formalised these as vertical columns, and the IUPAC standardised the numbering system in 1990.