# Connected topological group

From Groupprops

This article defines a property that can be evaluated for a topological group (usually, a T0 topological group)

View a complete list of such properties

## Contents

## Definition

### Symbol-free definition

A topological group is termed **connected** if it satisfies the following equivalent conditions:

- It is connected as a topological space.
- The connected component of the identity element equals the whole group.

### Equivalence of definitions

Definitions (1) and (2) are clearly equivalent.

### Alternative definition for a locally connected topological group

For a locally connected topological group, being connected is equivalent to having no proper open subgroup. See locally connected and no proper open subgroup implies connected

In particular, this alternate definition applies to algebraic groups equipped with the Zariski topology, as well as to Lie groups. For more, see equivalence of definitions of connected algebraic group and equivalence of definitions of connected Lie group.

## Facts

- Connected implies no proper open subgroup: The converse holds for locally connected topological groups.