Dot-and-Cross Diagram for Chlorine

Introduction

Chlorine atoms have seven valence electrons, so each is one electron short of an octet in the simple shell picture. Two chlorine atoms can share a pair and both count eight electrons locally. Unlike chloride formation, this does not require one atom to accept a permanently transferred electron and become a separate negative ion.

Core explanation

Begin with two neutral chlorine atoms, each with electron arrangement 2,8,7. Their combined valence inventory is fourteen electrons. Mark one atom's seven electrons as dots and the other's seven as crosses. Use one of each to form the shared pair between the atom symbols.

After assigning the bonding pair, six electrons remain associated with each chlorine in the drawing. Arrange them as three lone pairs around that atom. Each chlorine then locally counts six lone-pair electrons plus the two shared electrons, giving an octet. Across the whole molecule, there are twelve lone-pair electrons and two bonding electrons: fourteen altogether.

The bond is single because there is one shared pair. The displayed formula Cl–Cl replaces the bonding pair with a line, while Cl₂ gives only composition. Neither the subscript two nor the two atoms implies a double bond. A double bond would require two shared pairs, which is not the standard Lewis diagram for Cl₂.

The molecule is neutral overall, so separate ionic brackets and − charges do not belong around its atoms in this drawing. Chloride, Cl⁻, is a different species with eighteen electrons. Each neutral chlorine atom in the molecule contributes seventeen electrons overall, though the covalent electron distribution belongs to the molecule rather than to isolated atoms with fixed ownership.

Fluorine, bromine and iodine molecules follow the same elementary halogen pattern: a single bond and three lone pairs on each atom. Their properties and bond strengths differ, so a common electron-counting pattern does not mean that all halogen molecules behave identically.

Step-by-step reasoning

1. Count seven valence electrons from each chlorine, giving fourteen total. 2. Put one dot and one cross into the bonding region. 3. Arrange the remaining six dots and six crosses as three lone pairs on each respective atom. 4. Check both local octets, the fourteen-electron total and overall neutrality without adding ionic charge labels.

Visual explanation

Draw Cl and Cl with one dot-and-cross pair between them. Put three paired sets of dots around the left chlorine and three paired sets of crosses around the right. A bracket labelled “one molecule” may frame the illustration, but it should not carry an ionic charge.

Real-world analogy

Two neighbouring gardens may share one boundary fence while each retains three private sides. The shared feature belongs to both descriptions without being duplicated. Chlorine's local counts similarly include a common bonding pair alongside three lone pairs assigned to each atom.

Real-world example

Elemental chlorine is commonly represented as Cl₂, whereas sodium chloride contains Cl⁻ ions. The difference is essential when reading chemical equations and properties. Chlorine in these two species has the same proton count but different electron distribution, charge context and chemical behaviour.

Why?

Why do the two local octets add to sixteen while the molecule has fourteen valence electrons? Adding local counts includes the two bonding electrons twice. Count the common pair once when auditing the total molecular inventory.

Common misconception

“Each chlorine has gained an electron, so Cl₂ is two chloride ions.” Sharing a pair is not the same as each atom independently gaining an extra electron from outside. The neutral molecule still has the electrons supplied by its two neutral atoms.

Worked example

A proposed Cl₂ diagram has one shared pair but only two lone pairs on each atom. It shows 2 + 4 + 4 = 10 valence electrons, four fewer than the available fourteen. Add one lone pair to each chlorine. The corrected drawing now gives each atom eight electrons locally and conserves the complete valence inventory.

Quick check

1. How many lone pairs are present in the whole standard Cl₂ diagram? Answer: Six lone pairs total, with three on each chlorine atom.

Exam focus

Draw all lone pairs when asked for a complete outer-electron diagram. Use one shared pair for the single bond, and keep Cl₂, Cl–Cl and Cl⁻ clearly distinguished.

Advanced insight

Lone pairs are called non-bonding in this simple diagram because they are not the shared pair forming the Cl–Cl bond. They still belong to the molecule's electronic structure and influence its interactions; “non-bonding” does not mean chemically irrelevant.

Summary

Cl₂ contains one shared pair and three lone pairs on each chlorine. Fourteen valence electrons satisfy both local octets because the bond pair is shared. The molecule is neutral and differs from chloride ions despite containing the same element.

Practice questions

1. How many valence electrons are available when two neutral chlorine atoms combine? Answer: Fourteen, from seven on each atom. 2. Does the two in Cl₂ indicate a double bond? Answer: No. It counts chlorine atoms; the molecule has one shared bonding pair. 3. Predict the elementary lone-pair count on each atom in Br₂. Answer: Three lone pairs on each bromine, alongside one shared pair forming the single bond.