Atomic Number
17
Element 17
Chlorine (Cl)
Chlorine is a chemical element with symbol Cl and atomic number 17. It is the second-lightest of the halogens. Its properties are mostly intermediate between those of its periodic table neighbors fluorine and bromine.
Atomic Mass
35.45 u
Category
Halogen
Period
3
Group
Group 17: halogens
Phase
gas
Density
0.003214 g/cm3
Electron Shells
2, 8, 7
Atomic Structure
Protons: 17. Electrons: 17. Neutrons: Varies by isotope.
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁵
Why Chlorine Matters
Chlorine helps connect atomic number 17, halogen behavior, period 3 trends, and electron shell structure. Its gas phase, atomic mass of 35.45 u, and electron configuration 1s² 2s² 2p⁶ 3s² 3p⁵ make it useful for comparing bonding patterns across the periodic table.
Discovery and Occurrence
Chlorine was discovered 1774 by Carl Wilhelm Scheele. Chlorine is a chemical element with symbol Cl and atomic number 17. It is the second-lightest of the halogens. Its properties are mostly intermediate between those of its periodic table neighbors fluorine and bromine.
Safety and Handling Context
Chlorine belongs to the halogen family, where many pure elements are reactive and irritating or toxic at high concentrations. Classroom work should use approved compounds and teacher guidance.
Related Elements
Frequently Asked Questions
- What is the atomic number of Chlorine?
- Chlorine has atomic number 17, which means a neutral atom has 17 protons and 17 electrons.
- What is the chemical symbol for Chlorine?
- The chemical symbol for Chlorine is Cl.
- What category is Chlorine in?
- Chlorine is classified as a halogen and sits in period 3 of the periodic table.
Explore Chlorine in 3D
Use the interactive table above to rotate atomic models, compare periodic trends, and move from Chlorine to neighboring elements without losing your place.