GROUP 17: THE HALOGENS

Halogens Overview

Also known as: Salt-formers

Elements: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At), Tennessine (Ts)

Common Properties: Seven valence electrons (ns²np⁵), highly reactive nonmetals, form salts with metals

F

Fluorine

Most Reactive
Atomic Number 9
Atomic Mass 19.00 u
Electron Config [He] 2s² 2p⁵
Common Ions F⁻
Melting Point -220°C
Density 1.70 g/L (gas)
Fluorine is so reactive that it can burn things that are normally fireproof, like asbestos and water! Early researchers called it the "devil's element."

Properties: Pale yellow gas, most reactive element, diatomic (F₂)

Applications: Toothpaste, Teflon, refrigerants, uranium processing

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Cl

Chlorine

Disinfectant
Atomic Number 17
Atomic Mass 35.45 u
Electron Config [Ne] 3s² 3p⁵
Common Ions Cl⁻
Melting Point -101°C
Density 3.21 g/L (gas)
Chlorine was used as a chemical weapon in World War I, but today it safely disinfects drinking water for billions of people!

Properties: Greenish-yellow gas, toxic, diatomic (Cl₂), strong oxidizing agent

Applications: Water purification, PVC plastic, disinfectants, solvents

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Br

Bromine

Liquid
Atomic Number 35
Atomic Mass 79.90 u
Electron Config [Ar] 3d¹⁰ 4s² 4p⁵
Common Ions Br⁻
Melting Point -7°C
Density 3.12 g/cm³ (liquid)
Bromine is the only nonmetallic element that is liquid at room temperature, and its name comes from the Greek word for "stench" because of its strong smell!

Properties: Red-brown liquid, volatile, diatomic (Br₂), toxic

Applications: Flame retardants, photography, water treatment, medicines

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I

Iodine

Violet Vapor
Atomic Number 53
Atomic Mass 126.90 u
Electron Config [Kr] 4d¹⁰ 5s² 5p⁵
Common Ions I⁻
Melting Point 114°C
Density 4.93 g/cm³
Iodine gets its name from the Greek word for "violet" because of the color of its vapor, and it's essential for thyroid function in humans!

Properties: Shiny purple-black solid, sublimes to violet gas, diatomic (I₂)

Applications: Antiseptics, iodized salt, dyes, pharmaceuticals

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At

Astatine

Rarest
Atomic Number 85
Atomic Mass [210] u
Electron Config [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵
Common Ions At⁻
Melting Point 302°C
Half-life 8.1 hours
Astatine is the rarest naturally occurring element in Earth's crust - there's less than 1 ounce of it in the entire Earth at any given time!

Properties: Radioactive, rare, metallic appearance

Applications: Cancer treatment research, radioactive tracers

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Ts

Tennessine

Synthetic
Atomic Number 117
Atomic Mass [294] u
Electron Config [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁵ (predicted)
Common Ions Ts⁻ (predicted)
Half-life ~50 ms
Stability Synthetic
Tennessine is named after Tennessee, USA, where the Oak Ridge National Laboratory contributed to its discovery - it's only the second element named after a US state!

Properties: Synthetic, radioactive, extremely unstable

Applications: Scientific research only

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