Group 7: The Halogens

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In this lesson, we will learn

• what are halogens?
• physical properties of halogens
• chemical properties of halogens

What are the Halogens?

The halogens are the five non-metals in Group 7 of the Periodic Table – fluorine, chlorine, bromine, iodine and astatine. Astatine is highly radioactive and extremely rare.

The elements in Group 7 are:

Chemical Name	Chemical Symbol	Atomic Number
fluorine	F	9
chlorine	Cl	17
bromine	Br	35
iodine	I	53
astatine	At	85

Physical Properties of halogens

• Are poisonous
• Brittle and crumbly in their solid form
• Do not conduct electricity
• Form diatomic molecules (containing two atoms). For example Fl2.
• Form colored vapors.
• Fluorine is a pale yellow gas
• Chlorine is a green gas
• Bromine forms a red vapor
• Iodine forms a purple vapor

Chemical Properties of halogens

• The halogens are among the most reactive elements in the Periodic Table.
• They all have seven valence electrons – seven electrons in their outer-shell.
• They react with metals to form compounds called halides.

Reaction with iron wool

Halogen	Reaction with iron wool	The product	Appearance
fluorine	Iron wool bursts into flame as fluorine passes over it – no heating required.	Iron(III) fluoride, FeF3	Pale green solid
chlorine	Hot iron wool glows brightly when chlorine passes over it	Iron(III) chloride. FeCl3	Yellow solid
bromine	Hot iron wool glows, but less brightly, when bromine vapor passes over it.	Iron(III) bromide, FeBr3	Red-brown solid
iodine	Hot iron wool shows a faint red glow when iodine vapor passes over it.	Iron(III) iodide, FeI3	black solid

Reactivity increases as you go up Group 7

When halogens react with metals, the halogen atoms gain an electron. The smaller the atom the easier it is to attract the electron and the more reactive the element. (This is opposite of the trend in Group 1 where the larger the atom the easier it is to lose an electron.)

Halogens form Ionic and Covalent Compounds

Since halogens have seven electrons in their outer shell, their atoms are only one electron short of a full shell. A halogen atom can gain an electron by accepting an electron from another atom, or sharing an electron with another atom.

Halogens form ionic compounds with metals

When reacting with metals, a halogen atom accepts an electron from the metal atom. The metal atom becomes a positive ion and the halogen atom a negative ion.

Example:

Na + Cl → Na⁺Cl^-

Halogens form covalent compounds with hydrogen and non-metals

When reacting with hydrogen and other non-metals, the halogen atoms share electrons, forming molecules with covalent bonds. Halogens can also form covalent bonds with each other to give diatomic atoms.

Example:

H₂ + Cl₂ → 2HCl

Physical Properties of the halogens

Chlorine, bromine, iodine

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Fluorine

This video shows fluorine reacting with different elements.

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Chlorine

The following video shows a reaction between sodium and chlorine. An Erylmeyer flask is filled will chlorine gas by the reaction of hydrochloric acid and potassium permanganate. Sodium metal is placed into the flask and the reaction is catalyzed when a few drops of water is placed on the sodium metal in the flask. What results is an exothermic reaction that produces a white smoke full of NaCl or sodium chloride dust.

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Bromine

The following video shows bromine reacting with aluminum. Small lumps of aluminum are added to bromine. The two elements start reacting after a short activation period, forming solid aluminum bromide. The reaction is very exothermic

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Iodine

The following video shows how iodine reacts with aluminum powder. After a few minutes, the two start reacting to produce a toxic purple cloud of iodine vapor, aluminum iodide, and a little hydrogen iodide.

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