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
Videos
Physical Properties of the halogens
Chlorine, bromine, iodine
Fluorine
This video shows fluorine reacting with different elements.
Chlorine
The following video shows a reaction between sodium and chlorine.
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
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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