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 |
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 |
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.
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-
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
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