What are Halogens?
Halogens are a series of non-metal elements located in
group 7 of the periodic table. The term “halogen” means
“salt-former”.
All halogens have seven electrons in their outermost shell.
They are therefore just one short of a full outer shell. This
is what makes them reactive with other elements.
They are not found in their pure state like gold, but are
found tied up in covalent or ionic compounds. They have
low melting and boiling points and do not conduct
electricity at all.
Halogens
All halogens have 7 electrons in their
outermost shell, giving them an
oxidation number of -1.
This group contains, Fluorine- a pale
yellow gas, Chlorine- a pale green gas,
Bromine- a dark brown liquid, and
Iodine- a dark purple solid.
Properties of Halogens
The vigor of the reactions in halogens decreases as
we go down the group, whereas the melting and
boiling points increase. Fluorine is one of the most
reactive existing elements, attacking inert
materials such as glass, and forming compounds
with the heavier noble gases. The high reactivity of
fluorine means that once it does react with
something, it bonds with it so strongly that the
resulting molecule is very inert and non-reactive to
anything else. For example, Teflon is fluorine
bonded with carbon.
The Halogens at Room
Temperature
The halogens exist, at room temperature, in all
three states of matter:
Solid- Iodine.
Liquid-Bromine.
Gas- Fluorine, Chlorine.
Reactions of Halogens
Halogens may either gain electrons to form
negative ions or they can form a single covalent
bond with other non metals. They do this to
become like noble gases, having a full outer
shell. The halogens can react with many metal
and non metal elements forming a number of
different ionic and covalent compounds.
Example: sodium chloride (NaCl) and carbon
tetra chlorine (CCl4).
Ionic and Covalent Bonds
During the formation of sodium chloride, a single
electron from the outer shell of sodium is transferred
to the outer shell of a single chlorine atom. Both ions
(Na+ & Cl-) are now stable having the same
electronic configuration as a noble gas. This is an
Ionic Bond.
During the formation of the covalent hydrochloric
acid, both atoms form a single covalent bond. This
sharing of electrons fills the outer shell of both
hydrogen and chlorine atoms making them both
stable.
Uses of Halogens
All the halogens are potentially harmful substances.
Fluorine and chlorine in particular are highly toxic. It
is very dangerous to ingest or breathe halogen vapor
or their solutions. They are used to kill bacteria,
which is why they are used as a sterilizer for water in
swimming pools. Chlorine compounds are used in
disinfectants like ‘dettol’. Our toothpastes contain
fluoride to kill the bacteria in our mouth. Iodine water
is also used as a disinfectant prior to surgery or to
sterilize dirty drinking water.