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The halogens


#1

The four elements called halogens are

  1. Chlorine; Cl. a greenish-yellow gas heavier than air, corrosive,
    very poisonous and choking.

  2. Bromine; Br. A dark brown very heavy liquid gives off choking
    brown fumes extremely corrosive and poisonous.

  3. Iodine; I. Very dark brown crystals, gives off purple vapour on
    gentle heating. Corrosive and poisonous.

  4. Astertine Very rare, strongly radioactive. only available in
    very specialized laboratories Thus the halogens form a special group
    in the Atomic Table, and have similar chemical properties. Chlorine
    combines with the metal sodium to produce sodium chloride, table
    salt. Bromine forms similar salts with sodium metal, making sodium
    bromide. Iodine and sodium gives sodium iodide. All the halogens are
    highly reactive and combine with hydrogen to form corrosive acids;
    examples; Hydrochloric acid, Hydrobromic acid, Hydriodic acid. And
    of course, combine with many other basic chemicals producing salts.

A salt is produced by the combination of an acid with an alkali or
base.

And I think that is enough chemistry for now. But further questions
are quite welcome.

Cheers for now,
JohnB of Mapua, Nelson NZ


#2

G’day. As soon as I had sent the previous message on the halogens I
suddenly realised I had left out Fluorine, (put it down to a Senior
Moment) so here’s a remake:

The four elements called halogens are

  1. Chlorine; Cl. a greenish-yellow gas heavier than air,
    corrosive, very poisonous and choking.

  2. Bromine; Br. A dark brown very heavy liquid gives off choking
    brown fumes extremely corrosive and poisonous.

  3. Iodine; I. Very dark brown crystals, gives off purple
    vapour on gentle heating. Corrosive and poisonous.

  4. Fluorine; F colourless, very corrosive and reactive gas, very
    poisonous. Astertine Very rare, strongly radioactive. only available
    in very specialized laboratories Thus the halogens form a special
    group in the Atomic Table, and have similar chemical properties.
    Chlorine combines with the metal sodium to produce sodium chloride,
    table salt. Bromine forms similar salts with sodium metal, making
    sodium bromide. Iodine and sodium gives sodium iodide. Fluorine
    and sodium gives sodium fluoride.

All the halogens are highly reactive and combine with hydrogen to
form corrosive acids; examples; Hydrochloric acid, Hydrobromic
acid, Hydriodic, acid Hydrofluoric acid - the one which dissolves
glass and quartz. And of course, combine with many other basic
chemicals producing salts. A salt is produced by the combination of
an acid with an alkali or base.

And I think that is enough chemistry for now. But further
questions are quite welcome.

Cheers for now,
JohnB of Mapua, Nelson NZ


#3

Oh John! You’ve forgotten Fluorine: a pale yellow, diatomic gas.
corrosive, reacts vigorously with most oxidisable substances at room
temperature, frequently with ignition.

Incidently, patinas using chlorine to colour copper and iron are the
bane of many a conservator. The chlorine reacts with moisture and
oxygen from the air to form hydrochloric acid which in turn attacks
(very aggressively) the metal. The chlorine is not used up in the
reaction (like a catalyst) and can continue to attack the metal
until there is none left. The only way to stop the process is to
remove the chlorides entirely (soaking and changing the bathwater
frequently), remove access to moisture or oxygen. This type of
corrosion is colloquially called “Bronze disease”.

Eileen