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ThinkQuest Chemistry in room 11 > Chapter 9 > Information


Slats

Salts can be categorised as pure materials. They are dull and brittleand they have very high melting and cooking points. They conduct electricity when they are melted or in a solution.
Salts are not made up of molecules but ions. Ions are electrically charged atoms.
The best known example sodium-chloride which is the main part of cooking salt.
Sodium-chloride is not made up of sodiumatoms and chlorideatoms but ions.

These ions are, in their solid phase, very regularly organised.

Sodium-chloride consists of Na+ and Cl- ions that attrackt eachother. The substance is therefore neutral because the negative charge and the positive charge are the same. So the ratio of Na+ and Cl- ions is 1:1 so the conclusion must be there are the same number of positive and negative ions.
This means that the formula should be (Na+)1(Cl-)1 . The index 1 is not noted and this means that the brackets are not needed. To make it even more easy the formula Na+Cl- is simplified to NaCl.


There are about 100,000 known salts and they all have a high meltingpoint. Stalgmites and stalagtites in caves are examples of salts. They are mainly made up of a salt called calcium carbonate or chalk. Other examples of well-known salts are: plaster stone, copper sulphate, marble, bauxite(alluminium-ore) and rust.

 To determine the formula for a salt we first need to know the charge of the ions in the salt. This is easy for NaCl because Na has +1 and Cl has 1. Bur there are other salts with different charges. Just look at the table. 

The ions of metals (which always have the same ion-charge) are given the name of the metal.
The ion of potassium (K+) is called the potassium ion.
The name of an ion with more than one ion-charge will get a roman numeral added. The roman numeral denotes the charge of the ion. In this way Fe2+ is called the iron(II)ion A negative ion will get the suffix: -ide.

Bromine            bromide-ion
Chlorine            chloride-ion
Iodine              iodide-ion
Oxygen            oxide-ion
Sulphur            sulfide-ion 

To get the formula of a salt there are a number of steps.

find the charge of the ion involved.
write down the ions next to eachother (the metal-ion always in front).
the compound must be electrically neutral so determine the smallest ratio of ions necessary.
note the ratio-numbers to the right of the ions.
If the ratio-number is one, leave it out.

Besides simple ions there arealso complex ions. A complex ion is an electrically charged particle which consists of more than one atom. You will need to know the following complex ions:

Ammonium NH4+
Carbonate CO3 2-
Phosphate PO4 3-

Hydroxide OH-
Nitrate NO3-
Sulphate SO4 2-


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