To study ionic bonding in detail we need to be clear about the definition of an ion. Whenever atoms gain or loose electrons, electrically charged particles are formed which can be positive or negative. They are called ions and have the same electronic structure as noble gasses. Metals form positive ions and non metals form negative ions.
Formation of Ions
Ions are electrically charged particles which are formed when atom gain or loose electrons. Metal and non metal atoms go in opposite direction when they ionise. Metals – loose electrons in their highest energy level and become positively charged ions.
|Image source : BBC.co.uk
|In the figure above we can see that sodium has an electronic configuration of 2,8,1. Sodium atom looses an electrons and got a noble gas configuration of 2,8 and formed a positive sodium ions.
|Image source : BBC.co.uk
Image source : BBC.co.uk
|Image source : slideshare.net
Example – Sodium(metal ) + Chlorine(non-metal) = Sodium Chloride (ionic compound)
In this process the metal atoms become positive ions and the non metal atoms become negative ions. Between the positive and the negative ions there is a strong electrostatic force of attraction called ionic bond.
Group 1 and Group 7
The elements in group 1 are known as alkali metal. They form ionic bond with non – metals . Their ions have a single positive charge .
Example : Na+
The elements of group 7 are called halogens . They form ionic compound when they react with metals and their ions have a single negative charge .
Example : Cl-
Dot and cross diagrams
|Image courtesy: BBC.co.uk
Sodium ion have a positive charge by loosing one electron represented by red dot. Whereas chloride ion has a negative charge as it gained an electron from sodium to make the complete outer shell like noble gases.
Constructing Formula Of Ionic Compounds
The formula can be worked out easily if the ions in it are known. For example: the compound formed from Na+ and SO42- will have 2 Na+ ions to every one SO42- so that the overall compound is neural. Hence the formula : Na2SO4. Symbols and number shows the atom in the compounds. For example : ZnCO3 has one zinc atom and one Carbon atom bonded with three oxygen atom.
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