Kossel-Lewis Approach To Chemical Bonding
Chapter Name : Chemical Bonding And Molecular Structure |
Sub Topic Code : 102_11_04_02_05 |
Topic Name : Kossel-Lewis Approach To Chemical Bonding |
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Sub Topic Name : Formal Charge |
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Introduction
• In case of polyatomic ions, the net charge is possessed by the ion as a whole and not by a particular atom. It is, however, feasible to assign a formal charge on each atom. • The formal charge of an atom in a polyatomic molecule or ion may be defined as the difference between the number of valence electrons of that atom in an isolated or Free State and the number of electrons assigned to that atom in the Lewis structure.
Pre-Requisites:
chemical bond, octet rule, lewis structures,
Activity:
Calcium carbonate known as limestone is made of a polyatomic ion called carbonate ion.
Real Life Question:
What is the charge of an ion if it’s made of many atoms?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
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| polyatomic ion | An ion composed of a set of atoms. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Pebbles and sticks | Make Lewis structures by using pebbles and sticks for ammonium ion and carbonate ion. |
Real life uses :
Many polyatomic ions as well as molecules such as ozone have formal charges on each atom.
Places to visit :
Limestone, chalk in school
Practical examples around us
| Examples | Explainations |
|---|---|
| Chalk | Chalk is made of calcium carbonate, carbonate being a polyatomic ion. |
What you learn in Theory:
• Formal charges help in the selection of the lowest energy structure from a number of possible Lewis structures for a given species.
What you learn in Practice:
Atoms which neutral molecules also hold charges.