1c. Why do atoms bond together? Why don't some not bond with others?

Doc Brown's Chemistry: Chemical Bonding and structure GCSE/IGCSE/O/IB/AS/A US grade 9-12 Level Revision Notes

When atoms combine they form a chemical bond

When different elements (different types of atom) react and combine to form a compound (new substance) chemical bonds must be formed to keep the atoms together.

Once these atoms are joined together its usually difficult to separate them - unlike physical mixtures.

The atoms can join together by sharing electrons in what is known as a covalent bond.

Or, they can transfer or accept electrons to form positive and negative ions and form an ionic bond.

Metals form another kind of bond in sharing electrons called a metallic bond.

The types of are briefly explained below with links to even more detailed notes with lots of examples.

The rest of Part 1c explains why atoms bond together in the first place and then the concepts broadened out to explain the different types of bonding.

The phrase CHEMICAL BOND refers to the strong electrical force of attraction between the atoms or ions in the structure. The combining power of an atom is sometimes referred to as its valency and its value is linked to the number of outer electrons of the original uncombined atom.

Why do atoms bond together? 'electron glue'!

Some atoms are very reluctant to combine with other atoms and exist in the air around us as single atoms.

These are the Noble Gases and have very stable electron arrangements e.g. 2, 2,8 and 2,8,8 because their outer shells are full.

The first three are shown in the diagrams below and explains why Noble Gases are so reluctant to form compounds with other elements.

(c) doc b   (c) doc b   (c) doc b (atomic number) electron arrangement

All other atoms therefore, bond together to become electronically more stable, that is to become like Noble Gases in electron arrangement.

Bonding produces new substances and usually involves only the 'outer shell' or 'valency' electrons and atoms can bond in two ways.

 Why do some atoms are reluctant to bond with other atoms?

As explained above, NOBLE GASES are very reluctant to share, gain or lose electrons to form a chemical bond ie they do NOT readily form a covalent or ionic bond with other atoms.

This is because Noble gases are already electronically very stable because of their particular electron arrangement with a full outer shell.

e.g. 2,  2.8 and 2.8.8 etc.

For most other elements the types of bonding and the resulting properties of the elements or compounds are described in detail in Parts 2 to 5.

In some of the electronic diagrams ONLY the outer electrons are shown, but you will come across a wide variety of electronic details diagrams and 2D and 3D models of ionic, covalent and metallic structures.


What next?

Recommend next: Key to styles of diagrams, comparison of diagrams and models


Sub-index for: Part 1 Introduction to chemical bonding - why? how? and patterns


Index for ALL chemical bonding and structure notes


Perhaps of interest?

Important definitions in Chemistry

Group 0 The Noble Gases


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