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Chemical Bonding

by Ron Kurtus (revised 16 September 2015)

Chemical bonding is the process where atoms or molecules combine or bond together, usually to form a new material. The outer electron orbits or shells determine which elements or molecules combine and how well they bond together.

There are several types of chemical bonding. Heat and catalysts are often need to start the chemical bonding process. Some materials will readily combine, often giving off heat energy. They are called exothermic reactions.

Other combinations require extra energy to cause the molecules to bond. In those cases, the material is usually not very stable and a little heat or even vibration can cause the molecules to split apart, giving off energy. They are called endothermic reactions.

Questions you may have include:

This lesson will answer those questions.

Rules for outer shell

Each atom or element has electrons in orbits or shells around the nucleus. There are certain rules for how many electrons there can be in each orbit. The electrons in the outer shell are called valance electrons, because they determine the chemical properties of the element.

Like to fill shell

There is also a strange trait or rule about atoms:

Atoms "like" to have their outer orbit or shell completely filled with the maximum number of electrons allowed.

Tendency to attract

Thus if the normal number of valance electrons in the outer shell of an element is a few electrons short of completing that orbit, there will be a tendency to attract electrons to fill that orbit or shell.

Tendency to get rid

Likewise, it an atom had just one or two valance electrons, there would be a tendency to get rid of those electrons. In that case, the lower filled orbit will then be the outer orbit.

Types of bonding

The number of valence electrons in each atom determines how they will combine or bond.

A common type of chemical bonding is covalent bonding. In that situation the atoms will share one or more pairs of valance electrons, thus filling up their outer shells.

Another type of bonding is ionic bonding, where one atom gives up one or more electrons to the other atom, causing them to be positive (+) and negative (-) ions. Electrical or ionic forces bond the atoms into a molecule.

There are also several other minor types of bonding such as metal bonding and hydrogen bonding.

There are millions of possible combinations for chemical compounds using these methods. Some of these combinations can be extremely complex, especially when they involve combinations of carbon, hydrogen and oxygen, such as is seen in complex sugars and petroleum products

(For more information, see Types of Chemical Bonding.)

Requirements for combining

Sometimes heat is required for different elements or molecules to combine. For example, you have to heat up a piece of coal (carbon) before it will combine with the oxygen in the air to burn and create carbon dioxide.

Sometimes the material must be dissolved in water before a chemical reaction will occur. NaCl or table salt usually must be created in a water solution.

And sometimes what is known as a catalyst must be used to initiate a chemical reaction. Your car has a catalytic converter, which helps to burn the pollutants out of the exhaust

Exothermic reactions

The bonding process of some atoms or molecules will give off heat energy and are called exothermic reactions. Combustion is a common form of exothermic reaction. The burning of coal or a carbon product is a good example:

C + O2 → CO2 + (heat)

The resulting molecule in an exothermic reaction is usually quite stable and requires a fair amount of energy to break the molecule into its components. For example, burning Hydrogen in Oxygen results in water.

2H2 + O2 → 2H2O + (heat)

Usually, the energy from electrolysis is required to separate the hydrogen and oxygen from the water.

Endothermic reactions

An endothermic reaction requires heat or some other form of energy to cause the atoms or molecules to bond.


Nitroglycerin is a highly unstable molecule with a great amount of pent-up or potential energy that is held in place by a weak chemical bond. It is similar to dynamite and TNT, except that only a slight physical shock can release its energy.

The chemical formula for nitroglycerin is C3H5(ONO2)3. When exploded, it combines with oxygen to form the stable carbon dioxide, water and nitrogen molecules, along with the release of energy.


Chemical bonding when atoms or molecules combine or bond together to form new material. The outer electron orbits or shells determine which elements or molecules combine and how well they bond together.

Covalent bonding is the most common type of chemical bonding. Some materials will readily combine, often giving off heat energy. Other combinations are not very stable and a little heat or even vibration can cause the molecules to split apart, giving off energy.

Chemistry requires logical thinking

Resources and references

Ron Kurtus' Credentials


Chemical Bonding - Explains all about the subject

Construct a Lewis Dot Structure - Click on compound from list to see its molecular structure - from St. Olaf College

Predicting molecular polarity - Explains polar molecules

Chemistry Resources


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