Friday, April 6, 2012

The Ionic Bond: From Simple to Complex (Part I)

Chemical bonding is one of the most basic concepts in science. It is an excellent place to start our survey of basic chemistry.

Let's start with a basic definition of an ionic bond: A chemical bond based on the attraction of positive and negative charges of different elements.

The picture above shows the forces of attraction based on positive and negative charges. It is like electricity! An ionic bond is held together by these forces- the positive sucks the negative towards it and creates a chemical bond.

What makes ionic bonds unique? Substances that are ionically bonded tend to be in solid form more often than substances that are not ionically bonded. They also tend to form repetitive structures called lattices. These are repetitive blocks of atoms stacked together.
This picture shows the positive/negatively charged atoms stacked in a repetitive pattern.

An excellent example of a simple ionic compound is table salt. Table salt forms granular crystal that feels like sand to the touch. The following picture shows table salt in molecular and crystal form along with another salt that bonds in the same way.
Notice how both ionic structures form a pattern that is very ordered . If you broke the repetitive structure down, however, you would see a single, simple building block represented by the most basic chemical formula. In the case of sodium chloride, this is one unit of sodium for one unit of chlorine.

This picture shows the smaller building block of sodium chloride within the larger repeating structure.  (Notice the bold colors of the basic NaCl unit versus the faded color of the structure as a whole.) It is alongside methane molecules that do not form an ionic bond. The methane molecules are spread far apart from each other and not attracted to each other by positive and negative charges. (Note also that methane is a gas not a solid.)

Do you feel like you could explain an ionic bond to a friend? This would be helpful in assessing whether you truly grasp this concept.

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