Covalent bonding

An ionic bond was described in previous posts on this blog. Now I want to focus on a covalent bond. This is different from an ionic bond in that it is not an attraction of a positive and negative charge on two atoms.

Notice how in these covalently bonded molecules above, the atoms of the basic unit have a distinct shape with bond angles. These distinct molecules are generally not held together in a rigid lattice structure (at room temperature) that looks like this: (for ionic bonding)

The structures in green, red and black are ionically bonded lattice structures while the sulfur dioxide and carbon dioxide above covalently bonded shapes.

If you put them next to each other (to compare) they look like this (see below):

Can you tell which structures are ionic lattices and which are covalent? In the final diagram the two structures are mixed together.

Ionic Bonding Part II

Compounds that fall into the ionic bonding category tend to have certain traits. Some of these traits are as follows:

1. Made of a metal and nonmetal combination. Often metals form + charges and nonmetals form - charges that fit together in a neutral ionic bond.
2.  Tend to be brittle solids- think of things like egg shells that are hard to the touch but crack and break fairly easily
3.  If soluble, dissolve in solution to make a solution that conducts electricity.

Here is a picture of table salt dissolved in water. The "electrolytes" exist in water as Na+ and Cl-. These ions conduct electricity. (Don't ever leave your hairdryer in water for this reason.)

Have you ever dissolved table salt in water? It looks like a clear solution if you don't add too much. This clear solution is made of positively and negatively charged ions that look like this picture.

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.