Comparing Inorganic & Organic Compounds: Explanation & Practice

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

There are two fields of study within chemistry--organic and inorganic. In this lesson, we will learn the differences between organic and inorganic compounds.

Defining Organic and Inorganic

When you go to the grocery store you probably see several products proclaiming themselves to be 'organic.' While the agriculture industry has made their own distinction between what they define as organic or inorganic, chemistry would actually classify all food as organic.

In chemistry, the distinction between organic and inorganic isn't clearly defined, but generally organic compounds are ones that include carbon atoms, while inorganic compounds do not contain carbon. There are a few important exceptions to this rule, such as carbon dioxide and carbon monoxide. So, organic compounds can also be defined as molecules that make up living things, while organic compounds make up non-living things. Organic compounds includes plants and plant materials, the proteins and fat that makes up our body, and the DNA in our bodies. Inorganic compounds includes salts, metals, and related compounds.

Properties of Organic and Inorganic

There are several properties of chemical compounds that we use to compare different compounds. These properties include:

  • Solubility
  • Viscosity
  • Density
  • Conductivity
  • Reactivity

We can use these properties to compare organic and inorganic compounds. For each of these properties there are exceptions, but we will be talking about general trends.

Solubility

Most organic compounds have covalent bonds, while most inorganic compounds have ionic bonds. The ionic bonds allow inorganic compounds to dissociate into positive and negative ions in water, making them highly soluble in water. On the other hand, most organic compounds are insoluble in water, although they are soluble in other organic compounds.

Viscosity

Viscosity is based on how strong the intermolecular forces between molecules are. The stronger the intermolecular forces, the higher the viscosity. A purely hydrocarbon, organic compound will have very few intermolecular forces between them. The more other elements (such as oxygen or chlorine) are included in the structure, the more intermolecular forces the molecule will feel. But overall, the intermolecular forces of organic compounds are weak, thus their viscosity tends to be low.

Inorganic compounds tend to feel more intermolecular forces, such as dipole-dipole forces and hydrogen bonding. Thus they tend to have a higher viscosity.

Density

Density is based on the size of the molecule vs. the weight of the atoms in the molecule. Most organic compounds have a lot of hydrogen atoms because hydrocarbons are common bonds. Hydrogen has a very low density; in fact, it is the lowest density atom. Since organic compounds tend to have more hydrogen atoms than inorganic compounds, this makes organic compounds typically less dense than inorganic compounds.

Conductivity

We've mentioned how organic compounds tend to have covalent bonds, while inorganic compounds tend to have ionic bonds. The ability for inorganic compounds to ionize allows them to be better electro-conductors. Let's think about how conductivity works: it is the movement of electrons from one location to another. If there are charges (such as with ionized inorganic compounds), then the electrons can move more easily. Thus inorganic compounds are typically more conductive than organic compounds.

Reactivity

A stable organic compound is typically very unreactive - and it takes a lot to get it to react. This is because in order to break the bonds of organic compounds we are breaking covalent bonds, which are much stronger than ionic bonds. This means that inorganic compounds have a faster overall rate of reaction than organic compounds.

In reactions there are typically intermediates. These intermediates are compounds that aren't stable, but are necessary in order to get to the final product. For example, if we break a hydrogen-carbon bond on an organic compound, in order to replace the hydrogen with an oxygen we will momentarily have either a positive charge or a negative charge on the carbon. Carbon does not like holding any charges. Thus organic intermediates are highly reactive, and will quickly react with whatever is available.

Examples

So, let's look at a few organic and inorganic compounds:

  • Urea
  • Methane
  • Calcium Phosphate
  • Table salt

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