Last updated 8-5-09
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4: The Building Blocks of
Inorganic Compounds

Inorganic compounds are those substances that do not ordinarily come from living things. For example, the cement in Hoover Dam, the metal used to help build the dam, and the surrounding rocks are not produced by living organisms. The water, also, is usually considered an inorganic compound even though living things need it. The asphalt highway, however, contains organic compounds because the asphalt came from petroleum, which is a decomposition product of ancient forests or algae.
Oxygen 46%
Silicon 28%
Aluminum 8%
Iron 6%
Calcium 4%
Sodium 2.4%
Magnesium 2.3%
Potassium 2.1%
Titanium 0.6%
Hydrogen 0.14%

To better understand the building blocks of inorganic compounds, let's look at the 10 most abundant elements in the Earth's crust. Oxygen is the most abundant by far, so you would expect oxygen to be involved in building blocks for inorganic compounds. Silicon is the second most common, so it's not surprising that silicon bonded with oxygen is a very common building block.

When you look at a mountain, be aware that about 50% of it is oxygen and when combined with silicon, the two make up 75% of that mountain. Silicon usually bonds to two oxygens. If this building block repeats, you get quartz- a very common mineral. The name for silicon with two oxygens is silicon dioxide (silica). This is also the main ingredient of glass. The difference between quartz and glass is that in quartz the stacking of silicon dioxide is regular and forms a crystal. In glass, the stacking of silicon dioxide is irregular (non-crystalline) plus they often add other inorganic compounds to glass to get it to melt easier.
The formula for silicon dioxide is SiO2. Silicon is actually bonded to four oxygens, but those oxygens are bonded to other silicon atoms. So the average is one silicon for every two oxygen atoms. My graphic is trying to show the 3-dimensional stacking of silicon dioxide.
Common metal
Chemical name when combined with silicon and oxygen (silicate)
Mineral name


Aluminum silicate
Iron silicate
Calcium silicate
(calcium iron silicate)
Sodium silicate

Magnesium silicate
Potassium silicate
Titanium silicate
(titanium calcium silicate)
Kyanite & Sillimanite
Andradite (if with iron)
Water Glass and Silica Gel
Silica Gel
Titanite (if with calcium)
"Silicates" is a general term for minerals that have silicon and oxygen, but also may contain a metal or sometimes hydrogen. They are the largest class of minerals.To the left are the metals listed in the top 10 most abundant elements. Each one of them can be bonded with silicon and oxygen. Just say aluminum silicate, iron silicate, calcium silicate, and you are giving the chemical name for many minerals. For example, aluminum silicate Al2SiO5 is the mineral known as kyanite. Remember that most minerals were named before they knew what elements were in them. So mineral names often reflect their color, the person who discovered it, or some other trait rather than their chemical composition.
Aluminum is the third most common element in Earth's crust, so you would expect aluminum and oxygen to bond and form building blocks. It's called aluminum oxide (Al2O3). The repeating pattern is 2 aluminum atoms and 3 oxygen atoms. The mineral, corundum, is made of aluminum oxide. It is very hard, which is why it's used in sand paper.

Because of its hardness, aluminum oxide is found in gemstones, which are valuable because they resist scratches. Aluminum oxide is the main building block for rubies and sapphires. Rubies have a trace amount of chromium, which gives it the red color. Sapphires are also built from aluminum oxide, but trace amounts of other metals give it different colors.

The three most common elements are combined with other elements to build many minerals. Topaz is (AlF)2SiO4 meaning "Aluminum and fluorine is bonded together, and a pair of them is bonded to one silicon and four oxygens atoms." This is the repeating building block for topaz.

Emeralds are basically the same but the metal beryllium (Be) replaces the fluorine (F).

In an earlier tutorial on the history of chemistry, you learned about clay chemistry. Below is an image from that tutorial. It should not surprise you now, that the common soil known as clay is made from oxygen, silicon, and aluminum (the 3 most abundance elements). In clay, silicon dioxide and the aluminum oxide have water molecules bound to them.
The below table is a simplified version of the Periodic Table of the Elements. I've included just the elements you might have heard of. The left portion of the table are metals. The upper right corner are non-metals. The pattern of an inorganic building block is that a metal will combine with a non-metal (except for those in column 18 which are the noble [inert] gases). The reason is that non-metals (except for noble gases) are a one to four electrons short of filling their outer orbit. The metals, on the other hand, have one to four electrons loosely held in their outer orbit. So it works out nicely. The non-metals pull electrons off of the metal atom, leaving the metal atom positively charged. The non-metal now has extra electron(s) that make it negatively charged. The now hold together (bond) because of their opposite charges.
On the chart, find "Na" in column 1 (also called, "Groups"). "Na" is sodium. On the right, the non-metal, "Cl," is chlorine. They combine to form sodium chloride (common table salt). Sodium also combines with fluorine (F) just above chlorine to form sodium fluoride, which is what they put in toothpaste to fight cavities.
In the Earth's crust, all metals except gold and sometimes platinum, are found bonded to oxygen. The metal bonded to oxygen is the ore for that metal. For example, you don't find copper metal in the ground, but you do find copper oxides, which is copper combined with oxygen. So metals combined with oxygen are other examples of inorganic compounds.
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