Common Elements, Compounds, and Native Metals
Common elements and compounds are the substances we meet most often in everyday life, from oxygen and iron to water and table salt, and native metals are metals found in nature as pure or nearly pure elements and not combined in ores. In brief: gold, silver, copper and platinum can occur as native metals, but most metals such as iron and aluminum are found as compounds and must be extracted from their ores.
Knowing the main elements and compounds, and where they are found, helps to connect chemistry with the world around us. This article lists the most abundant elements in the universe, Earth’s crust and the human body, describes common compounds and their uses, explains why some metals are found native and others not, includes a mass percent calculation and gives the history of metals.
Which elements are the most common?
The most abundant elements depend on where you look. In the whole universe, hydrogen and helium dominate. In Earth’s crust, oxygen and silicon are the most abundant, mainly in silicate rocks. In the human body, oxygen, carbon, hydrogen and nitrogen make up almost everything, as the body consists largely of water and organic compounds.
| Rank | Earth’s crust | Share (%) | Human body | Share (%) |
|---|---|---|---|---|
| 1 | Oxygen | about 46 | Oxygen | about 65 |
| 2 | Silicon | about 28 | Carbon | about 18 |
| 3 | Aluminum | about 8 | Hydrogen | about 10 |
| 4 | Iron | about 5 | Nitrogen | about 3 |
| 5 | Calcium | about 4 | Calcium | about 1.5 |
Values are rounded, and different sources give slightly different numbers. Hydrogen makes up about three quarters of the ordinary matter of the universe by mass.
Which compounds are common?
| Compound | Formula | Everyday use or occurrence |
|---|---|---|
| Water | H2O | Drinking, cleaning, solvent |
| Sodium chloride | NaCl | Table salt, preservation |
| Carbon dioxide | CO2 | Soft drinks, fire extinguishers, photosynthesis |
| Calcium carbonate | CaCO3 | Limestone, marble, chalk, shells |
| Silicon dioxide | SiO2 | Sand, quartz, glass |
| Sucrose | C12H22O11 | Table sugar |
| Ammonia | NH3 | Fertilizers, cleaning products |
| Sodium bicarbonate | NaHCO3 | Baking soda |
| Iron(III) oxide | Fe2O3 | Rust, main iron ore |
What are native metals?
A native metal is a metal found in nature as an element, not combined with other elements. Such metals are unreactive enough to survive in the ground without forming compounds. The best-known native metals are gold, silver, copper and platinum. Gold nuggets and flakes in river gravel are classic examples, and copper can occur as large lumps, such as in the Lake Superior region of North America.
Most metals are reactive and are therefore found as compounds, such as oxides, sulfides and carbonates. Iron is mostly found as oxides, aluminum as bauxite (an aluminum oxide ore) and sodium as sodium chloride. Reactive metals like sodium and potassium are never found native.
| Metal | Found native? | Typical natural form |
|---|---|---|
| Gold | Yes | Nuggets, flakes, veins |
| Platinum | Yes | Grains in river deposits |
| Silver | Sometimes | Native silver, also silver sulfide |
| Copper | Sometimes | Native copper, also sulfides and carbonates |
| Iron | Rarely (meteorites) | Hematite (Fe2O3), magnetite (Fe3O4) |
| Aluminum | No | Bauxite |
| Sodium | No | Sodium chloride, sodium carbonate |
How are metals obtained from ores?
An ore is a rock that contains enough of a metal compound to make extraction worthwhile. The method depends on the reactivity of the metal. Metals less reactive than carbon, such as iron and copper, are obtained by heating the oxide with carbon, which removes the oxygen. Very reactive metals such as aluminum and sodium are obtained by electrolysis of the molten compound, as the reduction with carbon is not strong enough.
Worked example: how much iron is in iron ore?
An ore sample is pure hematite, Fe2O3. What percentage of the mass is iron, and how much iron can be obtained from 1.00 tonne of the ore?
- Molar mass. Fe2O3 = 2 × 55.85 + 3 × 16.00 = 111.70 + 48.00 = 159.70 g/mol.
- Mass percent of iron. 111.70 ÷ 159.70 × 100% = 69.9%.
- Iron from 1.00 tonne (1,000 kg). 1,000 × 0.699 = 699 kg.
- A real ore. If the ore is only 60% hematite, the iron obtainable is 1,000 × 0.60 × 0.699 = 419 kg.
The calculation shows why rich ores are valuable and why mining produces large amounts of waste rock, which must be handled carefully.
How did people begin using metals?
Native gold and copper were probably the first metals used by people, since they could be hammered into shape without smelting. Native copper was used in the Near East and the Great Lakes region thousands of years ago. Smelting of copper ores began around the 5th millennium BCE, and bronze, an alloy of copper and tin, became widely used in the Bronze Age. The smelting of iron followed from around 1200 BCE onward. Aluminum, though abundant, was not isolated in a pure form until the 19th century, when it was at first more valuable than gold, and cheap production only came with the electrolytic process of 1886.
Which mistakes are common?
Mistake 1: Thinking that all metals are found as pure metals
Most are in compounds and need extraction.
Mistake 2: Confusing abundance in the universe and on Earth
Hydrogen dominates the universe, but oxygen and silicon dominate Earth’s crust.
Mistake 3: Believing that “pure” gold jewelry is 100% gold
Most jewelry is an alloy, such as 18-carat gold, which is 75% gold.
Mistake 4: Saying that rust is iron
Rust is iron oxide, a compound with different properties from iron.