What is the Molar Mass of Aluminum? How Does it Compare to Other Elements?

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Imagine a world without aluminum. This metal, the most abundant on the planet, makes up more than eight percent of the Earth’s crust. We use aluminum, also known as aluminium in the United Kingdom, to make innumerable products. These include aluminum foil, cans and other containers, computers and other electronics, buildings, airplanes, refrigerators and air conditioners, medical equipment, car parts, and so much more. And yet, aluminum as we recognize the metal, is not found in nature. Instead, aluminum forms compounds such as oxides, from which we must extract the useful metal using considerable energy.

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In this article you will discover the molar mass of aluminum, symbol Al. We will explore what that means and why it is important. Every pure substance, meaning every element and every compound, has a molar mass. The substance’s molar mass influences its physical and chemical properties. The molar mass of a substance is simply the mass, in grams, of one mole of that substance.

A mole, in chemistry, is a specific quantity of particles. These particles may be either atoms or molecules. The number of particles in a mole is constant, meaning it is the same every time. The exact number of particles in each mole of a substance is approximately 6.022 × 1023 units, also known as Avogadro’s number or Avogadro’s constant. This constant is named for an Italian scientist, Amadeo Avogadro, who first described the number and its significance. Avogadro’s number is essential to understanding chemistry and how the world works.

The molar mass of aluminum is approximately 26.98 grams per mole. This value is derived from the atomic weight of the element as shown on the periodic table. One mole of aluminum atoms, or 6.022 × 1023 aluminum atoms, has a mass of approximately 26.98 grams. To understand this better, let’s compare aluminum to the smallest known element, hydrogen. One mole of hydrogen atoms has a molar mass of approximately one gram.

Hydrogen is the first element on the periodic table. Each atom of hydrogen has only one proton and no neutrons. Hydrogen also has one electron, but tiny electrons have negligible mass. The single proton, however, has a mass of approximately one atomic mass unit. One mole of hydrogen atoms has a mass of 1.00784 grams per mole, which for most purposes can be rounded to 1 gram per mole.

Aluminum is the 13th element on the periodic table. It has an atomic number of 13, with exactly 13 protons. Virtually all of the aluminum atoms in nature occur as the stable 27Al isotope and have 14 neutrons. A tiny proportion occurs as the radioactive isotope, 26Al, which has 13 neutrons. Because both protons and neutrons have the same approximate mass, and electrons have a negligible mass, we can expect that the molar mass of 27Al, with 13 protons and 14 neutrons, would be about 27 grams per mole. The calculated mass of one mole of aluminum atoms is slightly less, at approximately 26.98 grams per mole, because the small percentage of naturally occurring 26Al atoms skews the molar mass just slightly lower.

Most elements on the periodic table exist in more than one known form. Some of these forms are found in nature, while others can be manufactured in the lab. These different forms of each element, called isotopes, have the same number of protons. However, each isotope has a different number of neutrons. Aluminum has 22 known isotopes, with as few as nine neutrons to as many as 30. Most of these are unstable, short-lived and not found in nature. Only 27Al, with 14 neutrons, and 26Al, with 13 neutrons, exist in nature. And the stable 27Al isotope comprises nearly 100 percent of the naturally occurring aluminum atoms.

To determine the molar mass of an element, one must calculate an average of all the different naturally occurring isotopes of that element. But that average must also take into account the percentage of naturally occurring atoms that each isotope represents. For aluminum, 27Al accounts for far more than 26Al, with 26Al representing less than 1 percent of the naturally occurring element.

Imagine that aluminum atoms were oversized bowling balls, with the vast majority, nearly 100 percent, weighing 27 pounds. Now imagine that a tiny proportion of these bowling balls weighed just a bit less, coming in at 26 pounds. If you averaged the weight of all these giant bowling balls, that total would be very close to 27 pounds, because only a few of the balls would be underweight, skewing the average down slightly. That’s a lot like how determining the average molar mass of aluminum works. When factoring in the percentage of 26Al versus the percentage of 27Al, the more abundant 27Al isotope is weighted much more heavily. Thus the molar mass is very close to 27 grams per mole.

For elements with more than one naturally occurring isotope, the molar mass is actually an average of the atomic masses of each isotope, in the percentage in which they are found in nature, and then expressed in grams. In other words, multiply the percentage of each isotope by its individual molar mass, and then add the totals for each isotope together to find the average molar mass.

In chemistry, one must know how to convert moles of a substance to grams. Converting moles of any pure substance, whether an element or a compound, to grams is pretty easy. Simply multiply the number of moles of the substance times its molar mass, expressed in grams per mole. The moles cancel, leaving the answer in grams. Let’s use aluminum as an example.

How would we calculate the number of grams in 3 moles of aluminum? Simply multiply the number of moles of aluminum times the molar mass as shown below:

3 moles Al × 26.98 grams of Al / 1 mole Al = 80.94 grams of Al

For compounds, such as aluminum oxide, the process requires an extra step. First, one must calculate the molar mass of the compound. The aluminum oxide molecule, Al2O3, contains two aluminum atoms and three oxygen atoms. The molar mass of aluminum oxide is equal to that of the two aluminum atoms, or 26.98 × 2, plus that of three oxygen atoms, or 15.999 × 3. That equals 101.957 grams per mole of Al2O3. Knowing this number, it is easy to convert any number of moles of this compound to grams by just multiplying 101.597 g/mol times the number of moles.

Aluminum is not found in nature in its elemental form. It occurs naturally in compounds, such as aluminum oxide. Aluminum is the most abundant metal on the planet, comprising about eight percent of the Earth’s crust. People must extract aluminum from ores, particularly bauxite which contains various oxides, including aluminum oxide. Extraction of pure aluminum from bauxite requires multiple steps and considerable energy in the form of heat.

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Aluminum metal has a low density and light weight. It can be polished to a high shine, and can easily be hammered or extruded into wires, coils and thin sheets. You probably have a roll of aluminum foil in your kitchen right now. Notice that even though the metal is very thin and easy to tear or crumple, it is still strong and durable. It conducts both heat and electricity very well, and it recycles easily. Aluminum on its own is a relatively soft metal, but it forms very strong alloys with other metals. These alloys prove useful in construction, transportation, and many other arenas.

Aluminum forms compounds with many other elements or ions. We use many of these compounds commercially in a wide variety of products. People use aluminum hydroxide, Al(OH)3, to treat heartburn and indigestion, and also to treat burns and wounds on the skin. One of the ingredients in many antiperspirants, aluminum chlorohydrate, helps keep underarms dry.

Aluminum oxide, Al2O3, is a fascinating compound. Sometimes aluminum oxide presents as a powdery white coating on the surface of aluminum, where the metal has reacted with oxygen. It also naturally occurs as a colorless crystal with a hexagonal structure known as corundum.

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Corundum, the second hardest naturally occurring mineral, has a score of nine on the Mohs scale, second only to diamond. It is often imbued with other compounds, including oxides of chromium, iron, and titanium, which result in colored crystals. Red rubies and sapphires in colors including pink, blue, yellow, and black are all examples of colored corundum with small amounts of other oxides adding one or more hues.

The periodic table is arranged in increasing order, with each element arranged by its atomic number. The atomic number of an element is the number of protons in each atom of the element. Aluminum rests in the third period in group 13, formerly known as group IIIA in the United States, just under boron. It has 13 protons in each atom, giving it the atomic number 13.

Aluminum has a molar mass just under 27 grams per mole. The closest two neighbors of aluminum are magnesium, a metal with an atomic number of 12 and a molar mass of approximately 24 grams per mole, and silicon, a metalloid with an atomic number of 14 and a molar mass of roughly 28 grams per mole. Sodium, a highly reactive metal with an atomic number of 11 and a molar mass of 22.99 grams per mole begins the third period. Phosphorus and sulfur, nonmetals, sit to the right of silicon with atomic numbers 15 and 16, respectively.

The chart below illustrates the relationships between the atomic number and the molar masses of aluminum’s neighbors in the third period of the periodic table from sodium through sulfur. These elements each have complete first and second electron shells, and between one and six electrons in the orbitals of the third shell.

Aluminum, as the elemental metal and as a variety of compounds, has more uses than one could easily list in an article of this length. Our lives would not be remotely the same without aluminum. Certainly, we could find other substances to contain our beverages and wrap our baked potatoes, but we’d have to also find other ways to construct airplanes, automobiles, air conditioners and refrigerators, most of our electronics, and so much more. We use aluminum to manufacture and package medications, cosmetics, and all sorts of foods. We are even replacing copper with aluminum in tubing and wires because, in many cases, it works better and is highly resistant to corrosion thanks to the formation of aluminum oxide on its surface.

Some researchers have raised concerns about the use of aluminum in our society. For some time, scientists believed that aluminum had a link to Alzheimer’s disease, but recent studies have failed to prove that connection. Currently, doctors caution against the overuse of antacids and other medications that contain aluminum, but are not concerned about significant absorption of aluminum from utensils or cookware.

Regardless of any potential risks, aluminum is sure to play a large role in our modern world for the foreseeable future. No other metal is as readily available and has properties as well suited to all the various uses aluminum serves. We have come to depend heavily on this lightweight metal to sustain our way of life.

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