What is Sulfate? - Definition, Structure & Formula

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  • 0:00 What Is a Sulfate?
  • 1:38 Sulfate Structure
  • 3:24 Sulfate Formula
  • 4:32 Lesson Summary
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Lesson Transcript
Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

From drinking water to those rain showers on a cloudy day, sulfate is abundant in our environment. In this lesson, we'll explore more about this compound, its structure and formula.

What Is a Sulfate?

You've probably tasted it without even knowing it. Sulfate is highly abundant in our environment, found naturally as minerals in the earth. I am sure you are pretty interested in learning more about this molecule, so let's start with the background of sulfate.

Sulfate is a chemical compound that is composed of one sulfur atom with four oxygen atoms surrounding it. When you see sulfate, the first thing you should think about is the shape of a star with sulfur in the middle. The four oxygen atoms that surround sulfur, form that star shape. We will learn more about the structure of sulfate a little later.

Best friends with another organic compound called sulfuric acid, sulfates are considered to be salts whenever they are hanging out with sulfuric acid. Another unique property of sulfate is its ability to link up to metals. By using its oxygen atoms as ligands, or arms, the sulfate ion will reach out to a metal forming a bridge or connection. This connection of a chemical compound bonding with a metal is called a chelate. As you can see here, when sulfate takes the title of a chelating substance, the negatively charged oxygen atoms will reach out to grab a hold of the metal, iron. The result of this is the formation of a metal-ion complex called iron2sulfate, or FeSO4.

Diagram 1: Sulfate As A Chelating Agent With The Metal Ion, Iron (Fe2+)
sulfate chelate

Because sulfate has so many electrons, it can either use one pair of electrons to connect with the metal or multiple pairs of electrons. When one pair of electron is used, this is called a monodentate ligand. When more than one pair of electrons are used this is called a multidentate ligand.

Sulfate Structure

It's important to understand the structure and bonding of sulfate. Mentioned earlier, four oxygen atoms collectively form a star shape around a sulfur atom to make sulfate. In chemistry this star shape is referred to as a tetrahedral arrangement. This type of arrangement happens when you have one atom in the center and four atoms located at equal distance from each other, a 109.5 degree angle.

Now that we understand the bonding arrangement, how about we shift gears and focus on the structure of sulfate. Before you break out that pencil and start drawing your Lewis structure of sulfate, don't forget to jot down the formal charges and total number of valence electrons needed for sulfate. When I count the number of valence electrons, using the periodic table, I get the following:

  • Oxygen atom: 6 valence electrons x (4 oxygen atoms) = 24 +2 electrons = 26 total
  • Sulfur atom: 6 valence electrons. 6 + 26 = 32

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