Copyright

Sulfate: Charges, Formula, and Stucture

Andria Emerson, Danielle Reid
  • Author
    Andria Emerson

    Andria Emerson has taught high school science for over 17 years. She has a M.S from Grand Canyon University in Educational Leadership and Administration, M.S from Grand Canyon University in Adult Education and Distance Learning, and a B.S from the University of Arizona in Molecular and Cellular Biology.

  • Instructor
    Danielle Reid

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

What is a sulfate? Learn about sulfates, their properties, and the uses of their compounds. See sulfate structure with charge and chemical formula for sulfate. Updated: 10/15/2021

Table of Contents

Show

What is a Sulfate?

Sulfate is a compound made of sulfur and oxygen. Its chemical formula is {eq}SO_{4}^{2-} {/eq}.

Sulfur

Sulfur is a nonmetal located in group VI on the periodic table. Sulfur is tasteless, odorless, and is pale yellow in color. In its pure form, sulfur is a brittle solid and a poor conductor of electricity. Sulfur is not soluble in water.

Sulfate

Image of Sulfate

Oxygen

Oxygen is also a nonmetal located in group VI on the periodic table. Oxygen generally forms a diatomic molecule with one other oxygen atom to form {eq}O_{2} {/eq} making it more stable. Oxygen is a colorless, odorless gas at room temperature. Like sulfur, oxygen is a poor conductor of electricity.

Polyatomic Ion

Sulfate is considered a polyatomic anion. A polyatomic ion is a group of two or more atoms that behave as a single unit. Sulfate is an anion because its overall charge is negative. When sulfate is converted into sulfuric acid it is known to produce salt. Sulfates will often make bonds with cations to form neutral and more stable compounds such as aluminum sulfate {eq}Al_{2}(SO_{4})_{3} {/eq} and magnesium sulfate {eq}Mg(SO_{4} {/eq}.

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Common Minerals & Their Uses

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:00 What Is a Sulfate?
  • 1:38 Sulfate Structure
  • 3:24 Sulfate Formula
  • 4:32 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed Speed

Aluminum Sulfate

Image of Aluminum Sulfate

Magnesium Sulfate

Image of Magnesium Sulfate

Sulfate Structure

Both sulfur and oxygen are found in group VI of the periodic table. Elements in this group have 6 valence electrons. Valence electrons are electrons located in the outer shell of an atom. They are the electrons involved in bonding.

  • There are a total of 32 valence electrons in sulfate.
  • Sulfur has 6 valence electrons.
  • Each oxygen atom has 6 valence electrons. Since sulfate has 4 oxygen atoms, that equals 24 valence electrons.
  • Sulfate has a charge of {eq}2^{-} {/eq}, which means it has an additional 2 electrons.

When drawing the Lewis structure for sulfate, sulfur is placed in the center of the Lewis structure because it is the least electronegative atom. The remaining four oxygen atoms are placed around sulfur. There are two electrons shared between each sulfur and oxygen atom making four single bonds. The remaining 24 electrons are placed around the outer oxygen atoms. In this Lewis structure, the octet rule is obeyed. The octet rule states that atoms will gain or lose electrons in order to achieve 8 electrons in the outer shell.

The Lewis dot structure for sulfate is shown below.

Lewis Dot Structure for Sulfate

Image of Lewis dot structure for sulfur. A sulfur atom is in the center and four atoms of oxygen have a single bond to sulfur.  Each oxygen atom has 6 unshared electrons.

According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, sulfate has tetrahedral geometry. This is because sulfate has 4 atoms around the central atom and zero lone pairs of electrons around the central atom. The angle between each oxygen atom is 109.5 degrees.

Sulfate is a Tetrahedral Molecule

V S E P R chart showing different three-dimensional geometries of molecules

SO_{4} Charge

Resonance structures are a group of two or more Lewis structures that represent a single polyatomic species. Sulfate has six resonance structures. Notice the placement of atoms is the same, but the location of double bonds is different. Some Lewis structures do not show sulfate with double bonds. The resonance structure below also violates the octet rule. Not all oxygen and sulfur atoms have 8 electrons in their valence shell.

Sulfate Resonance

Image showing 6 resonance structure of sulfate

When drawing the Lewis structure for sulfate, the following image results. In this Lewis structure, there are only single bonds, and the octet rule is obeyed. However, both the octet rule and formal charge must be observed when drawing the correct Lewis structure.

Lewis Structure of Sulfate

Image of Lewis dot structure for sulfur. A sulfur atom is in the center and four atoms of oxygen have a single bond to sulfur.  Each oxygen atom has 6 unshared electrons.

Formal Charge

In order to understand why there are double bonds in the resonance structures, the formal charge of each atom can be observed. Formal charge is defined as a charge assigned to an atom in a molecule assuming electrons in that molecule are shared equally.

The formula for finding formal charge is:

Formal Charge = Valence Electrons - Nonbonding Valence Electrons - (Bonding Electrons/2)

The oxygen atom below labeled 1 has 6 valence electrons. This is because it is in group VI on the periodic table. There are 6 nonbonding electrons (circled in green) and 2 bonding electrons (circled in pink).

  • Formal Charge = 6 - 6 - (2/2) = -1
  • The remainder of oxygen atoms will have the same formal charge.

The sulfur atom below has 6 valence electrons. This is because sulfur is in group VI on the periodic table. There are 0 nonbonding electrons and 8 bonding electrons.

  • Formal Charge = 6 - 0 - (8/2) = +2

Lewis Structure of Sulfate

Image of Lewis dot structure for sulfur. A sulfur atom is in the center and four atoms of oxygen have a single bond to sulfur.  Each oxygen atom has 6 unshared electrons.

The image below shows the formal changes for each atom. Notice each atom has charges. When this happens, the molecule is unstable.

Formal Charges of Atoms in Sulfate

Image of Lewis dot structure for sulfur. A sulfur atom is in the center and four atoms of oxygen have a single bond to sulfur.  Each oxygen atom has 6 unshared electrons. The formal charge on each oxygen atom is negative 1.  Formal charge on a sulfur atom is plus 2.

In order to reduce charges on the atom, lone pairs can be converted to bonds. Since oxygen atoms are more electronegative than sulfur, oxygen atoms should hold negative charges. Notice how the conversion of lone pairs to a bond reduces charges making the molecule more stable.

Stable Resonance Structure of Sulfate

Image of Lewis dot structure for sulfur. A sulfur atom is in the center with a formal charge of zero. Two oxygen atoms have a single bond to sulfur, 6 unpaired electrons, and a formal charge of negative 1.  Two oxygen atoms have a double bond to sulfur, 4 unbonded electrons, and a formal charge of zero.

The six resonance structures of sulfate are a result of different combinations of these double bonds forming.

Charge on Sulfate

Sulfate has a {eq}2^{-} {/eq} charge. In order to understand why this polyatomic ion has a charge, the formal charge of one of the resonance structures can be observed.

In the image below, the oxygen atom labeled 1 has 6 valence electrons. This is because it is in group VI on the periodic table. There are 4 nonbonding electrons (circled in green) and 4 bonding electrons (circled in yellow).

  • Formal Charge = 6 - 4 - (4/2) = 0
  • The oxygen atom labeled 3 will have the same formal charge.

The oxygen atom labeled 2 has 6 valence electrons. This is because it is in group VI on the periodic table. There are 6 nonbonding electrons and 2 bonding electrons.

  • Formal Charge = 6 - 6 - (2/2) = -1
  • The oxygen atom labeled 4 will have the same formal charge.

The sulfur atom in the center has 6 valence electrons. This is because it is in group VI on the periodic table. There are 0 nonbonding electrons and 12 bonding electrons.

Formal Charge = 6 - 0 - (12/2) = 0

Stable Resonance Structure of Sulfate

Image of Lewis dot structure for sulfur. A sulfur atom is in the center.  Two oxygen atoms have a single bond to sulfur and 6 unpaired electrons.  Two oxygen atoms have a double bond to sulfur and 4 unbonded electrons.

To unlock this lesson you must be a Study.com Member.
Create your account

Frequently Asked Questions

What is sulfate in chemistry?

Sulfate is considered a polyatomic anion. A polyatomic ion is a group of two or more atoms that behave as a single unit. Sulfate is an anion because its overall charge is negative.

What is Sulfate made of?

Sulfate is a compound made of sulfur and oxygen. It is a polyatomic anion made of one sulfur atom and four oxygen atoms.

What is sulfate used for?

Organisms living near deep-sea thermal vents use sulfates as electron acceptors.

Magnesium sulfate is commonly known as Epsom salts. These salts are used in therapeutic baths. Gypsum is the natural mineral form of hydrated calcium sulfate, which is used to manufacture plaster. Chemicals found in cleaning agents (detergents, shampoo). Sodium lauryl sulfate and sodium laureth sulfate are the two main sulfates found in shampoo. These compounds create lathers removing oil and dirt.

It is also used in dietary supplements, breads, preserved fruits and vegetables, gelatins, and puddings

What is the formal charge of S in SO4?

The formal charge of sulfur in a sulfate compound is zero. This is due to its six different resonance structures.

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days