Learning Materials
Features
Discover
Many substances are made up of just two types of ions—a metal cation and a nonmetal anion. Each ion is made up of only one type of atom. There are other ways that atoms can join together, either as larger ionic complexes or as full molecules. Polyatomic ions are found in some of the most useful things we work with. So, what are polyatomic ions? Keep reading to find out!
Millions of flashcards designed to help you ace your studies
Sign up for freeTrue or False: Polyatomic ions dissociate in water
True or False: Polyatomic ions can form compounds with each other
What is the name of the following compound?Al2(SO4)3
What is the name of the following compound?NI3
True or False: FeO3H3 is a valid way to write a compound containing Fe3+ and 3OH- ions.
What is the name of this polyatomic ions?NO3-
What is the name of this polyatomic ion?NH4+
What is the naming convention for polyatomic ions?
What is the charge of the hydroxide (OH?) ion?
A __ is an ion with a positive charge, while a ___ is an ion with a negative charge
What is the name of this polyatomic ion?NH4+
What is the naming convention for polyatomic ions?
What is the charge of the hydroxide (OH?) ion?
A __ is an ion with a positive charge, while a ___ is an ion with a negative charge
True or False: Polyatomic ions dissociate in water
True or False: Polyatomic ions can form compounds with each other
What is the name of the following compound?Al2(SO4)3
What is the name of the following compound?NI3
True or False: FeO3H3 is a valid way to write a compound containing Fe3+ and 3OH- ions.
What is the name of this polyatomic ions?NO3-
Achieve better grades quicker with Premium
Geld-zurück-Garantie, wenn du durch die Prüfung fällst
Did you know that StudySmarter supports you beyond learning?
Review generated flashcards
Start learning or create your own AI flashcards
Team Polyatomic Ions Teachers
Thank you for your interest in audio learning!
This feature isn’t ready just yet, but we’d love to hear why you prefer audio learning.
Why do you prefer audio learning? (optional)
Send FeedbackA polyatomic ion is a group of two or more covalently bonded atoms (or a metal complex), that acts like a single unit and has a net charge.
Depending on the definition used, the word "molecule" may or may not be used to describe an ion with more than one atom. The Greek prefix poly- means "many," but even ions with only two atoms are often called "polyatomic."
These ions essentially act as one, (mostly) inseparable unit. So what do I mean by that? Well, let's talk about dissociation.
When compounds that are soluble in water are placed in water, they will dissociate (i.e., break apart). For example, here is the dissociation for NaCl:
Basically, the compound is breaking down into its ions. Now, what about a compound containing a polyatomic ion? Let's look at the dissociation of sulfuric acid (H2SO4), which contains the polyatomic ion sulfate (SO42-)
As you can see, the sulfate ion stays intact, this is what I meant by "inseparable".
Now that we have a general idea of what a polyatomic ion is, let's look at some examples.
Here's calcium carbonate (CaCO3), which contains the polyatomic ion carbonate (CO32-):
Fig.1-Calcium carbonate (CaCO3)
Here we see that carbonate acts as one unit with a -2 charge. The calcium ion (Ca2+) is attracted to this charge and forms a bond with the polyatomic ions.
The dashed lines on carbonate show that each double bond is really a "1 1/3 bond". Carbonate has several resonance forms, where each C-O bond can be a C=O bond.
Polyatomic ions can form compounds with each other, as shown below with ammonium carbonate ((NH4)2CO3):
Fig.2-Structure of ammonium carbonate ((NH4)2CO3)
Each ammonium ion (NH4+) has a +1 charge, while carbonate, as we saw earlier, has a -2 charge. Each ammonium ion bonds to one side of the carbonate ion.
Ionic compounds with polyatomic ions are named the same way as other ionic compounds: just put the name of the cation and the name of the anion together. If there is more than one polyatomic ion, don't add a number to the name. The only time this is okay is if the name of the ion already has a number in it, like dichromate or triiodide.
For example, H2SO3 is hydrogen sulfate.
There is one important difference in how the formulas for ionic compounds are written. If more than one polyatomic ion is needed to balance the overall charge in the formula, put the formula of the polyatomic ion in parentheses and write the correct numerical subscript to the right of the parentheses. So, the right way to write the formula for the beryllium ion (Be2+) and the hydroxide ion (OH-) is Be(OH)2, not BeOH2 or BeO2H2. When they are needed, use parentheses. This ionic compound is called "beryllium hydroxide," which is its only name.
There are plenty of polyatomic ions, but there are some that you will encounter a lot in your chemistry career. Since polyatomic ions are considered one unit and not a compound, they do not follow the naming convention for compounds. Instead, we just memorize the names and charges.
While this may seem like a daunting task at first, you'll get the hang of it eventually!
Below is a chart showing some common polyatomic ions:
Fig.3-A list of common polyatomic ions in order of charge
You'll notice that some of these ions, like nitrate (NO3-) and nitrite (NO2-) look very similar. This type of ion is called an oxyanion since it contains oxygen and is an anion (negatively charged ion).
When we name these ions, the suffix is based on the number of oxygen:
This convention is based on the number of possible oxygen atoms, as shown below:
Fig.4-Chart for naming oxyanions
Polyatomic ions can have a wide variety of charges. Negatively charged species (anions) are much more common, however, there are still some that have positive charges (cations).
So where do these charges come from? These charges are based on the component element's Oxidation Number.
A species' Oxidation Number is the theoretical charge it will have during Bonding. This number tells us how many electrons the species will lose (positive number) or gain (negative number) during bonding.
Fig.5-Chart with common oxidation states
Now that we know what oxidation states are, let's look at how to determine the charge of a polyatomic ion.Find the charge of the polyatomic ion carbonate (CO3?)
Oxygen commonly has an oxidation state of -2. Generally speaking, the species on the left has a positive charge, while the species on the right have a negative charge. Because of this, Carbon's oxidation state is +4 here instead of -4.
Adding these, we get,
Therefore, the charge on carbonate is -2.
Sign up for free to gain access to all our flashcards.
What are polyatomic ions?
A polyatomic ion is a group of two or more covalently bonded atoms (or a metal complex), that acts like a single unit and has a net charge
Are polyatomic ions metals?
While some polyatomic ions can contain metals, most common polyatomic ions are made of only nonmetals
How to name ionic compounds with polyatomic ions?
Ionic compounds with polyatomic ions are named the same way as other ionic compounds: just put the name of the cation and the name of the anion together. If there is more than one polyatomic ion, don't add a number to the name.
What polyatomic ions have a -2 charge?
Some polyatomic ions with a -2 charge include:
Do polyatomic ions dissociate when they dissolve in water, or do they remain intact?
Polyatomic ions do not dissociate in water, instead, they remain intact.
At StudySmarter, we have created a learning platform that serves millions of students. Meet the people who work hard to deliver fact based content as well as making sure it is verified.
Lily Hulatt is a Digital Content Specialist with over three years of experience in content strategy and curriculum design. She gained her PhD in English Literature from Durham University in 2022, taught in Durham University’s English Studies Department, and has contributed to a number of publications. Lily specialises in English Literature, English Language, History, and Philosophy.
Get to know Lily
Gabriel Freitas is an AI Engineer with a solid experience in software development, machine learning algorithms, and generative AI, including large language models’ (LLMs) applications. Graduated in Electrical Engineering at the University of São Paulo, he is currently pursuing an MSc in Computer Engineering at the University of Campinas, specializing in machine learning topics. Gabriel has a strong background in software engineering and has worked on projects involving computer vision, embedded AI, and LLM applications.
Get to know Gabriel
StudySmarter is a globally recognized educational technology company, offering a holistic learning platform designed for students of all ages and educational levels. Our platform provides learning support for a wide range of subjects, including STEM, Social Sciences, and Languages and also helps students to successfully master various tests and exams worldwide, such as GCSE, A Level, SAT, ACT, Abitur, and more. We offer an extensive library of learning materials, including interactive flashcards, comprehensive textbook solutions, and detailed explanations. The cutting-edge technology and tools we provide help students create their own learning materials. StudySmarter’s content is not only expert-verified but also regularly updated to ensure accuracy and relevance.
Learn moreSave explanations to your personalised space and access them anytime, anywhere!
By signing up, you agree to the Terms and Conditions and the Privacy Policy of StudySmarter.
Already have an account? Log in
Sign up to highlight and take notes. It’s 100% free.
The first learning app that truly has everything you need to ace your exams in one place
The first learning platform with all the tools and study materials you need.
Explanations 
Flashcards 
StudySmarter AI 
Notes 
Study Plans 
Study Sets 
Exams 
Find a job 
Student Deals 
Magazine 
Mobile App 
