The key difference between polyatomic ions and compounds is that the polyatomic ions have either a positive or negative electrical charge whereas the compounds have no net electrical charge.
A polyatomic ion is a term that we use to name chemical species containing two or more atoms that have a net negative or positive electrical charge. The electrical charge of this ion is a result of the number of electrons present in each atom; if there are more electrons than the total number of protons in atoms, it gets a net negative charge and vice versa. Compounds, on the other hand, are chemical species with no electrical charge. They have equal numbers of electrons and protons.
CONTENTS
1. Overview and Key Difference
2. What are Polyatomic Ions
3. What are Compounds
4. Side by Side Comparison – Polyatomic Ions vs Compounds in Tabular Form
5. Summary
What are Polyatomic Ions?
Polyatomic ions are chemical species having two or more atoms and a net electrical charge. This electrical charge can be either a positive charge or a negative charge depending on the number of electrons and protons present in the chemical species. A synonym for this species is “molecular ion”. The atoms bind with each other covalently. We can consider some metal complexes as polyatomic ions if they act as a single unit. In contrast, monoatomic ions are single atoms, which carry an electrical charge. We can find these ions in salt compounds, coordination compounds, and many other ionic compounds; as a part of the compound.
Figure 01: A Nitrate Ion
Some examples of polyatomic ions:
- Acetate ion (CH3COO–)
- Benzoate ion (C6H5COO–)
- Carbonate ion (CO32–)
- Cyanide ion (CN–)
- Hydroxide ion (OH–)
- Nitrite ion (NO2–)
- Ammonium ion (NH4+)
What are Compounds?
Compounds are chemical species containing identical molecules consist of atoms of two or more chemical elements. Therefore, these chemical species do not carry a net electrical charge. Therefore, they are neutral species. The atoms bind with each other via either covalent bonds, coordination bonds, or ionic bonds. Moreover, if there is a molecule containing two or more atoms of the same element bonded to each other, it is not a compound since there are no different elements.
Figure 02: A Water Molecule
Moreover, according to the definition, there are 4 types of compounds as follows:
- Molecules having combinations of different chemical elements
- Ionic compounds consist of ionic bonds
- Intermetallic compounds having metallic bonds
- Coordination complexes consist of coordinate bonds
We can use a chemical formula in order to express the chemical elements and the ratio between them present in a compound. For example, the chemical formula of the water molecule is H2O. It has two hydrogen atoms and one oxygen atom, but the molecule has no net electrical charge; thus it is a chemical compound.
What is the Difference Between Polyatomic Ions and Compounds?
Polyatomic ions are chemical species having two or more atoms and a net electrical charge. They have either a positive or negative electrical charge. Compounds are chemical species containing identical molecules consist of atoms of two or more chemical elements. They have no net electrical charge. This is the key difference between polyatomic ions and compounds. Moreover, polyatomic ions have either covalent bonds or coordination bonds between the atoms. Whereas, compounds may have covalent bonds, ionic bonds, metallic bonds or coordination bonds between atoms.
The below infographic presents the difference between polyatomic ions and compounds in tabular form.
Summary – Polyatomic Ions vs Compounds
The key difference between polyatomic ions and compounds is that polyatomic ions have either a positive or negative electrical charge whereas compounds have no net electrical charge. This is mainly because polyatomic ions have an imbalanced number of electrons and protons while compounds have equal numbers of electron and protons.
Reference:
1. Helmenstine, Anne Marie, Ph.D. “Polyatomic Ion Definition and Examples.” ThoughtCo, Jun. 22, 2018. Available here
2. Noller, Carl R., et al. “Chemical Compound.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 6 Dec. 2016. Available here
Image Courtesy:
1.”Nitrate-ion-elpot”By Benjah-bmm27 – Own work, (Public Domain) via Commons Wikimedia
2.”Water-3D-balls”By Benjah-bmm27 – Own work, (Public Domain) via Commons Wikimedia