Friday, January 25, 2019

WHAT IS AN ANION? - An anion is attracted to the anode in electrolysis. Anions are typically larger than cations (positively charged ions) because they have extra electrons around them. When naming a chemical compound, the cation is given first, followed by the anion. For example, the compound sodium chloride is written NaCl, where Na+ is the cation and Cl-is the anion. The net electrical charge of an anion is denoted using a superscript after the chemical species symbol. For example, the phosphate ion PO43- has a charge of 3-.

Ball-and-stick model of the bistriflimide anion
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What Is an Anion?
Anion Definition and Examples
Chemistry Basics: What Is an Anion?
by Anne Marie Helmenstine, Ph.D.


An anion is an ionic species having a negative charge.
The chemical species may be a single atom or a group of atoms.
An anion is attracted to the anode in electrolysis.
Anions are typically larger than cations (positively charged ions) because they have extra electrons around them.
The word anion [an-ahy-uh n] was proposed by English polymath Rev. William Whewell in 1834, from Greek anion "thing going up", referring to the movement of anions during electrolysis.
Physicist Michael Faraday was the first person to use the term anion in a publication.

Anion Examples

·       Free chloride in an aqueous table salt (NaCl) solution: Cl-
·       Singlet oxygen: O-
·       Superoxide: O2-
·       Hydroxide ion: OH-
·       Sulfate: SO42-
·       Al(OH)4-

Anion Notation

When naming a chemical compound, the cation is given first, followed by the anion. For example, the compound sodium chloride is written NaCl, where Na+ is the cation and Cl-is the anion.
The net electrical charge of an anion is denoted using a superscript after the chemical species symbol. For example, the phosphate ion PO43- has a charge of 3-.
Since many elements display a range of valences, determining the anion and cation in a chemical formula isn't always clearcut.
In general, the difference in electronegativity may be used to identify the cation and anion in a formula.
The more electronegative species in a chemical bond is the anion. 

Table of Common Anions

Simple Anions
Formula
Hydride
H-
Oxide
O2-
Fluoride
F-
Sulfide
S2-
Chloride
Cl-
Nitride
N3-
Bromide
Br-
Iodide
I-


Oxoanions
Formula
Arsenate
AsO43-
Phosphate
PO43-
Arsenite
AsO33-
Hydrogen Phosphate
HPO42-
Dihydrogen Phosphate
H2PO4-
Sulfate
SO42-
Nitrate
NO3-
Hydrogen Sulfate
HSO4-
Nitrite
NO2-
Thiosulfate
S2O32-
Sulfite
SO32-
Perchlorate
ClO4-
Iodate
IO3-
Chlorate
ClO3-
Bromate
BrO3-
Chlorite
ClO2-
Hypochlorite
OCl-
Hypobromite
OBr-
Carbonate
CO32-
Chromate
CrO42-
Hydrogen Carbonate or Bicarbonate
HCO3-
Dichromate
Cr2O72-


Anions from Organic Acids
Formula
Acetate
CH3COO-
Formate
HCOO-


Other Anions
Formula
Cyanide
CN-
Amide
NH2-
Cyanate
OCN-
Peroxide
O22-
Thiocyanate
SCN-
Oxalate
C2O42-
Hydroxide
OH-
Permanganate
MnO4-

Anne Marie Helmenstine, Ph.D.
·   Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.
·   Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.
·   ThoughtCo and About Education chemistry expert since 2001.
·   Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.
Experience
Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.
In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 
Education
Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.
Anne Marie Helmenstine, Ph.D.​
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Ball-and-stick model of the bistriflimide anion



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