The key difference between halogens and pseudohalogens is that the halogens are group 17 elements in the periodic table whereas the pseudohalogens are combinations of different chemical elements that have the chemical characteristics of halogens.
The name halogen means “salt-producing”. Therefore, these chemical elements have the essential chemical characteristic of producing salts by forming anions. However, pseudohalogens are not halogens, but they have the chemical characteristics of halogens such as the formation of covalent compounds and complexes similar to halogens. Let us talk more details on these compounds.
CONTENTS
1. Overview and Key Difference
2. What are Halogens
3. What are Pseudohalogens
4. Similarities Between Halogens and Pseudohalogens
5. Side by Side Comparison – Halogens vs Pseudohalogens in Tabular Form
6. Summary
What are Halogens?
Halogens are chemical elements in the group 17 of the periodic table. It has five members; fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The general symbol that we use to refer to any halogen is “X”. The term halogen means, “salt-producing”. This is because these chemical elements can react with metals to form anions and produce a wide range of salts. This group of elements is the only group in the periodic table that has elements that exist in all three states of matter at standard temperature and pressure; fluorine and chlorine exist as gases, bromine exist as a liquid and iodine is a solid at room temperature. Moreover, these elements are highly reactive.
Figure 01: Halogens
They also easily form anions with -1 charge by obtaining one electron to their outermost orbital. This is because these elements have one unpaired electron in their outermost p orbital. Moreover, the compounds that these elements form include hydrogen halides, metal halides, interhalogen compounds (has two halogens), organohalogen compounds (halogens bonded to organic molecules), etc.
What are Pseudohalogens?
Pseudohalogens are chemical compounds having a combination of several chemical elements that shows the chemical characteristics of halogens. These are essentially polyatomic molecules. This means each pseudohalogen contains at least two atoms of different chemical elements. The chemistry of these compounds resembles the true halogens. Therefore, they can easily replace halogens by substituting them. These chemical components occur in the following forms.
- Pseudohalogen molecules; inorganic molecules:
- Symmetrical molecules such as cyanogen ((CN)2)
- Asymmetrical molecules such as BrCN
- Pseudohalide anions such as cyanide ion
- Inorganic acids such as HCN
- As ligands in coordination compounds such as ferricyanides
- As functional groups in organic molecules such as nitrile group.
The presence of single or double bonds do not affect the chemical behaviour of these compounds. Thus, they can act as chemical components that resemble halogens. They can form strong acids which resemble HX type halogenic acids (for example HCo(CO)4 resembles HCl). Moreover, they can react with metals to form compounds which resemble MX types halogenic compounds (foe example NaN3 resembles NaCl).
What are the Similarities Between Halogens and Pseudohalogens?
- Both chemical species have similar chemical behaviour
- Both Halogens and Pseudohalogenscan form strong acids
- Halogens and Pseudohalogens can react with metals to form salts
- Ionic species of both types carry a -1 electrical charge.
What is the Difference Between Halogens and Pseudohalogens?
Halogens are chemical elements in the group 17 of the periodic table. These are chemical elements. Moreover, these are very reactive chemical species which are well-known as “salt-producing” agents. Pseudohalogens are chemical compounds having a combination of several chemical elements which shows chemical characteristics of halogens. That is, unlike halogens, pseudohalogens are chemical compounds. In addition to that, they have a chemical behaviour that resembles halogens. The below infographic presents more details on the difference between halogens and pseudohalogens.
Summary – Halogens vs Pseudohalogens
Pseudohalogens are chemical species that resembles halogens. The difference between halogens and pseudohalogens is that the halogens are group 17 elements in the periodic table whereas the pseudohalogens are combinations of different chemical elements that have the chemical characteristics of halogens.
Reference:
1. “Halogen.” Wikipedia, Wikimedia Foundation, 10 July 2018. Available here
2. “Pseudohalogen.” Wikipedia, Wikimedia Foundation, 2 Mar. 2018. Available here
Image Courtesy:
1.’Halogene’By Tomihahndorf, (CC BY-SA 3.0) via Commons Wikimedia