The average bond order is defined as the average number of chemical bonds between a pair of elements. In this context, a single bond is assigned a bond order of 1, a double bond has a bond order of 2, and a triple bond carries a bond order of 3. Understanding bond order is crucial because it directly influences the properties of the bond. As the average bond order increases, the strength of the bond also increases, while the length of the bond decreases. This relationship indicates that average bond order and bond strength are directly proportional, meaning that stronger bonds tend to be shorter. This concept is essential for predicting the behavior of molecules in chemical reactions and understanding their stability.
11. Bonding & Molecular Structure
Average Bond Order
11. Bonding & Molecular Structure
Average Bond Order: 동영상 및 연습문제
주제 요약
Average Bond Order is the average number of chemical bonds between a pair of elements, especially in species with resonance. A single bond has a bond order of 1, a double bond has a bond order of 2, and a triple bond has a bond order of 3. In resonance structures, a localized \(\pi\) bond is not confined to one atom pair, so the bonding is shared across equivalent surrounding atoms.
To find the bond order, count the total number of bonds between the central atom and the relevant surrounding atoms, then divide by the number of those surrounding atoms: \( \text{Average bond order}=\frac{\text{total number of bonds}}{\text{number of surrounding atoms}} \) . As average bond order increases, bond strength increases and bond length decreases. This helps explain why equivalent bonds in resonance hybrids are intermediate between pure single and double bonds.
Average Bond Order represents the average number of chemical bonds between a pair of bond elements.
Average Bond Order
0
개념
Average Bond Order
영상 길이:
36sAverage Bond Order Video Summary
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A single bond has a bond order of 1, a double bond has a bond order of 2, and a triple bond has a bond of 3.
Larger the Average Bond Order, stronger the bond strength and shorter the length of the bond.
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예시
Average Bond Order Example 1
영상 길이:
2mAverage Bond Order Example 1 Video Summary
To determine the average bond order of the sulfur-oxygen bonds within the sulfite ion (SO32-), we start by analyzing its resonance structures. In one common resonance structure, sulfur is double bonded to one oxygen atom and single bonded to the other two oxygen atoms. This configuration allows us to visualize the distribution of bonds among the surrounding elements.
First, we count the total number of bonds between sulfur and oxygen. In this case, there are four bonds: one double bond (counted as two) and two single bonds (counted as one each). Therefore, the total number of bonds is:
2 (from the double bond) + 1 + 1 (from the two single bonds) = 4 bonds.
Next, we identify the number of surrounding elements, which in this case are the three oxygen atoms. To find the average bond order, we divide the total number of bonds by the number of surrounding elements:
Average bond order = Total bonds / Number of surrounding elements = 4 / 3 = 1.33.
This average bond order of 1.33 indicates that while each oxygen atom is single bonded to sulfur, the presence of resonance allows for the sharing of a pi bond among the three oxygen atoms. Thus, each oxygen effectively has a third of that pi bond, leading to the fractional bond order. This method of calculating average bond order can be applied to other molecules by counting the total bonds and dividing by the number of surrounding atoms involved.
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문제
What is the bond order of the phosphate–oxygen bonds within the phosphate ion, PO43–?
A
1.25
B
2
C
2.5
D
1
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11. Bonding & Molecular Structure
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11. Bonding & Molecular Structure - Part 1 of 4
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Average bond order is defined as the average number of chemical bonds between a pair of atoms, especially in molecules or ions that exhibit resonance. In simple terms, it represents how many bonds, on average, exist between two atoms. For example, a single bond has a bond order of 1, a double bond has a bond order of 2, and a triple bond has a bond order of 3. In molecules with resonance, the bonding electrons are delocalized, so the bond order can be fractional, reflecting the shared bonding across multiple atoms. This concept helps explain the bond strength and bond length in such molecules.
To calculate the average bond order in a molecule with resonance, first count the total number of bonds between the central atom and the surrounding equivalent atoms across all resonance structures. Then, divide this total by the number of those surrounding atoms. Mathematically, this is expressed as: . This calculation gives a fractional bond order that reflects the delocalized bonding in resonance structures.
The average bond order is directly related to both bond strength and bond length. As the average bond order increases, the bond strength also increases because more bonding interactions hold the atoms together more tightly. Conversely, the bond length decreases with increasing bond order because stronger bonds pull the atoms closer. For example, a triple bond (bond order 3) is stronger and shorter than a double bond (bond order 2), which in turn is stronger and shorter than a single bond (bond order 1). This relationship helps explain the physical properties of molecules based on their bonding.
Resonance structures represent different possible arrangements of electrons in a molecule where the bonding electrons are delocalized over multiple atoms. Because the actual molecule is a hybrid of these resonance forms, the bonds are not purely single or double but share characteristics of both. This delocalization causes the bond order to be averaged over the resonance structures, resulting in fractional bond orders. For example, in the nitrate ion (NO3−), the bonds between nitrogen and oxygen are equivalent and have a bond order of approximately 1.33, reflecting the shared double bond character distributed among three N–O bonds.
Average bond order is a useful indicator of molecular stability because it reflects the strength and nature of bonding between atoms. Higher average bond orders generally correspond to stronger bonds, which contribute to greater molecular stability. In molecules with resonance, fractional bond orders indicate delocalized bonding, which often stabilizes the molecule by distributing electron density more evenly. Therefore, analyzing average bond order helps predict how stable a molecule or ion is, based on the bonding interactions present.
