Chem Explorers

Understanding Bond Order in Chemistry: Definition Calculation and Examples

Understanding Bond Order: Definition and Examples

In the world of chemistry, bond order is an essential concept that helps explain the type of bond between two atoms in a molecule. Bond order is a quantitative measure of the number of chemical bonds formed between two atoms in a molecule.

In simpler terms, bond order is the number of electron pairs shared between two atoms in a molecule. In this article, we’ll be delving into bond order, what it means, and how to calculate it.

We’ll explore different types of molecules and their bond orders to give you a clear understanding of this crucial chemical concept. What is Bond Order?

Bond order is a numerical value that represents the stability of a chemical bond between two atoms present in a molecule. It determines the bond strength, bond length, and bond energy of the molecule.

A molecule’s bond order is calculated based on the number of chemical bonds in the molecular structure. Let’s take the example of oxygen (O2) to understand bond order.

Oxygen has two atoms in its molecular structure that are bonded together. The bond order of oxygen is two because two electrons pairs are shared between two oxygen atoms, forming a stable oxygen molecule (O2).

In other words, bond order tells us the number of bonds between two atoms. If two atoms share one electron pair, the bond order is one.

If two atoms share two electron pairs, the bond order is two. If two atoms share three electron pairs, the bond order is three.

The higher the bond order, the stronger the chemical bond between the atoms in the molecule.

Examples of Bond Order

Now let’s look at some examples of molecules and their bond orders:

Hydrogen: Hydrogen has just one atom in its molecule, so it doesn’t have a bond order. Oxygen: Oxygen has two atoms in its molecule, and they share two electron pairs.

Therefore, the bond order of oxygen is two. Nitrogen: Nitrogen has two atoms in its molecule, and they share three electron pairs.

Therefore, the bond order of nitrogen is three.

Determining Bond Order Using Lewis Structure

The Lewis structure is a diagram used to represent the electron distribution in a molecule. By drawing a Lewis structure, we can determine the number of valence electrons in a molecule and how these electrons are distributed among atoms in the molecule.

To determine bond order using the Lewis structure, we follow the steps outlined below:

Step 1: Draw the Lewis structure of the molecule

The first step is to determine the Lewis structure of the molecule in question. Step 2: Count the total number of valence electrons

The next step is to count the total number of valence electrons of atoms in the molecule.

Step 3: Determine the number of electrons pairs shared between the atoms

The next step is to determine the number of electron pairs shared between the atoms in the molecule. Step 4: Calculate the bond order

Finally, use the number of electron pairs shared between two atoms to calculate the bond order.

Examples of Calculating Bond Order Using Lewis Structure

Let’s walk through some examples to show how to calculate bond order using the Lewis structure. Nitrate Ion (NO3-):

Step 1: Draw the Lewis structure of the molecule

The Lewis structure of nitrate ion can be represented as:

O

//

O=N+=O or O–N–O

\

O

Step 2: Count the total number of valence electrons

The total number of valence electrons in nitrate ion is 24 (5 from nitrogen atom + 6 from each oxygen atom – 1 for the negative charge).

Step 3: Determine the number of electrons pairs shared between atoms

In nitrate ion, nitrogen atom shares three electron pairs with three oxygen atoms. Therefore, the bond order between nitrogen and oxygen is three.

Step 4: Calculate the bond order

To calculate the bond order in nitrate ion, we need to sum up the bond orders between nitrogen and oxygen atoms and divide by the total number of bonds:

((3 bonds * 3 pairs) + (1 bond * 1 pair)) / 4 = 2.25

Therefore, the bond order of the nitrogen-oxygen bond in nitrate ion is 2.25. Ethylene (C2H4):

Step 1: Draw the Lewis structure of the molecule

The Lewis structure of ethylene can be represented as:

H H

| |

H — C = C — H

Step 2: Count the total number of valence electrons

The total number of valence electrons in ethylene is 12 (2 from each carbon atom + 1 from each hydrogen atom).

Step 3: Determine the number of electrons pairs shared between atoms

In ethylene, each carbon atom shares one electron pair with the other carbon atom and one electron pair with one hydrogen atom. Therefore, the bond order in each carbon-carbon bond is two, and the bond order between each carbon atom and the hydrogen atom is one.

Step 4: Calculate the bond order

To calculate the bond order in ethylene, we need to sum up the bond orders between carbon and carbon atoms and divide by the total number of bonds:

((2 bonds * 2 pairs) / 2) = 2

Therefore, the bond order of the carbon-carbon bond in ethylene is two. Sulfur Dioxide (SO2):

Step 1: Draw the Lewis structure of the molecule

The Lewis structure of sulfur dioxide can be represented as:

O

//

S = O

\

O

Step 2: Count the total number of valence electrons

The total number of valence electrons in sulfur dioxide is 18 (6 from sulfur atom + 6 from two oxygen atoms).

Step 3: Determine the number of electrons pairs shared between atoms

In sulfur dioxide, sulfur atom shares one electron pair with each oxygen atom. Therefore, the bond order between sulfur and each oxygen atom is one.

Step 4: Calculate the bond order

To calculate the bond order in sulfur dioxide, we need to sum up the bond orders between sulfur and oxygen atoms and divide by the total number of bonds:

((1 bond * 2 pairs)) / 2 = 1

Therefore, the bond order of the sulfur-oxygen bond in sulfur dioxide is one. Ozone (O3):

Step 1: Draw the Lewis structure of the molecule

The Lewis structure of ozone can be represented as:

O

//

O = O

\

O

Step 2: Count the total number of valence electrons

The total number of valence electrons in ozone is 18 (6 from each oxygen atom).

Step 3: Determine the number of electrons pairs shared between atoms

In ozone, each oxygen atom shares one electron pair with the other oxygen atom. Therefore, the bond order in each oxygen-oxygen bond is one.

Step 4: Calculate the bond order

To calculate the bond order in ozone, we need to sum up the bond orders between oxygen atoms and divide by the total number of bonds:

((1 bond * 3 pairs) / 2) = 1.5

Therefore, the bond order of the oxygen-oxygen bond in ozone is 1.5.

Conclusion

In conclusion, bond order is a crucial concept in chemistry that determines the bond strength and bond length of a molecule. Bond order can be calculated using a Lewis structure, which represents the electron distribution in a molecule.

By understanding bond order, we can determine the type of bond between two atoms in a molecule and gain insights into its chemical properties. With the examples provided in this article, we hope that you now have a good understanding of bond order.

Determining Bond Order Using Molecular Orbital Theory

Another way to determine bond order is through the use of molecular orbital theory. Unlike Lewis structure, which primarily focuses on the electron pairs present in a molecule, molecular orbital theory describes the molecular properties in terms of their constituent atomic orbitals.

Within molecular orbital theory, electrons are distributed in molecular orbitals, which are often formed by the overlap of atomic orbitals of different atoms.

Application of Molecular Orbital Theory to Determine Bond Order

Molecular orbital theory can be applied to calculate the bond order of a molecule. When two atomic orbitals, usually one from each atom, combine to form a molecular orbital, it can have one of three types of energy: bonding, antibonding, or non-bonding.

The bonding orbitals have lower energy than the atomic orbitals, and electrons residing in these orbitals stabilize the molecule by holding the two atoms together. Antibonding orbitals are formed in a similar way but their energies are higher than the constituent atomic orbitals.

Electrons occupying antibonding orbitals destabilize the molecule since they tend to push the atoms away from each other. In contrast, non-bonding orbitals have similar energies to the constituent atomic orbitals and do not contribute to the bond order.

Bond order can be calculated by subtracting the number of electrons in antibonding orbitals from the number of electrons in bonding orbitals and dividing the result by two.

Examples of Calculating Bond Order Using Molecular Orbital Theory

Let’s look at some examples to demonstrate how to calculate bond order using molecular orbital theory. Carbon Monoxide (CO):

Carbon monoxide is a linear molecule made up of carbon and oxygen atoms.

Each atom has two valence electrons. In molecular orbital theory, two different molecular orbitals are formed; bonding () and antibonding (*) orbitals.

Using molecular orbitals, we can write:

Both the carbon and oxygen atoms have two atomic orbitals each contributing to the and * orbitals respectively. In the bond there are two electrons present while in the * bond, there are only two electrons on oxygen where carbon has no electrons.

There are a total of four valence electrons contributing to the bonding orbitals, and two valence electrons contributing to antibonding orbitals. The bond order of CO is given by:

(4-2) / 2 = 1.

Nitrosonium (NO+):

Nitrosonium is a cation which is formed when an oxygen molecule binds to a nitrogen molecule. Nitrosonium, therefore, has two atoms, nitrogen, and oxygen.

Each atom has five and six valence electrons respectively. In molecular orbital theory, two different molecular orbitals are formed: bonding () and antibonding (*) orbitals.

Using molecular orbitals, we can write:

Both the nitrogen and oxygen atoms contribute to the molecular orbitals. In the bonding orbital, there are eight electrons present while in the antibonding orbital, there are only four electrons residing on oxygen.

The sum of valence electrons in bonding orbitals is sixteen while those of antibonding orbitals is four. The bond order of NO+ is given by:

(16-4) / 2 = 6.

Bond Order for Various Chemical Species

Comparison of Bond Orders for Different Chemical Species

Bond order can vary from molecule to molecule, and this is attributed to the difference in the strength of the electrostatic attraction between atoms. Let us consider different chemical species and compare their bond orders.

Dicarbon (C2):

Dicarbon is a linear molecule where two carbon atoms are bonded by a triple bond. Each carbon atom has four valence electrons.

Using molecular orbital theory, we can infer that there are three bonding orbitals and three antibonding orbitals. The bonding orbitals have a total of four electrons present, while the antibonding orbitals have a total of two electrons.

The bond order of dicarbon is given by:

(4-2) / 2 = 1. Diboron (B2):

Diboron is also a linear molecule where two boron atoms are bonded by a triple bond.

Each boron atom has three valence electrons. In molecular orbital theory, three bonding orbitals and three antibonding orbitals are formed.

Only the outermost electron pair resides in the bonding orbital. The bond order of diboron is given by:

(2-1) / 2 = 0.5.

Dilithium (Li2):

Dilithium is a linear molecule where two lithium atoms are bonded by a single bond.

Each lithium atom has one valence electron. In molecular orbital theory, one bonding orbital and one antibonding orbital are formed.

The bond order of dilithium is given by:

(2-0) / 2 = 1. Cyanide (CN-):

Cyanide is a molecular ion comprising of a nitrogen atom and a carbon atom.

Each atom in the molecule has five and four valence electrons respectively. Using the molecular orbital theory, four bonding orbitals and four antibonding orbitals are formed.

In total, the bonding orbitals have ten electrons present while the antibonding orbitals have six electrons. The bond order of cyanide is given by:

(10-6) / 2 = 2.

Table of Bond Orders for Select Chemical Species

The following table shows the bond orders of some select chemical species:

| Chemical Species | Bond Order |

|——————|————|

| Hydrogen (H2) | 1 |

| Oxygen (O2) | 2 |

| Fluorine (F2) | 1 |

| Diberyllium (Be2) | 0 |

| Nitrogen (N2) | 3 |

| Carbon Monoxide (CO) | 1 |

| Nitrosonium (NO+) | 6 |

| Cyanide (CN-) | 2 |

In summary, bond order is an essential concept in chemistry that helps determine the strength of the bond between atoms in a molecule. It becomes increasingly relevant when discussing the reactivity of a molecule.

Bond order can be calculated using either the Lewis structure or the molecular orbital theory approach. By comparing the bond orders of different chemical species, we can gain insights into their respective chemical properties.

In conclusion, understanding bond order is crucial in chemistry as it helps determine the strength and stability of chemical bonds in a molecule. Bond order can be calculated using either the Lewis structure or molecular orbital theory approaches.

The number of electron pairs shared between atoms determines the bond order, with higher values indicating stronger bonds. Through examples such as carbon monoxide and nitrosonium, we have seen how bond order calculations highlight the varying bond strengths in different molecules.

By comparing bond orders, chemists can predict the reactivity and properties of different chemical species. Overall, bond order is an important concept that provides valuable insights into molecular behavior and facilitates a deeper understanding of chemical structures.

FAQs:

1. What is bond order?

Bond order is a numerical value that represents the stability and strength of a chemical bond between two atoms in a molecule. 2.

How do you calculate bond order using Lewis structure? To calculate bond order using Lewis structure, you count the number of electron pairs shared between atoms and divide it by the total number of bonds in the molecule.

3. How does molecular orbital theory determine bond order?

Molecular orbital theory analyzes the distribution of electrons in molecular orbitals to determine bond order by subtracting the number of electrons in antibonding orbitals from those in bonding orbitals. 4.

What does a higher bond order indicate? A higher bond order indicates a stronger bond between atoms in a molecule.

5. How does bond order affect the properties of a molecule?

Bond order affects the length and strength of a bond, which in turn influence the reactivity and properties of a molecule. 6.

Can bond order be fractional? Yes, bond order can be fractional, indicating partial bonds or resonance structures in a molecule.

7. What can bond order help chemists predict?

Bond order can help chemists predict the stability, reactivity, and properties of different chemical species based on the strength and nature of their bonds.

Popular Posts