Bond Properties (9.4.1) Flashcards
• The greater the bond order, the shorter the bond length, and the greater the bond strength.
• The greater the bond order, the shorter the bond length, and the greater the bond strength.
• Bond orders which are not integers indicate molecules with resonance structures.
• Bond orders which are not integers indicate molecules with resonance structures.
• The difference in electronegativities between bonding atoms indicates the degree of ionic or covalent character in the bond.
• The difference in electronegativities between bonding atoms indicates the degree of ionic or covalent character in the bond.
Bond order describes the number of bonds between
bonding atoms. The greater the bond order, the
shorter the bond length.
For example, a single bond (bond order = 1) between carbon (C) and oxygen (O) is 143 picometers long, while a double bond (bond order = 2) between carbon and oxygen is 122 picometers long, and a triple bond (bond order = 3) between carbon and oxygen is 113 picometers long.
Bond order describes the number of bonds between
bonding atoms. The greater the bond order, the
shorter the bond length.
For example, a single bond (bond order = 1) between carbon (C) and oxygen (O) is 143 picometers long, while a double bond (bond order = 2) between carbon and oxygen is 122 picometers long, and a triple bond (bond order = 3) between carbon and oxygen is 113 picometers long.
Bond dissociation energy (BDE) is the amount of
energy required to homolytically break a bond in a
molecule that is in the gaseous state. Higher bond
dissociation energies indicate stronger bonds. The
greater the bond order, the greater the bond
strength, and therefore the higher the bond
dissociation energy.
For example, for a single bond (bond order = 1)
between carbon and oxygen, BDE = 358 kJ/mol.
For a double bond (bond order = 2) between carbon
and oxygen, BDE = 732 kJ/mol, and for a triple bond
(bond order = 3) between carbon and oxygen,
BDE = 1072 kJ/mol.
Bond dissociation energy (BDE) is the amount of
energy required to homolytically break a bond in a
molecule that is in the gaseous state. Higher bond
dissociation energies indicate stronger bonds. The
greater the bond order, the greater the bond
strength, and therefore the higher the bond
dissociation energy.
For example, for a single bond (bond order = 1)
between carbon and oxygen, BDE = 358 kJ/mol.
For a double bond (bond order = 2) between carbon
and oxygen, BDE = 732 kJ/mol, and for a triple bond
(bond order = 3) between carbon and oxygen,
BDE = 1072 kJ/mol.
Bond orders which are not integers indicate
molecules with resonance structures. The average
bond order is the sum of the bond orders of a given
bond in each resonance structure divided by the
number of resonance structures.
For example, in the carbonate ion (CO3
2–), the average bond order for the bond between the
central carbon atom and the oxygen atom on the
right is (2 + 1 + 1) / 3 = 1 1/3. The average bond
order for the other two carbon-oxygen bonds is also
1 1/3.
Bond orders which are not integers indicate
molecules with resonance structures. The average
bond order is the sum of the bond orders of a given
bond in each resonance structure divided by the
number of resonance structures.
For example, in the carbonate ion (CO3
2–), the average bond order for the bond between the
central carbon atom and the oxygen atom on the
right is (2 + 1 + 1) / 3 = 1 1/3. The average bond
order for the other two carbon-oxygen bonds is also
1 1/3.
The difference in electronegativities (∆EN) between
bonding atoms indicates the degree of ionic or
covalent character in the bond. If the difference in
electronegativities is larger than about 1.7, the bond
is said to be ionic. If the difference in
electronegativities is near zero, the bond is said to
be nonpolar covalent. If the difference in
electronegativities is greater than about 0.5 but less
than 1.7, the bond is said to be polar covalent.
For example, the difference in electronegativities
between lithium and chlorine is 2.0, so lithium
chloride (LiCl) is an ionic compound. The
difference in electronegativities between hydrogen
and chlorine is 0.9, so hydrogen chloride (HCl) is a
polar covalent molecule. The difference in
electronegativities between chlorine and chlorine is
zero, so dichloride (Cl2) is a nonpolar covalent
molecule.
The difference in electronegativities (∆EN) between
bonding atoms indicates the degree of ionic or
covalent character in the bond. If the difference in
electronegativities is larger than about 1.7, the bond
is said to be ionic. If the difference in
electronegativities is near zero, the bond is said to
be nonpolar covalent. If the difference in
electronegativities is greater than about 0.5 but less
than 1.7, the bond is said to be polar covalent.
For example, the difference in electronegativities
between lithium and chlorine is 2.0, so lithium
chloride (LiCl) is an ionic compound. The
difference in electronegativities between hydrogen
and chlorine is 0.9, so hydrogen chloride (HCl) is a
polar covalent molecule. The difference in
electronegativities between chlorine and chlorine is
zero, so dichloride (Cl2) is a nonpolar covalent
molecule.
Which of the following statements is not true?
Each C–O bond in the carbonate anion has a bond energy that is less than the bond energy value for a C–O double bond and greater than the bond energy value for a C–O triple bond. (D)
This is incorrect. A triple bond has more energy than a double bond because it has one more bond. In this situation, the actual bond order is somewhere between 1 and 2, not 2 and 3. So the observed bond energy for any bond would be somewhere between the bond energies for a single bond and a double bond of carbon and oxygen.
Carbon tetrachloride, CCl4, contains four C–Cl bonds. The reaction belowshows that a certain amount of energy is needed to break one of the C–Cl bonds. The products are CCl3 + Cl.
Successive addition of the same amount of energy will break one C–Cl bond at a time
CCl3 + energy → CCl2 + Cl
CCl2 + energy → CCl + Cl
CCl + energy → C + Cl
For each step, the energy needed to break one C–Cl bond is almost the same. This energy is called the bond energy.
Which of the following statements is not true about bond energy?
The average bond energy of a carbon-chlorine molecule is the energy you have to remove in order to break 1 mol of C–Cl bond. (C)
This would be true if you replaced the word remove with input or introduce.
Which of the following is the best definition of bond order?
Bond order is the number of electron-pair bonds between two atoms. (C)
This is the correct answer. Bond order is a numerical description of the number of bonds between two bonded atoms. For our studies, it varies between numerical values of 1 and 3.
Which of the following correctly ranks, in order from least to greatest, the distance between bonded atoms of the same element?
triple bond, double bond, single bond (A)
This is the correct answer. Theory predicts that as the bond strength increases (by adding more bonds), the distance between the atoms decreases. Since this question asked about the weakness, not the strength, this is the correct choice.
Which of the following table show the correct numerical order of the bond energy and the bond length of the thre kinds of C–O bonds.
(D)
Remember that as you add more bonds, you increase the bonding energy and thus decrease the bonding distance. For a molecule comprised of two atoms, each (additional) bond contributes (roughly) the same amount of bonding energy. So, when you have a single bond, it has a given energy. If you “add” another bond to the two bonded atoms, you basically double the bonding energy.
Bond order is a term that describes the number of electron-paired bonds that are located between atoms in a molecule. Which of the following statements about bond order is not true?
A molecule made of two different atoms will always have a bond order of 1. (D)
This is not true. There may be 1 − 3 bonds between the two atoms, which changes the bond order from 1 − 3, depending upon the details of the electron arrangement(s).
The bond energy of hydrogen molecule is 435 kJ per mole of hydrogen.
H–H + 435 kJ → H • + • H
Which of the following statements is not true?
If the two hydrogen atoms had a triple bond, the theoretical bond energy would be about 1,740 kJ. (C)
Theory predicts that you would need about 3*435 kJ = 1,305 kJ to break a triple bond. 1,740 kJ = 4 * 435 kJ.
The two resonance structures for the ozone molecule are:
Based on these structures, which statement below correctly describes particular bonds in the two structures?
In structure A, there is a double bond between the left and center oxygen atoms. In structure B, there is also a double bond between the right and center oxygen atoms. (D)
This is the correct answer. To give you even more information, in structure A, there is a single bond between the right and center oxygen atoms. In structure B, there is a single bond between the left and center oxygen atoms.
