The mixing of atomic orbitals on one atom to produce a new set of equivalent orbitals for bonding is called hybridization.
Missing Word
hybridization
Hybridization combines an atom's s, p and sometimes d orbitals into equivalent orbitals pointed in the directions that match the observed molecular geometry.
Category: Hybrid Orbitals
Question 2
In valence bond theory, a covalent bond forms through the overlap of half-filled atomic orbitals on two atoms.
Missing Word
overlap
Overlap is the sharing of the same region of space by orbitals on two atoms. The greater the overlap, the more electron density lies between the nuclei and the stronger the bond.
Category: Valence Bond Theory
Question 3
A covalent bond whose electron density lies along the line joining the two nuclei, as in every single bond, is a sigma bond.
Missing Word
sigma
A sigma bond arises from end-to-end orbital overlap. The first bond formed between any two atoms is a sigma bond.
Category: Valence Bond Theory
Question 4
A bond formed from two parallel p orbitals merging side by side, with electron density above and below the bond axis, is a pi bond.
Missing Word
pi
A pi bond results from side-by-side overlap of unhybridized p orbitals. It is the second bond in a double bond and the second and third bonds in a triple bond.
Category: Multiple Bonds
Question 5
Unlike the dumbbell-shaped p orbitals, s orbitals have a spherical shape, so two s orbitals combine the same way from any direction of approach.
Missing Word
spherical
An s orbital has the same electron density in every direction from the nucleus. Its overlap therefore does not depend on orientation, unlike the directional p orbitals.
Category: Valence Bond Theory
Question 6
The energy of two hydrogen atoms reaches its minimum at a separation of 74 picometers, the H-H bond length.
Missing Word
74
The H2 bond length is 74 pm, the distance at which attraction and repulsion balance and the energy is lowest. Pushing the atoms closer raises the energy sharply.
Category: Valence Bond Theory
Question 7
Mixing one s orbital with three p orbitals on the same atom produces 4 equivalent sp3 orbitals that point to the corners of a tetrahedron.
Missing Word
4
The number of hybrid orbitals equals the number of atomic orbitals mixed, so one s and three p orbitals give four sp3 orbitals. This set fits four regions of electron density, as in CH4.
Category: Hybrid Orbitals
Question 8
Because its pi bond requires parallel p orbitals, all six atoms of ethene lie in one flat arrangement, so the molecule is planar.
Missing Word
planar
Planar means all atoms lie in a single plane. Twisting ethene out of this arrangement would reduce the side-by-side contact of the p orbitals and break the pi bond.
Category: Multiple Bonds
Question 9
C6H6, a ring of six sp2 hybridized carbon atoms whose pi electrons are spread over the whole ring, is called benzene.
Missing Word
benzene
Benzene is a planar ring of carbon atoms in which the pi electrons are delocalized rather than fixed in alternating double bonds. Molecular orbital theory describes this delocalization better than valence bond theory.
Category: Multiple Bonds
Question 10
A molecular orbital with zero electron density midway between the nuclei, whose electrons weaken the bond, is described as antibonding.
Missing Word
antibonding
An antibonding orbital forms from the out-of-phase combination of atomic orbitals. It lies higher in energy than the original orbitals, and its electrons reduce the bond order.
Category: Molecular Orbitals
Question 11
A region of an orbital where the probability of finding an electron is zero is called a node.
Missing Word
node
A node is a point or surface where an orbital's electron density is zero. Antibonding orbitals have a node between the nuclei, and pi orbitals have a nodal plane along the bond axis.
Category: Molecular Orbitals
Question 12
Orbitals that have exactly the same energy, such as the two pi 2p bonding orbitals of a diatomic molecule, are called degenerate.
Missing Word
degenerate
Degenerate orbitals share an identical energy. Electrons fill a degenerate set singly before pairing, which is why some molecules end up with unpaired electrons.
Category: Molecular Orbitals
Question 13
Molecular orbital theory gives the N2 molecule a bond order of 3, matching its Lewis triple bond.
Missing Word
3
N2 has 8 valence electrons in bonding orbitals and 2 in antibonding orbitals, so its bond order is (8 - 2) / 2 = 3. This high bond order makes N2 very stable.
Category: Bond Order and Magnetism
Question 14
A substance with unpaired electrons that is drawn into a magnetic field is described as paramagnetic.
Missing Word
paramagnetic
Paramagnetic substances contain unpaired electrons, whose spins align with an applied magnetic field. O2 and B2 are paramagnetic examples.
Category: Bond Order and Magnetism
Question 15
A molecule in which every electron is paired is weakly repelled by a magnetic field and is called diamagnetic.
Missing Word
diamagnetic
Diamagnetic substances have no unpaired electrons and are pushed slightly out of a magnetic field. N2 and F2 are diamagnetic molecules.
Category: Bond Order and Magnetism