Valence Bond Theory

How does valence bond theory explain chemical bonding?

Valence bond theory states that covalent bonds form when valence orbitals from two atoms overlap and their unpaired electrons pair with opposite spins, creating shared electron density between the atoms

What is hybridization, and how does it affect the bonding and shape of molecules?

Hybridization is the process of mixing atomic orbitals to form new hybrid orbitals with different shapes and energies, which determines molecular geometry and bond angles

How can you determine the hybridization of an atom in a molecule?

Draw the Lewis structure, count the number of bonded atoms and lone pairs around the central atom, add them to get the number of hybrid orbitals, then match to the corresponding hybridization type (sp, sp², sp³, etc.)

What are sigma bonds and pi bonds? How do they differ?

Sigma (σ) bonds form from head-on orbital overlap along the bond axis, while pi (π) bonds form from side-by-side overlap of unhybridized p orbitals, σ bonds are stronger and always form first

According to valence bond theory, what happens to electron spins when two atoms approach each other to form a bond?

One electron flips spin so the two unpaired electrons can pair up and form a stable bond

Why does orbital overlap lower potential energy during bond formation?

Overlap increases electron density between nuclei, strengthening attraction between nuclei and shared electrons, thus lowering potential energy

What is the term for the lowest potential energy point in a bond energy diagram?

Bond enthalpy or bond energy — the energy released when a bond forms

What determines the stability of a bond according to valence bond theory?

The balance between attractive and repulsive forces at the bond length, where potential energy is minimized

Define hybrid orbitals and explain when they form.

Hybrid orbitals are new orbitals formed by mixing atomic orbitals during bonding to create orbitals of intermediate energy and shape

What types of orbitals mix to form sp hybrid orbitals, and what is their geometry?

One s and one p orbital mix to form two sp orbitals arranged linearly with a bond angle of 180°

What is the s and p character percentage in an sp hybrid orbital?

50% s character and 50% p character

What orbitals combine to form sp² hybrid orbitals, and what is their shape?

One s and two p orbitals mix to form three sp² hybrid orbitals arranged in a trigonal planar geometry (120° bond angles)

How does the energy of an sp² orbital compare to that of an sp orbital?

sp² orbitals have higher energy because they contain more p character, making them closer in energy to pure p orbitals

If an atom has three regions of electron density (bonding or lone pairs), what is its hybridization?

sp²

If an atom has four regions of electron density, what is its hybridization?

sp³

How does the shortcut for determining hybridization simplify the process?

By counting the number of atoms bonded to the central atom and the number of lone pairs, you can directly determine the number and type of hybrid orbitals needed

In the molecule BeCl₂, what hybridization occurs in the central atom, and what geometry results?

The Be atom undergoes sp hybridization, producing a linear geometry (180°)

Explain why sp hybridization results in linear geometry.

Two sp orbitals repel each other to maximize separation, arranging themselves 180° apart

What is the relationship between s character and bond strength?

Higher s character increases bond strength because s orbitals are closer to the nucleus, leading to stronger overlap

Why are bond-line structures used in organic chemistry?

They simplify drawing by omitting carbon and hydrogen symbols, showing only bond angles and connections

In bond-line structures, what is the hybridization of each carbon atom by default?

sp³

How does hybridization influence molecular shape according to valence bond theory?

The type of hybrid orbitals formed determines the angles and arrangement of bonds, shaping the overall geometry of the molecule

Why do hybrid orbitals form only during bonding?

They arise from the need to minimize energy and optimize overlap when atoms combine

What is the difference in energy and shape between hybrid and pure atomic orbitals?

Hybrid orbitals have intermediate energies and distinct shapes that align better for bonding compared to pure s or p orbitals