Question

Identify the hybrid orbitals used by the central atom(s) and the type(s) of bonds formed in (a) FNO; (b) \(\mathrm{C}_{2} \mathrm{~F}_{4} ;\) (c) \((\mathrm{CN})_{2}\).

Short answer

(a) N in FNO uses sp^2 hybrid orbitals and forms sigma and pi bonds. (b) C in \(\text{C}_{2}\text{F}_{4}\) uses sp^2 orbitals, forms sigma and pi bonds. (c) C in (CN)_2 uses sp orbitals, forms sigma and pi bonds.

Step-by-step solution

- Determine the Lewis Structure for Each Molecule

Write the Lewis structure for each molecule to identify the central atoms and the bonding/arrangement of atoms. This will help in identifying the hybrid orbitals later. For example, in FNO, F is bonded to N, which is bonded to O.

- Identify the Central Atom

Identify the central atom for each molecule. For FNO, the central atom is N; for \(\text{C}_{2}\text{F}_{4}\), the central atoms are the two C atoms; and for (CN)_2, it is the C atoms.

- Determine the Total Number of Electron Regions Around the Central Atom

Count the number of electron regions (bonds + lone pairs) around each central atom. For FNO, N has 3 regions (2 bonds, 1 lone pair); for \(\text{C}_{2}\text{F}_{4}\), each C has 3 regions (2 bonds to F, 1 double bond to another C); and for (CN)_2, each C has 2 regions (triple bond and single bond).

- Determine the Hybridization of the Central Atom

Determine the hybridization based on the number of electron regions: 2 regions = sp; 3 regions = sp^2; 4 regions = sp^3. For FNO, N is sp^2 hybridized; for \(\text{C}_{2}\text{F}_{4}\), each C is sp^2 hybridized; and for (CN)_2, each C is sp hybridized.

- Identify the Types of Bonds

Identify the types of bonds (sigma or pi) formed in each molecule. In FNO, N forms two sigma bonds and one pi bond; in \(\text{C}_{2}\text{F}_{4}\), each C forms three sigma bonds and one pi bond; in (CN)_2, each C forms one sigma bond and two pi bonds.

Key concepts

Lewis Structure

The first step in understanding hybrid orbitals is to draw the Lewis structure of a molecule. Lewis structures represent the arrangement of atoms and the bonds between them, using dots for lone electrons and lines for bonds. For example, let's look at the molecule FNO. You start by determining the total number of valence electrons: F (7), N (5), and O (6), which sum up to 18. Then, arrange these electrons to show single bonds between F and N and N and O, with lone pairs added to complete the octet rule. This sets the stage for understanding electron regions and hybridization.

Central Atom Identification

In any given molecule, the central atom is typically the one with the lowest electronegativity (excluding hydrogen). In the molecule FNO, the nitrogen (N) atom is the central atom because it is bonded to both fluorine (F) and oxygen (O). Likewise, in \(\text{C}_{2}\text{F}_{4}\), the central atoms are the two carbon (C) atoms, and in (CN)_2, each cyanide group has a carbon (C) atom as the central atom. Identifying the central atom helps us understand how other atoms are bonded around it and lays the groundwork for determining electron regions.

Electron Regions

Electron regions around a central atom include both bonding pairs (shared electrons) and lone pairs (non-bonding electrons). In the molecule FNO, nitrogen is surrounded by three electron regions: two bonding pairs (one with F and one with O) and one lone pair. For the molecule (\(\text{C}_{2}\text{F}_{4}\)), each carbon atom has three electron regions: two bonding pairs with fluorine atoms and one bonding pair forming a double bond with another carbon atom. In (CN)_2, each carbon atom has two electron regions: one triple bond with nitrogen and one single bond with the other carbon atom. Counting these regions helps in determining the type of hybridization.

Hybridization Types

Hybridization involves mixing atomic orbitals to form new hybrid orbitals. The type of hybridization depends on the number of electron regions around the central atom:
\(2\) regions = \(sp\) hybridization,
\(3\) regions = \(sp^2\) hybridization, and
\(4\) regions = \(sp^3\) hybridization.
In FNO, nitrogen is \(sp^2\) hybridized because it has three electron regions. In \(\text{C}_{2}\text{F}_{4}\), each carbon is \(sp^2\) hybridized due to three electron regions. For (CN)_2, each carbon atom is \(sp\) hybridized because there are two electron regions. Understanding these hybridizations is crucial for predicting molecule shape and bond angles.

Sigma and Pi Bonds

Bonds between atoms are classified into sigma (σ) and pi (π) bonds. Sigma bonds result from the head-on overlap of atomic orbitals and are the first bond formed between two atoms. In contrast, pi bonds result from the side-to-side overlap of p-orbitals and are found in double and triple bonds, alongside sigma bonds.
For example, in FNO, nitrogen forms two sigma bonds (with F and O) and one pi bond (with O). In the molecule \(\text{C}_{2}\text{F}_{4}\), each carbon forms three sigma bonds and one pi bond (in the C=C double bond). In (CN)_2, each carbon forms one sigma bond and two pi bonds (in the C≡N triple bond). These distinctions help explain the molecule's rigidity and reactivity.