Question

Which of the following molecules do not exist? (1) \(\mathrm{II}_{2}\) (2) \(\mathrm{Bc}_{2}\) (3) \(\mathrm{C}_{2}\) (4) \(\mathrm{N}_{2}\)

Short answer

\text{Bc}_{2} does not exist.

Step-by-step solution

Analyze Molecular Possible Structures

Analyze each molecular formula to determine which is not a stable molecule. Known diatomic molecules are usually combinations of the same element or specific pairs.

Assess Given Molecules

Evaluate each molecule to see if it follows the usual chemical bonding rules: 1. \(\text{II}_{2}\): Iodine typically forms \(I_2 \)2. \(\text{Bc}_{2}\): Not a common or known stable molecule.3. \(\text{C}_{2}\): Carbon can form C_2 but it is not stable as a diatomic molecule.4. \(\text{N}_{2}\): Nitrogen forms a stable diatomic molecule (N_2).

Evaluation of Stability

Evaluate each molecule's stability based on known chemical rules. 1. \(I_2 \) is a stable diatomic molecule. 2. Bc_2 does not exist as a recognized stable molecule. 3. \(C_2 \) is a theoretical molecule but generally unstable in diatomic form. 4. \(N_2 \) is a stable diatomic molecule.

Conclusion

Conclude that out of the given molecules, \(\text{Bc}_{2}\) does not exist based on chemical stability and bonding principles.

Key concepts

Molecular Stability

Understanding molecular stability is crucial in determining whether a molecule can exist in nature. A molecule is stable if the total energy of the system is minimized when all atoms are bonded. When atoms combine, they share or transfer electrons to achieve full outer electron shells, usually resembling the nearest noble gas configuration. Stability is influenced by factors like bond energy, electron configuration, and intermolecular forces.
When looking at a molecule, one must consider:

• The number of valence electrons each atom shares or exchanges.
• The presence of any unpaired electrons left after bonding.
• The overall electronic structure achieving a lower energy state.

For example, the molecule \(\text{Bc}_{2}\) analyzed in the exercise doesn't exist because it cannot achieve a stable electronic configuration. On the other hand, \(\text{N}_{2}\) is highly stable due to its triple bond, resulting in a full outer shell for both nitrogen atoms and a lower energy state.

Diatomic Molecules

Diatomic molecules are composed of only two atoms, which can be of the same or different elements. The seven elements that naturally occur as diatomic molecules in their free form at standard conditions are hydrogen (H₂), nitrogen (N₂), oxygen (O₂), fluorine (F₂), chlorine (Cl₂), bromine (Br₂), and iodine (I₂). These elements form molecules with two atoms because this bonding achieves a lower energy state and thus greater stability.
When considering diatomic molecules, remember:

• They often form bonds to complete their valence electron shell.
• Elements like nitrogen form triple bonds, while oxygen forms double bonds, and halogens typically form single bonds.
• Molecular bond types (single, double, triple) influence the molecule's strength and stability.

In the exercise, diatomic molecules analyzed were \(\text{I}_{2}\), \(\text{C}_{2}\), and \(\text{N}_{2}\). While \(\text{I}_{2}\) and \(\text{N}_{2}\) are stable, \(\text{C}_{2}\) does not typically exist in a stable diatomic form at standard conditions.

Chemical Bonding Rules

Chemical bonding rules are the guidelines that explain how atoms combine to form molecules. These rules include concepts like the octet rule, bond types, bond energy, and molecular geometry. The octet rule states that atoms tend to form bonds to achieve eight electrons in their valence shell, mimicking the electron configuration of noble gases. However, there are exceptions to this rule.
Essential bonding concepts:

• Covalent bonds involve sharing electrons between atoms.
• Ionic bonds involve the transfer of electrons from one atom to another.
• Metallic bonds involve a 'sea of electrons' shared among a lattice of metal atoms.

In covalent bonds, atoms share electrons to complete their valence shells. Single, double, and triple bonds count differently towards an atom's octet. The molecule \(\text{N}_{2}\) features a robust triple covalent bond, making it exceptionally stable. Conversely, \(\text{Bc}_{2}\) does not form because boron and carbon do not pair to create a stable bond under typical conditions.