Question

A rule for drawing plausible Lewis structures is that the central atom is generally less electronegative than the surrounding atoms. Explain why this is so.

Short answer

Less electronegative atoms as central atoms allow more stable and symmetric electron distribution in Lewis structures.

Step-by-step solution

Understanding Electronegativity

Electronegativity is a chemical property that describes how strongly an atom can attract a pair of shared electrons towards itself. Generally, atoms with higher electronegativity are more effective at attracting electrons.

Central Atom Characteristics

In a Lewis structure, the central atom is usually the one with the lowest electronegativity because it is less effective at pulling electrons away from other atoms. Instead, it shares its electrons with them, forming stable covalent bonds.

Stability of Lewis Structures

A stable Lewis structure minimizes the potential energy of the molecule by efficiently distributing electrons. A less electronegative central atom helps in spreading electron density rather than drawing it all towards itself, promoting symmetry and stability in the molecule.

Key concepts

Electronegativity

Electronegativity is the ability of an atom to attract shared electrons towards itself in a chemical bond. This is a crucial concept in chemistry as it influences how atoms bond with each other. Atoms with high electronegativity attract electrons more strongly. This affects the type and nature of the bonds that form between atoms. Notably, electronegativity values can predict the behavior of atoms in molecules:

• If the electronegativity difference between two atoms is significant, the bond tends to be ionic.
• If the difference is small, a covalent bond forms.
• Electronegativity affects the polarity of molecules, influencing properties like solubility and melting points.

When drawing Lewis structures, understanding electronegativity helps determine the placement of atoms. Atoms with lower electronegativity often serve better as central atoms.

Central Atom

In the construction of Lewis structures, identifying the central atom is a fundamental step. The central atom is often the one with the lowest electronegativity, allowing other atoms to connect around it effectively. This concept ties back to the ability of atoms to form stable structures by sharing electrons. The central atom's role includes:

• Serving as the nucleus around which other atoms are arranged.
• Providing a framework for bond formation.
• Facilitating the distribution of electron pairs required for bonds.

The choice of a less electronegative atom ensures that the molecule can achieve a symmetric and stable electronic configuration. In practice, the central atom usually forms the most bonds within the molecule.

Covalent Bonds

Covalent bonds are chemical links between atoms achieved by sharing electron pairs. These bonds allow atoms to attain a more stable electronic configuration akin to the noble gases. Understanding how these bonds form is crucial to comprehending molecular structures. Key characteristics of covalent bonds include:

• They involve the sharing of electrons rather than complete transfer.
• Covalent bonds often form between atoms with similar electronegativities.
• These bonds result in the formation of molecules with specific three-dimensional shapes.

In Lewis structures, covalent bonds are represented by lines connecting atoms, each line indicating a pair of shared electrons. The strength and length of covalent bonds depend on the atoms involved and the number of shared electron pairs.

Molecular Stability

Molecular stability is a measure of how resistant a molecular structure is to change under normal conditions. Stable molecules have low potential energy and are less likely to react or decompose. Several factors contribute to molecular stability:

• The distribution of electrons in the molecule.
• The electronegativity of its constituent atoms.
• The symmetry of the molecule.

When creating Lewis structures, achieving molecular stability involves assigning electrons in a way that minimizes repulsion and maximizes symmetry. A central atom with low electronegativity can help achieve this by distributing electron density evenly, ensuring all atoms within the molecule reach a satisfied and low-energy state. This leads to the optimization of the molecule's shape and stability.