In the Lewis structure shown below, A, D, E, Q, X, and Z...

In the Lewis structure shown below, $A, D, E, Q, X$, and $Z$ represent elements in the first two rows of the periodic table (H-Ne). Identify all six elements so that the formal charges of all atoms are zero. [Section 8.3]

Key Concepts

Periodic Table Trends (First Two Rows)

Elements in the first two rows of the periodic table (such as hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon) have characteristic properties including specific valence electron counts and atomic sizes. Understanding these trends is important when assigning atoms in a Lewis structure because these characteristics affect bond formation, electronegativity, and the ability to satisfy both the octet (or duet) rule and achieve zero formal charges.

Octet Rule

The octet rule is a chemical rule of thumb that suggests atoms tend to form bonds in such a way that each atom has eight electrons in its valence shell, similar to the electron configuration of a noble gas. This rule is significant when drawing Lewis structures as it helps predict the most stable electron arrangement, particularly for atoms in the second period, though there are exceptions such as hydrogen which follows the duet rule.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom that are available for bonding. The number of valence electrons determines how atoms interact with each other, as seen in the Lewis structure. For atoms in the first two rows of the periodic table, the valence electron count plays a significant role in determining both the type of bonds that can be formed and the adherence to rules like the octet rule.

Formal Charges

Formal charge is a concept used to assign a charge to each atom in a molecule, based on the assumption that electrons in chemical bonds are shared equally between atoms. It is calculated by comparing the number of valence electrons of a free atom with the number of electrons assigned to it in the molecule. A structure in which all formal charges are zero is often the most stable and is a key criterion when evaluating alternative Lewis structures.

Lewis Structures

A Lewis structure is a diagrammatic representation that shows the bonding between atoms of a molecule and the lone pairs of electrons that may exist. It is used to visualize how the electrons are distributed among the atoms, allowing for the prediction of structural features such as bonds and lone pairs, which are crucial for understanding molecular geometry and reactivity.

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