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[Chemical Knowledge]：How to write Lewis structural formula

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Lewis structural formula is the chemical bond between the atoms in the molecule, and it is also the common unpaired electron pair in the molecule. Therefore, it can be used to indicate the position of chemical bonds in molecules and the distribution of electrons between atoms. In this article, we will discuss the writing of Lewis structural formula and the matters needing attention.

Four Basic Steps in Writing Lewis Structural Formula

Writing Lewis Structural Formula of a molecule requires the following four steps:

Step 1: Determine the Total Electron Number of the molecule

First, you need to know the total electron number of the molecule. This step not only determines the number of electrons in the molecule, but also determines the number of electrons that will pair up (except hydrogen atoms). In general, the method of calculating the total electron number is:
the total electron number of
= the number of individual electrons in the chemical bond (for example, one electron in a hydrogen atom) the number of electrons in the outer layer of each atom.

Step 2: Determine the central atom

To write the Lewis structural formula of the molecule, you must know which atom is the central atom. To determine this, you need to consider the actual situation in the experiment (usually, the central atom is the most electronegativity atom). In almost all cases, the central atom is a large number of electronegativity atoms (especially oxygen, nitrogen, and sulfur) that can form chemical bonds with multiple atoms, and sometimes also metal atoms, such as hydrogen in coal gas.

Step 3: Connecting Atomic

should now know the total number of electrons in the molecule and the atomic sign of the central atom. Next, the central atom needs to be connected to other atoms by chemical bonds. If enough electrons are made to share, chemical bonds can be formed. In this step, molecular bonds and non-bonding electron pairs should be drawn.

Step 4: Check the result

After drawing all atoms and chemical bonds, you need to check whether the result is correct. It must be ensured that each atom is completely contained in the Lewis formula and that all atoms follow the eight-electron rule. In most cases, the Lewis structural formula will uniquely determine the geometric structure of the molecule, but the VSEPR (electron repulsion theory of molecular morphology) of the molecule must be further analyzed in order to further determine the geometric structure of the molecule. Matters needing attention in

should pay attention to the following aspects when using Lewis structural formula:

1. Eight-electron principle

In order to follow the eight-electron rule, atoms with less than eight outer electron layers need to obtain additional electrons by forming chemical bonds with other atoms. However, elements such as B, Be, and Al do not require eight electrons to be stable, so they may not conform to the eight-electron rule in a Lewis structure.

2. Foot Principle

chemical bond structure is the bonding principle, which helps to stabilize atoms beyond the eight-electron rule through sp3 hybrid atoms. In Lewis structure, lone pair electrons are used to cross the line between atoms to form asymmetric pushing. This can avoid the formation of unstable resonances during long bond lengths.

3. Different electronegativity

When the electronegativity between atoms is different, it is necessary to draw the polar structure. In this case, the shared electron pair will be closer to the electronegative atom. For common electron pairs, the electron pairs of the inferior electronegative element should be placed around the inferior electronegative atom.