When drawing Lewis structure to be valid, each atom must have a full octet of 8 electrons (except hydrogen, which only has a duet of 2 electrons). The structure with both of the hydrogens and both of the fluorines bonded to the carbon allows all atoms to have the proper number of electrons (if the lone pairs on the fluorine atoms are included). In the structure below, fluorine has six electrons in three lone pairs (not drawn) and the seventh electron participating in a covalent single bond to the Carbon, which allows the Fluorine to have an octet. Likewise, the carbon achieves its octet by sharing bonds with the two F and two H allows. Hope this helps.

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The ChemDoodle Web Components library is a pure JavaScript chemical graphics and cheminformatics library derived from the ChemDoodle application and produced by iChemLabs. ChemDoodle Web Components allow the wielder to present publication quality 2D and 3D graphics and animations for chemical structures, reactions and spectra. Apr 27, 2017 Most resonance structures and coordination compounds are also supported. Simply follow the steps below: If you do not already know the name or chemical formula of the molecule you wish to generate a dot structure for, you can browse the list of molecules at molcalc.org by clicking here.

H-C-H

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Lewis structures, also known as Lewis dot formulas,Lewis dot structures, electron dot structures, or Lewis electron dot structures (LEDS), are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.^[1]^[2]^[3] A Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. The Lewis structure was named after Gilbert N. Lewis, who introduced it in his 1916 article The Atom and the Molecule.^[4] Lewis structures extend the concept of the electron dot diagram by adding lines between atoms to represent shared pairs in a chemical bond.

Lewis structures show each atom and its position in the structure of the molecule using its chemical symbol. Lines are drawn between atoms that are bonded to one another (pairs of dots can be used instead of lines). Excess electrons that form lone pairs are represented as pairs of dots, and are placed next to the atoms.

Although main group elements of the second period and beyond usually react by gaining, losing, or sharing electrons until they have achieved a valence shell electron configuration with a full octet of (8) electrons, hydrogen (H) can only form bonds which share just two electrons.

Construction and electron counting[edit]

The total number of electrons represented in a Lewis structure is equal to the sum of the numbers of valence electrons on each individual atom. Non-valence electrons are not represented in Lewis structures.

Once the total number of available electrons has been determined, electrons must be placed into the structure according to these steps:

The atoms are first connected by single bonds.
If t is the total number of electrons and n the number of single bonds, t-2n electrons remain to be placed. These should be placed as lone pairs: one pair of dots for each pair of electrons available. Lone pairs should initially be placed on outer atoms (other than hydrogen) until each outer atom has eight electrons in bonding pairs and lone pairs; extra lone pairs may then be placed on the central atom. When in doubt, lone pairs should be placed on more electronegative atoms first.
Once all lone pairs are placed, atoms (especially the central atoms) may not have an octet of electrons. In this case, the atoms must form a double bond; a lone pair of electrons is moved to form a second bond between the two atoms. As the bonding pair is shared between the two atoms, the atom that originally had the lone pair still has an octet; the other atom now has two more electrons in its valence shell.

Lewis structures for polyatomic ions may be drawn by the same method. When counting electrons, negative ions should have extra electrons placed in their Lewis structures; positive ions should have fewer electrons than an uncharged molecule. When the Lewis structure of an ion is written, the entire structure is placed in brackets, and the charge is written as a superscript on the upper right, outside the brackets.

A simpler method has been proposed for constructing Lewis structures, eliminating the need for electron counting: the atoms are drawn showing the valence electrons; bonds are then formed by pairing up valence electrons of the atoms involved in the bond-making process, and anions and cations are formed by adding or removing electrons to/from the appropriate atoms.^[5]

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A trick is to count up valence electrons, then count up the number of electrons needed to complete the octet rule (or with hydrogen just 2 electrons), then take the difference of these two numbers. The answer is the number of electrons that make up the bonds. The rest of the electrons just go to fill all the other atoms' octets.

Another simple and general procedure to write Lewis structures and resonance forms has been proposed.^[6]

Formal charge[edit]

In terms of Lewis structures, formal charge is used in the description, comparison, and assessment of likely topological and resonance structures^[7] by determining the apparent electronic charge of each atom within, based upon its electron dot structure, assuming exclusive covalency or non-polar bonding. It has uses in determining possible electron re-configuration when referring to reaction mechanisms, and often results in the same sign as the partial charge of the atom, with exceptions. In general, the formal charge of an atom can be calculated using the following formula, assuming non-standard definitions for the markup used:

{displaystyle C_{f}=N_{v}-U_{e}-{frac {B_{n}}{2}}}

where:

${displaystyle C_{f}}$ is the formal charge.
${displaystyle N_{v}}$ represents the number of valence electrons in a free atom of the element.
${displaystyle U_{e}}$ represents the number of unshared electrons on the atom.
${displaystyle B_{n}}$ represents the total number of electrons in bonds the atom has with another.

The formal charge of an atom is computed as the difference between the number of valence electrons that a neutral atom would have and the number of electrons that belong to it in

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