Lewis structure generator

Lewis structure calculator


Common Molecules:

The Lewis Structure Generator that we put in your hands here is an excellent tool to obtain structures of more than 400 molecules.

To use the Lewis Structure Calculator follow these steps:

  1. Enter the formula of the molecule in the field provided for it. For example, if we want to obtain the Lewis structure of the Sulfate ion, SO4– 2, we must first enter the charge by typing (-2) or by entering -2 in the charge field and pressing the «Add» button. Then we write the rest of the formula being as follows: (-2)SO4. A list of common molecules is also provided.
  2. Once the formula has been entered, you just have to press the “Generate” button and a window with the desired Lewis structure will automatically be displayed. To save the image of the structure on your computer, you just have to click on “Download”.

In addition to the Lewis structure calculator, here is a summary of the main theoretical concepts related to Lewis dot diagrams and some examples.

Lewis structure definition | What is a Lewis dot diagram?

The formation of a chemical bond (ionic and covalent) involves the transfer of electrons or the exchange of electrons. Lewis structures can be used to represent valence shell electrons in a chemical bond.

The Lewis structure, proposed by Gilbert Newton Lewis, who introduced it for the first time in 1916, is a graphic representation of the sharing of electrons that occurs in chemical bonds between atoms of the same or different species. These bonds can be single, double, or triple.

These type diagrams are a simplified representation of the valence shell electrons in a molecule. Lewis structures can be made for molecules that contain covalent bonds and for coordination compounds. The reason is that electrons are shared in a covalent bond. In an ionic bond, it is more like one atom donating an electron to the other atom.

How to draw Lewis structures

Given a chemical formula corresponding to a molecule or molecular ion, the steps to obtain its Lewis structure are as follows:

  1. First, it is important to get a correct count of all the valence electrons. One way to do such a count is to write Lewis symbols for all the atoms in the formula and count all the “dots.” For an (uncharged) molecule, that count is the correct number of valence electrons. For polyatomic ions, add the valence electrons of all atoms in the formula and subtract one electron for each positive charge on a cation and add one electron for each unit negative charge on an anion.
  2. The second step is to draw a skeletal structure. Which will help us decide how the atoms will bond. Choose a central atom (we will take as examples small molecules for which there is only one central atom, and the other atoms, the peripheral atoms, are all attached to the central atom). Hydrogen (H) and fluorine (F) each have a valence of 1, and generally these will not be central atoms (bonded to more than one atom). Given a formula, the central atom is typically the first atom (eg ClF 4 ), although this convention is not always followed (eg HNO 3 ). Another good way to choose is to choose the least electronegative atom. Inevitably, there will be cases where it is possible to draw more than one skeletal structure.
    Draw bonds as lines between atoms. Each bond counts as 2 e .
  3. Add electrons as lone nonbonding pairs around peripheral atoms so they have octets (eight electrons total). Note that this does not apply to hydrogen H, which can only accommodate a duo (2 e ).
  4. Add the remaining pairs of electrons to the central atom so your octet is complete (if it isn’t already). Never exceed an octet for an atom of period 2! For periods 3 and larger, the atoms are large enough to accommodate more than one octet in their valence bond shell. If no more electrons are available and the central one does not yet have a full octet, a lone pair on a peripheral atom can be pushed into a second (or third) bond with the central atom. Carbon and nitrogen are second-period elements that commonly form double and triple bonds as central atoms, and oxygen as the peripheral atom is often in a double bond with the central atom.
  5. If all atoms in the second period and above have at least one octet, and no atom in the second period exceeds an octet, and the total number of electrons in bonds and lone pairs equals the total number of available valence electrons, then we have produced a valid Lewis structure. The convention for ions is to enclose the structure in parentheses and indicate the net charge in the upper right corner.

Note that there are some cases where the best Lewis structure has an incomplete octet on a central atom. Since it is often possible to draw more than one valid Lewis structure for a molecule or molecular ion, we will need to assess which ones are more plausible or make better chemical sense. As noted above, formal charge is used as a guide in that zero or a minimum total number of formal charges is generally best, and the formal charge of an atom is considered relative to its electronegativity. Remember, a Lewis structure is not the molecule, but just a graphical representation intended to convey certain information about it. Such a representation informs the prediction of the likely physical or chemical properties of the actual molecule or of the bulk substance that is composed of those molecules. One of the most common uses we make of a valid Lewis structure (and for this we don’t need the best Lewis structure, just any valid one) is to predict molecular shape and polarity.

Lewis structure examples

PCl3 lewis structure

PCl3 lewis structure

CH2Cl2 lewis structure

CH2Cl2 lewis structure

XeF2 lewis structure

XeF2 lewis structure

All structures in the examples have been generated with the Lewis structure calculator.

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