Uploaded March 2024 | Updated September 2026, 2 weeks ago
Writing Lewis structures is an important skill in chemistry for visualizing the arrangement of electrons in molecules and ions. Here's a structured guide on how to draw them:
Count the Valence Electrons: Begin by determining the total number of valence electrons available for bonding. This is done by adding up the valence electrons of each atom in the molecule or ion. For ions, adjust the total by adding electrons for negative charges or subtracting electrons for positive charges.
Choose the Central Atom: Place the least electronegative element in the center of your structure, as it is more likely to share electrons. Hydrogen and halogens are exceptions; they are almost always placed on the outside since hydrogen can only form one bond, and halogens typically form one bond as well.
Sketch a Skeleton Structure: Connect the central atom to the outer atoms with single bonds. Each line represents a pair of shared electrons.
Complete the Octets of the Outer Atoms: Distribute the remaining valence electrons around the outer atoms to complete their octets (8 electrons around each atom), except for hydrogen, which is stable with 2 electrons. Start by placing electron pairs around the atoms until each gets an octet or, in the case of hydrogen, a duet.
Place Remaining Electrons on the Central Atom: After the outer atoms have their octets, place any remaining electrons on the central atom.
Form Double or Triple Bonds if Necessary: If the central atom does not have an octet after distributing the electrons, consider forming double or triple bonds by sharing electrons from the outer atoms. This often occurs when there are not enough electrons to complete octets with single bonds alone.
Review for Exceptions to the Octet Rule: Keep in mind that there are exceptions to the octet rule. Some elements can have less (e.g., boron) or more (e.g., sulfur, phosphorus) than eight electrons. These exceptions are based on the specific requirements of the molecule's structure and the elements involved.
Finalize the Structure: Review the structure to ensure that all valence electrons are accounted for and that all atoms (except for exceptions) follow the octet rule. Adjust as necessary, considering resonance structures if applicable, where multiple valid structures can represent a molecule.
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Writing Lewis structures is an important skill in chemistry for visualizing the arrangement of electrons in molecules and ions. Here's a structured guide on how to draw them:
Count the Valence Electrons: Begin by determining the total number of valence electrons available for bonding. This is done by adding up the valence electrons of each atom in the molecule or ion. For ions, adjust the total by adding electrons for negative charges or subtracting electrons for positive charges.
Choose the Central Atom: Place the least electronegative element in the center of your structure, as it is more likely to share electrons. Hydrogen and halogens are exceptions; they are almost always placed on the outside since hydrogen can only form one bond, and halogens typically form one bond as well.
Sketch a Skeleton Structure: Connect the central atom to the outer atoms with single bonds. Each line represents a pair of shared electrons.
Complete the Octets of the Outer Atoms: Distribute the remaining valence electrons around the outer atoms to complete their octets (8 electrons around each atom), except for hydrogen, which is stable with 2 electrons. Start by placing electron pairs around the atoms until each gets an octet or, in the case of hydrogen, a duet.
Place Remaining Electrons on the Central Atom: After the outer atoms have their octets, place any remaining electrons on the central atom.
Form Double or Triple Bonds if Necessary: If the central atom does not have an octet after distributing the electrons, consider forming double or triple bonds by sharing electrons from the outer atoms. This often occurs when there are not enough electrons to complete octets with single bonds alone.
Review for Exceptions to the Octet Rule: Keep in mind that there are exceptions to the octet rule. Some elements can have less (e.g., boron) or more (e.g., sulfur, phosphorus) than eight electrons. These exceptions are based on the specific requirements of the molecule's structure and the elements involved.
Finalize the Structure: Review the structure to ensure that all valence electrons are accounted for and that all atoms (except for exceptions) follow the octet rule. Adjust as necessary, considering resonance structures if applicable, where multiple valid structures can represent a molecule.
Join this channel to get full access to Dr. B's chemistry guides:
youtube.com/channel/UCaUF73YX-uQTGwDB20I3n3g/join
