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Lewis structures
Lewis structures
Lewis structures are used to predict the bonding and shape of molecules by representing valence electrons, including the covalent bonds between atoms and any unbonded pairs.
Lewis structures are used to predict the bonding and shape of molecules by representing valence electrons, including the covalent bonds between atoms and any unbonded pairs.
Scan the QR code for further details on basic Lewis structures, as well as molecular geometry and polarity.
Scan the QR code for further details on basic Lewis structures, as well as molecular geometry and polarity.
Steps needed to draw Lewis Structures:
Steps needed to draw Lewis Structures:
Count the number of valence electrons for the molecule.
Count the number of valence electrons for the molecule.
Write the skeleton structure, with the least electronegative element being in the middle. If there is a single type of atom only in a molecule this will be the central atom. Remember C is a common central atom, whilst H and F are never central atoms.
Write the skeleton structure, with the least electronegative element being in the middle. If there is a single type of atom only in a molecule this will be the central atom. Remember C is a common central atom, whilst H and F are never central atoms.
Connect the atoms up, using either 2 dots to show 2 valence electrons being shared (1 from each atom), or a single line, which shows the same
Connect the atoms up, using either 2 dots to show 2 valence electrons being shared (1 from each atom), or a single line, which shows the same
Fill in the valence electrons for the outer atoms, remembering that these atoms need 8, for a full shell (OCTET RULE). Arrange them in pairs, as electrons pair up in sub orbitals (in opposite spins). Further information about electron shells and sub orbitals, relevant to L3 Chemistry can be accessed in a separate post.
Fill in the valence electrons for the outer atoms, remembering that these atoms need 8, for a full shell (OCTET RULE). Arrange them in pairs, as electrons pair up in sub orbitals (in opposite spins). Further information about electron shells and sub orbitals, relevant to L3 Chemistry can be accessed in a separate post.
Place the remaining electrons around the central atom, so this atom also has 8 valence electrons. To ensure the central atom, as well as the outer atoms, also abides by the octet rule you may have to rearrange the placement of electrons, which may lead to double bonds, triple bonds and lone pairs of electrons (unbonded electrons)
Place the remaining electrons around the central atom, so this atom also has 8 valence electrons. To ensure the central atom, as well as the outer atoms, also abides by the octet rule you may have to rearrange the placement of electrons, which may lead to double bonds, triple bonds and lone pairs of electrons (unbonded electrons)
If the Lewis structure is for an ion remember to draw square brackets around the complete Lewis structure and show the charge. The charge will affect the number of valence electrons for the ion. Negatively charged electron has extra electrons, whereas positively charged ions have less electrons.
If the Lewis structure is for an ion remember to draw square brackets around the complete Lewis structure and show the charge. The charge will affect the number of valence electrons for the ion. Negatively charged electron has extra electrons, whereas positively charged ions have less electrons.
Examples of simple Lewis Structures
Examples of simple Lewis Structures
Relevant for Level 2 Chemistry
Relevant for Level 2 Chemistry
Examples of Lewis structures for some polyatomic ions
Examples of Lewis structures for some polyatomic ions
- More relevant for Level 3 Chemistry
RESONANCE
RESONANCE
In the examples above the Nitrate ion (NO3- ) Lewis structure has a double bond between the Nitrogen and one Oxygen. This double bond could be between the Nitrogen and any of the oxygens. Multiple Lewis structures could be drawn for the same molecule (in NO3- , case there are 3 possible); they are equivalent; this is called resonance. Atoms have not been moved, only electrons.
In the examples above the Nitrate ion (NO3- ) Lewis structure has a double bond between the Nitrogen and one Oxygen. This double bond could be between the Nitrogen and any of the oxygens. Multiple Lewis structures could be drawn for the same molecule (in NO3- , case there are 3 possible); they are equivalent; this is called resonance. Atoms have not been moved, only electrons.
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