Drawing Lewis Structures

Flashcards covering the rules for drawing Lewis structures for molecules and ions.

Step 1 of drawing Lewis Structures

Place the least electronegative element at the center of the molecule.

Hydrogen in Lewis Structures

It can only form one bond and cannot be the central atom.

Carbon in Lewis Structures

It is always at the center and can form chains.

Step 2 of drawing Lewis Structures

Count the number of valence electrons for each atom, adding or subtracting electrons based on the ion's charge.

Step 3 of drawing Lewis Structures for Polyatomic Ions

Draw a square bracket around the Lewis formula and write the overall charge outside the bracket at the top right-hand corner.

Step 4 of drawing Lewis Structures

Draw one bond from the central atom to all surrounding atoms.

Step 5 of drawing Lewis Structures

Distribute the remaining electrons as lone pairs to each surrounding atom until they have a full octet.

Exceptions to the Octet Rule

H, Be, and B

Final step for electron distribution

Add any remaining electrons to the central atom.

Period 2 Central Atom Electron Limit

If the central atom is from period 2, it cannot have more than eight electrons around it.

Period 3+ Central Atom Electron Capacity

If the central atom is from period 3 or beyond, it can have more than eight electrons around it.

For polyatomic ions, add/subtract electrons based on the charge:

• Negative charge → add electrons

• Positive charge → subtract electrons

Never make double/triple bonds to hydrogen or halogens

like F, Cl, Br, I.