Drawing Lewis Structures

Get a whiteboard and a marker!!!

How to Draw Lewis Structures

Rules for Lewis Structures: • • 1 . Count the valence electrons for all atoms.

2. Put the least electronegative atom in the center. (H always goes on the outside) • • • • 3. Assign 2 electrons to each bond.

4. Complete octets on outside atoms.

5. Put remaining electrons in pairs on central atom.

6. If central atom does not have an octet, move electrons from outer atoms to form double or triple bonds.

Rules for Lewis Structures: CH 3 I Determine the type and number of atoms in the molecule.

How many carbon?

Rules for Lewis Structures: CH 3 I Determine the type and number of atoms in the molecule.

How many carbon? 1 How many iodine?

Rules for Lewis Structures: CH 3 I • 1 . Determine the type and number of atoms in the molecule.

How many carbon? 1 How many iodine? 1 How many Hydrogen?

Rules for Lewis Structures: CH 3 I • 1 . Determine the type and number of atoms in the molecule.

How many carbon? 1 How many iodine? 1 How many Hydrogen? 3

Rules for Lewis Structures: • 1. Determine the total number of valence electrons in the atoms to be combined.

C I H 1 x 4 e = 4 e 1 x 7 e = 7 e 3 x 1e = 3 e 14 e

Rules for Lewis Structures: • • 2 . Arrange the atoms to form a skeleton structure for the molecule. If carbon is present, it is the central atom. If not, the least-electronegative atom is central (except Hydrogen – it is never central). H ..

H : C : I ..

H

Rules for Lewis Structures: 3.

Assign 2 electrons to each bond. 4.

Complete octets on outside atoms

Rules for Lewis Structures: 5.

Put remaining electrons in pairs on central atom.

6.

If central atom does not have an octet, move electrons to form double or triple bonds. • We have 14 valence electrons – the correct number!!

Try NH 3 (Ammonia)

Try NH 3

Try H 2 S (Hydrogen sulfide)

Try H 2 S

Try CH 2 O (Formaldehyde)

Try CH 2 O

• • PBr 3 N 2 H 2 Try 2 more: