Give students step-by-step practice drawing Lewis dot structures with this free printable chemistry worksheet.
Try these Lewis structure questions online before (or after) you print the worksheet. Click an answer to check it, or open "Show answer" for the explanation.
How many valence electrons are in CH₃Br?
Answer: 14. 4 (C) + 3 × 1 (H) + 7 (Br) = 14 valence electrons.
How many valence electrons are in NH₄⁺?
Answer: 8. 5 (N) + 4 × 1 (H) − 1 for the positive charge = 8.
Which atom is the central atom in HOBr?
Answer: O. H can only form one bond, so O sits in the middle: H–O–Br.
How many lone pairs are on the central atom of NBr₃?
Answer: 1. N has 5 valence electrons. Three go into N–Br bonds and the last 2 form one lone pair.
How many lone pairs are on the central atom of SBr₂?
Answer: 2. S has 6 valence electrons. Two go into S–Br bonds, leaving 4 electrons, or 2 lone pairs.
What kind of bond joins the two C atoms in C₂H₃F (fluoroethene)?
Answer: double. With single bonds only, one C would have just 6 electrons. A C=C double bond gives both carbons an octet.
How many electrons does a hydrogen atom need in a Lewis structure?
Answer: 2. Hydrogen follows the duet rule: one bond (2 electrons) and no lone pairs.
How do you show the charge on a polyatomic ion like HS⁻ in a Lewis structure?
Answer: Put the structure in square brackets with the charge outside. The charge belongs to the whole ion, so the structure goes in brackets with the charge at the top right.
Each statement below has an error. Work out the correct version, then check your answer.
CH₃OH has no lone pairs on O.
O has 2 lone pairs. O has 6 valence electrons: 2 are used in bonds (to C and H), so 4 remain as 2 lone pairs.
O₂ has a single bond with 3 lone pairs on each O.
O₂ has a double bond (O=O) with 2 lone pairs on each O. O₂ has only 12 valence electrons; the single-bond drawing uses 14.
AsH₄⁺ has a lone pair on As.
AsH₄⁺ has no lone pair on As. 5 + 4 − 1 = 8 electrons, which all go into the four As–H bonds.
C₂²⁻ has 8 valence electrons.
C₂²⁻ has 10 valence electrons. 2 × 4 = 8, plus 2 for the 2− charge.
Want more practice? Download the free printable worksheet and answer key above.