Periodic Table Study Guide How to Draw Lewis

Periodic Table Study Guide How to Draw Lewis Structures www. middleschoolscience. com 2008

Objective/Warm-up SWBAT draw Lewis dot structures. How many valence electrons do each of the following elements have? Ca K O S C Br N

Groups Review Group 8 = 8 electrons Group 1 = 1 electron Group 2 = 2 electrons 3, 4, 5, 6, 7 Except for He, it has 2 electrons • Each column is called a “group” • Each element in a group has the same number of electrons in their outer orbital. www. chem 4 kids. com • The electrons in the outer shell are called “valence electrons”

Lewis Structures Find out which group (column) your element is in. This will tell you the number of valence electrons your element has. You will only draw the valence electrons. www. chem 4 kids. com

Lewis Structures 1) Write the element symbol. 2) Carbon is in the 4 th group, so it has 4 valence electrons. C 3) Starting at the right, draw 4 electrons, or dots, around the element symbol.

Review-Octet Rule Atoms bond in order to have 8 valence electrons. Exception: Hydrogen only needs 2 valence electrons to be complete.

Rules for drawing Lewis Dot Structures 1. Count all the valence electrons for your atoms. 2. Draw the first atom (Second atom if the first is Hydrogen) listed in the center, then connect all other atoms to the center atom with single bonds. 3. Each bond counts as 2 electrons. 4. Complete any octets with remaining electrons. Example: CH 2 Cl 2 C= 4 valence H=1 x 2 valence Cl=7 x 2 valence Total=20 valence

Try these… CH 4 NF 3

Double and triple bonds What happens if you don’t have enough electrons? Example: CO 2 Make double or triple bonds.

Try these… OF 2 O 2 N 2 C 2 H 6 C 2 H 4 C 2 H 2 SO 3

Helpful Hints Remember: your Lewis structure may contain multiple bonds (single, double, or triple) When arranging your atoms, atoms are often written in the order in which they are connected in a molecule or ion (C is almost always your central atom; carbon forms 4 bonds)

Examples Draw the dot structure: H 2 O CH 3 Br CS 2 CH 2 O O 3

Closure Explain the steps to writing electron dot structures.