Smells Unit – Investigation II Lesson 3: Connect the Dots

ChemCatalyst This is a drawing of the structural formula of a methane molecule. The lines represent bonds. Explain what you think a bond is. Unit 2 • Investigation II

The Big Question How can Lewis dot symbols help us to understand and predict bonding? Unit 2 • Investigation II

You will be able to: Draw the Lewis dot symbol for an element and predict how many covalent bonds it will make. Unit 2 • Investigation II

Notes A covalent bond is a connection that forms between two atoms when those atoms are sharing a pair of electrons between them. (cont.) Unit 2 • Investigation II

Notes (cont.) When we draw an atom using dots to represent the valence electrons it is called a Lewis dot symbol. When we draw a molecule using dots to represent the valence electrons it is called a Lewis dot structure. (cont.) Unit 2 • Investigation II

Notes (cont.) Nitrogen, with five valence electrons, would be drawn as follows: Notice that the Lewis dot symbol of nitrogen has three unpaired electrons and one electron pair. This means that nitrogen has three electrons that can potentially be paired up with electrons from other atoms. (cont.) Unit 2 • Investigation II

Notes (cont.) Unit 2 • Investigation II

Notes HONC 1234 is a simple, catchy phrase reminding us about the bonding of hydrogen, oxygen, nitrogen and carbon. This easy-to-remember phrase reminds us how many bonds each element usually makes within a molecule. (cont.) Unit 2 • Investigation II

Activity Purpose: In this lesson you will begin to understand why atoms connect to each other the way they do. You will be introduced to a tool, called Lewis dot symbols, which will assist you in building molecules and predicting how many bonds an element will have. (cont.) Unit 2 • Investigation II

(cont.) C N O F Ne Si P S Cl Ar (cont.) Unit 2 • Investigation II

(cont.) (cont.) Group number IV V VI VII VIII Number of bonds First row elements C N O F Ne Second row elements Si P S Cl Ar (cont.) Unit 2 • Investigation II

(cont.) Unit 2 • Investigation II

Making Sense Based on what you’ve learned in this lesson, explain why the HONC 1234 rule works. Unit 2 • Investigation II

Notes (cont.) Unit 2 • Investigation II

bonded pair of electrons Notes (cont.) Bonded pair refers to a pair of electrons that are involved in bonding between two different atoms. Lone pair refers to a pair of electrons that are not involved in bonding but are paired up within an atom. A single electron is sometimes referred to as an unpaired electron. lone pair of electrons bonded pair of electrons Unit 2 • Investigation II

Check-In Draw the Lewis dot symbol for the element I, iodine. Explain how you arrived at your particular drawing. How many covalent bonds does iodine make? Unit 2 • Investigation II

Wrap-Up A covalent bond is one in which two atoms share valence electrons. In a Lewis dot structure, pairs of electrons that are not bonded are referred to as lone pairs. HONC 1234 indicates how many unpaired electrons are associated with hydrogen, oxygen, nitrogen and carbon. Unit 2 • Investigation II

Smells Unit – Investigation II Lesson 4: Eight is Enough

ChemCatalyst Draw the Lewis dot structure for the following covalently bonded molecule. Explain how you arrived at your answer. Cl2 Unit 2 • Investigation II

The Big Question How can we use Lewis dot structures to help draw structural formulas? Unit 2 • Investigation II

You will be able to: Predict whether a given compound would be stable and likely to be found in nature. Unit 2 • Investigation II

Notes Unit 2 • Investigation II

Activity Purpose: In this lesson you will use Lewis dot structures to create structural formulas of molecules containing elements in addition to H, O, N, and C. You will look for patterns in the number of electrons surrounding each atom in a Lewis dot structure in order to develop further understanding of bonding. (cont.) Unit 2 • Investigation II

(cont.) Br2 H2S PH3 SiH4 (cont.) Unit 2 • Investigation II

(cont.) Unit 2 • Investigation II

Making Sense The noble gases do not form bonds with other atoms (except under very extreme conditions). Explain why you think this might be true (use your Lewis dot structures). Unit 2 • Investigation II

Notes Atoms of most elements are very reactive. They become stable (the opposite of reactive) when they combine with other atoms to form compounds. The more stable a molecule is, the more likely we are to find that it exists in nature. The octet rule states that atoms tend to form bonds by sharing valence electrons until eight valence electrons surround each atom. Unit 2 • Investigation II

Check-In Which of the following formulas satisfy the HONC 1234 rule? Which of the following formulas satisfy the octet rule? Which of the following formulas represent stable compounds we might find in the world around us? a) CH3 b) CH4 Unit 2 • Investigation II

Wrap-Up Elements form bonds by sharing electrons until each atom has the same number of valence electrons as the noble gas in the same row of the periodic table — this is called the octet rule. Unit 2 • Investigation II

Smells Unit – Investigation II Lesson 5: Dots, Dots, and More Dots

ChemCatalyst Here are the structural formulas for N2 (nitrogen gas), O2 (oxygen gas), and F2 (fluorine gas). Draw the Lewis dot structures for these three molecules. Unit 2 • Investigation II

The Big Question How do we draw a Lewis dot structure for a molecule? Unit 2 • Investigation II

You will be able to: Use Lewis dot symbols to draw a possible structure for a C2H4O2 molecule. Unit 2 • Investigation II

Notes Draw Lewis dot symbols for C and two O atoms: Bring atoms together: Create double bonds: Unit 2 • Investigation II

Activity Purpose: In this lesson you will work to create structural formulas for various molecules. You will start with the Lewis dot structures of individual atoms. These atoms can then be arranged in more than one way to create molecules. Finally, structural formulas will be translated from the Lewis dot representations. (cont.) Unit 2 • Investigation II

(cont.) Start with these atoms… Draw the Lewis structure for the starting atoms Add hydrogen atoms to satisfy the octet rule How many H’s are needed? Draw the structural formula for the molecule Write the molecular formula for the molecule 2 carbon atoms bonded together 1 carbon atom and 1 oxygen atom 1 carbon atom and 1 nitrogen atom 1 carbon atom and 2 oxygen atoms Unit 2 • Investigation II

Making Sense Explain how HONC 1234 assists you in checking out the structural formulas you create. Unit 2 • Investigation II

Check-In We know two things about a certain molecule. We know that its molecular formula is C2H4O2 and we know that it has one C=O in it. Using Lewis dot symbols and the octet rule to guide you, draw at least one possible structure for this molecule. (There are a total of three possible.) Unit 2 • Investigation II

Wrap-Up Atoms can form double and triple bonds to satisfy the octet rule. Unit 2 • Investigation II