smells unit – investigation ii

Smells Unit – Investigation II

Lesson 3:Connect the Dots

Unit 2 • Investigation II

© 2004 Key Curriculum Press.

ChemCatalyst

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

C H

H

H

H



The Big Question

• How can Lewis dot symbols help us to understand and predict bonding?



You will be able to:

• Draw the Lewis dot symbol for an element and predict how many covalent bonds it will make.



• A covalent bond is a connection that forms between two atoms when those atoms are sharing a pair of electrons between them.

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.

Notes (cont.)

(cont.)



• Nitrogen, with five valence electrons, would be drawn as follows:

N N N N Nstart here

• 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.

Notes (cont.)

(cont.)



C H

H

H

H

CH

H

H

H

CH H

H

H

CH

H

H

H

Notes (cont.)



• 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.

Notes

(cont.)



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.)



C N O F Ne

Si P S Cl Ar

(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.)

(cont.)



CH4 + CH

H

H

H

NH3 +

OH2 +

(cont.)



Making Sense

• Based on what you’ve learned in this lesson, explain why the HONC 1234 rule works.



C HON

CH O N

(cont.)

Notes



• 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.

N H

H

H

lone pair of electrons

bonded pair of electrons

Notes (cont.)



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?



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.


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



The Big Question

• How can we use Lewis dot structures to help draw structural formulas?




• Predict whether a given compound would be stable and likely to be found in nature.



Cl Cl+ Cl Cl

Notes



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.)



Br2 H2S PH3 SiH4

(cont.)

(cont.)



CCl4 C+

Cl

Cl

Cl

Cl

P F+ 3 P

F

FF

P F

F

F

(cont.)



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).



• 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.

Notes



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



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.


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.

N N O O F F



The Big Question

• How do we draw a Lewis dot structure for a molecule?




• Use Lewis dot symbols to draw a possible structure for a C2H4O2 molecule.



Draw Lewis dot symbols for C and two O atoms:

Bring atoms together:

Create double bonds:

C O Oand and

CO O

CO O

Notes



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.)



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

(cont.)



Making Sense

• Explain how HONC 1234 assists you in checking out the structural formulas you create.



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.)



Wrap-Up

• Atoms can form double and triple bonds to satisfy the octet rule.

smells unit – investigation ii

Documents

key curriculum press

valence electrons

lewis dot symbol of

lewis dot symbols

unpaired electrons

lewis dot structure

electron pair

covalent bonds