smells unit – investigation ii

Smells Unit – Investigation II

Lesson 4:

Eight is Enough

© 2004 Key Curriculum Press.

Unit 2 • Investigation II

Admit Slip

• Draw the Lewis dot structure for the following covalently bonded molecule. Explain how you arrived at your answer.

Cl2 HBr NH3



The Big Question

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



Today’s Objectives:

• Students will be able to:

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


Agenda

Admit Slip

Homework Check/Review

Notes

Classwork

Exit Slip

Product: Notes, Worksheet, Exit Slip

Homework: Back of Packet!



Homework ReviewDraw structural formulas for the following molecular formulas.

1. C4H10O

2. C5H10O with one C-O double bond



3. C3H4O2 with two C-O double bonds

4. C4H9N with one C-N double bond



5.C3H5N with one C-N triple bond

Draw Lewis Dot symbols/ structures of:

6. Se 7. Br



8. As

9. CH4

10. H2O




Cl Cl+ Cl Cl

Octet Rule 12 / 10 / 13

When bonding two atoms, 1 unpaired electron from each atom comes together with another unpaired electron to form a bond (2 shared electrons).


• The octet rule states that atoms tend to form bonds by sharing valence electrons until eight (8) valence electrons surround each atom.…

…except for Hydrogen, H!

• Hydrogen will only have (2) valence electrons after it bonds.

• When the atoms have 8 (or 2) valence electrons, they are stable like the noble gases.




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

1. Look at your drawings of Br2, H2S, PH3, and SiH4 above:a) How many electrons surround the Br atom on the left, including the ones it’s sharing?

b) How many electrons surround the Br atom on the right, including the ones it’s sharing?



c) How many electrons surround S, P, and Si?

d) How many electrons does each H have access to in these molecules?

2. How many chlorine atoms would bond covalently with a single carbon atom? Explain. (Hint: Use Lewis dot symbols to help you figure this out.)

3. Create a drawing representing the bonding of chlorine atoms with a single carbon atom. Start with the Lewis dot symbol for carbon.



4. How many fluorine atoms would bond covalently with a single phosphorus atom? Explain.

4. Create a drawing representing the bonding of fluorine atoms with a single phosophorus atom. Start with the Lewis dot structure of phosphorous.

4. Draw the structural formula of the molecule you created using Lewis dots symbols in question 5.

5. What is the molecular formula of the molecule you created in question 5?



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).



Exit Slip

• Which of the following formulas satisfy the HONC 1234 rule?

• Which of the following formulas satisfy the octet rule?

• Which of the following formulas represents a stable compound 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.

smells unit – investigation ii

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