Intersection 4
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M. Intersection 4. 9/26/06 Reading: 8.6 bond length p 348-351 8.10 exceptions p 363-366. The Cutting Edge Science at the Extent of our Knowledge Oct 9 th 6:00 – 7:30 PM Information Storage: DNA and Transistors Attendance Optional. M. Outline. Concept Questions Lewis Structures

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Intersection 4

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Intersection 4

M

Intersection 4

9/26/06

Reading: 8.6 bond length p 348-351

8.10 exceptions p 363-366

The Cutting Edge

Science at the Extent of our Knowledge

Oct 9th 6:00 – 7:30 PM

Information Storage: DNA and Transistors

Attendance Optional


Outline

M

Outline

  • Concept Questions

  • Lewis Structures

  • Bond Length

  • Ethics


Question 1

M

Question 1

What is the approximate number of carbon atoms it would take placed next to each other to make a line that would cross this dot: •

  • 4

  • 200

  • 30,000,000

  • 6.02 x 1023


Question 2

A

Question 2

Following is a list of properties of a sample of solid sulfur:

  • Brittle, crystalline solid.

  • Melting point of 113oC.

  • Density of 2.1 g/cm3.

  • Combines with oxygen to form sulfur dioxide

    Which, if any, of these properties would be the same for one single atom of sulfur obtained from the sample?

  • i and ii only.

  • iii and iv only.

  • iv only.

  • All of these properties would be the same.

  • None of these properties would be the same.


Find the molecular weight of

M

Find the Molecular Weight of:

Methane CH4

C 12.011 g/mol (*1)

H 1.007 g/mol (*4)

CH4 16.039 g/mol

Cholesterol C27H46O


Question 3

M

Question 3

Which of the following are true about 18.013 grams of water H2O :

a) Contains 2 hydrogen atoms and 1 oxygen atom

b) Contains 2 moles of hydrogen atoms and 1 mole of oxygen atoms

c) Contains 1 mole of water molecules

d) Is 66.7% hydrogen by weight

e) Contains 6.02 x1023 water molecules


Question 4

M

Question 4

Which of the following samples could be methane, CH4?  A sample that contains:

(a) 25% hydrogen by weight; 75% carbon by weight

(b) 4.0 g of H atoms and 1.0 g of C atoms

(c) 0.40 mole of H atoms and 1.0 x 1023 C atoms

(d) 0.40 mole of H2 molecules and 0.20 moles of C atoms


Question 5

A

Question 5

True or False? When a match burns, some matter is destroyed.

  • True

  • False

    What is the reason for your answer to question 3?

  • This chemical reaction destroys matter.

  • Matter is consumed by the flame.

  • The mass of ash is less than the match it came from.

  • The atoms are not destroyed, they are only rearranged.

  • The match weighs less after burning.


Lewis structures

Lewis Structures

H3O+

Formal charge = # valence electrons -# assigned electrons

Count valence electrons:

H 3 * (1) = 3

O 1 * (6) = 6

- 1

8 valence e-

Assigned electrons:

Nonbonding electrons + 1 e- from each bond

Sum of formal charges = charge of molecule


Intersection 4

SCN-

Note: Usually central atom is least electronegative

16 valence e-

N 3.0; S 2.5


Rules for lewis structures

Rules for Lewis Structures

  • Count valence electrons

  • Select central atom; draw in bonds to connect atoms

  • Fill octets with remaining electrons

  • If octets cannot be filled, increase bond order

  • Repeat octet filling and bond order increase until satisfied

  • Minimize formal charges

  • Double check


Draw the lewis structure for cyanate nco

A

Draw the Lewis Structure for Cyanate NCO-

  • Formal charge rules

    • The smaller the better

    • Negative formal charges should reside on the more electronegative atom

    • Avoid like charges on adjacent atoms


Bond order

Bond Order

1.5

1.33


Is there more than one lewis structure for so 4 2

A

Is there more than one Lewis structure for SO4-2?


Draw the lewis structures for the following molecules

A

Draw the Lewis Structures for the Following Molecules

  • BH3

  • SF6

  • PCl5

  • NO


Group 3

A

Group 3


Expanded octet

A

Expanded Octet

An expanded octet can be achieved with atoms that have d-orbitals in their valence shell.


Intersection 4

A

You must have an atomic orbital in the valence shell for every bond that you make.

You may not use all valence atomic orbitals to make a bond (ex, borane, water, sulfur hexafluoride.)


Radicals

A

Radicals


Exam 1

A

Exam 1

  • Tuesday, October 3

  • 8-10pm CHEM 1400

    • Material through Friday 9/29

    • Non-programmable calculator

    • Practice problems posted on-line


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