# The Geometry of Molecules

## Presentation on theme: "The Geometry of Molecules"— Presentation transcript:

The Geometry of Molecules
Investigation 7B The Geometry of Molecules

Why isn’t water a linear molecule?
Structural diagram: This molecule looks like it should be “straight” or linear… H O H … but it really has a bent shape Why isn’t water a linear molecule? Investigation 7B: The Geometry of Molecules

H O H Lone electron pairs on the oxygen atom take up space too!
Structural diagram: This molecule looks like it should be “straight” or linear… H O H … but it really has a bent shape Lone electron pairs on the oxygen atom take up space too! Investigation 7B: The Geometry of Molecules

Part 1: Linear and bent molecules
Build these five molecules. Compounds made of only 2 atoms are typically bent in shape. Compounds made of only 3 atoms are typically linear in shape. Investigation 7B: The Geometry of Molecules

Part 1: Linear and bent molecules
Name two other elements which would likely form a bent molecule when bound with two hydrogen atoms. Create two other linear molecules. What elements do they contain? Remind students that elements in the same column (or group) in the periodic table have the same number of valence electrons. This means that they have similar bonding patterns. Acetylene for example is a linear molecule (with a triple bond between the two carbons). Note that this question differs from the one in the lab manual. Investigation 7B: The Geometry of Molecules

Real molecules are not flat but have 3-dimensional forms.
Investigation 7B: The Geometry of Molecules

Do these two molecules have the same shape?
Part 2: Trigonal planar and trigonal molecules Build the following molecules. Do these two molecules have the same shape? Investigation 7B: The Geometry of Molecules

Part 2: Trigonal planar and trigonal molecules
Which of these molecules has a trigonal pyramidal shape? Can you explain why? Which of these molecules has a trigonal planar shape? Can you explain why? Name another element which would combine with three hydrogen atoms to make a trigonal molecule. Investigation 7B: The Geometry of Molecules

Part 2: Trigonal planar and trigonal molecules
Investigation 7B: The Geometry of Molecules

Carbon Carbon can donate 4 electrons… 1s22s22p2 4 valence electrons
Lewis dot diagram for carbon Carbon can donate 4 electrons… Investigation 7B: The Geometry of Molecules

Carbon Carbon can donate 4 electrons… … or gain 4 electrons. 1s22s22p2
4 valence electrons Lewis dot diagram for carbon Carbon can donate 4 electrons… … or gain 4 electrons. Investigation 7B: The Geometry of Molecules

Part 3: Molecules with hydrogen and carbon
Build the following molecules. Investigation 7B: The Geometry of Molecules

Part 3: Molecules with hydrogen and carbon
Which of these molecules (if any) is planar? Which of these molecules (if any) is linear? Which of these molecules (if any) is tetrahedral? A tetrahedron is a pyramid with four triangular sides. Which of these molecules (if any) is a ring? Investigation 7B: The Geometry of Molecules

Part 4: Molecules with nitrogen and oxygen
Many important molecules contain nitrogen and oxygen atoms. Investigation 7B: The Geometry of Molecules

Part 4: Molecules with nitrogen and oxygen
Many important molecules contain nitrogen and oxygen atoms. These questions are phrased a bit differently in the lab manual. Name two instances in these molecules where you find a tetragonal form. What element is central to this form? Name two instances in these molecules where you find a trigonal form. What element is central to this form? Investigation 7B: The Geometry of Molecules

Part 4: Molecules with nitrogen and oxygen
Many important molecules contain nitrogen and oxygen atoms. c. Describe what is similar between methanol (wood alcohol) and ethanol (grain alcohol). Investigation 7B: The Geometry of Molecules

Part 4: Molecules with nitrogen and oxygen
Many important molecules contain nitrogen and oxygen atoms. d. Amines are nitrogen-bearing compounds, often with very strong odors. Which of these compounds are amines? Investigation 7B: The Geometry of Molecules

(active ingredient in Tylenol)
The function of a molecule depends on its 3-dimensional shape. Ascorbic acid (vitamin C) Acetaminophen (active ingredient in Tylenol) Investigation 7B: The Geometry of Molecules