1. what is a hydrogen bond? indicate where the hydrogen bond occurs in the following figure. (figure of h₂o and another molecule) 2. use morphine and endorphins as examples to explain why molecular shape is crucial in biology. 3. study the water molecules below. on the central molecule, label oxygen (o) and hydrogen (h). now, add + and - signs to indicate the charged regions of each molecule. then, indicate the hydrogen bonds. (figure of water molecules) 4. water is considered a polar molecule. what does this mean?

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### Question 1
# Brief Explanations:
A hydrogen bond is a weak electrostatic attraction between a hydrogen atom covalently bonded to a highly electronegative atom (like O, N, F) and another electronegative atom. In the figure (water $ \ce{H2O} $ and ammonia $ \ce{NH3} $), the hydrogen bond occurs between the partially positive $ \ce{H} $ of $ \ce{H2O} $ and the partially negative $ \ce{N} $ of $ \ce{NH3} $ (or between $ \ce{H} $ of $ \ce{NH3} $ and $ \ce{O} $ of $ \ce{H2O} $, depending on orientation).
# Answer:
A hydrogen bond is a weak attraction between a H atom (bonded to O/N/F) and an electronegative atom. In the figure, it occurs between the $ \delta^+ $ H of $ \ce{H2O} $ and $ \delta^- $ N of $ \ce{NH3} $ (or vice versa).

### Question 2
# Brief Explanations:
Molecular shape determines function. Endorphins (natural) and morphine (drug) have similar shapes. Endorphins bind to brain receptors to reduce pain. Morphine, with a matching shape, also binds to these receptors, mimicking endorphins’ pain - relieving effect. Different shapes would mean no binding, so shape is key for molecular interactions (like ligand - receptor binding).
# Answer:
Molecular shape is crucial as it determines if a molecule can interact (bind) with others. Endorphins (natural pain - relievers) and morphine (pain - relieving drug) have similar shapes. This allows both to bind to the same brain receptors, enabling morphine to mimic endorphins’ pain - reducing function. A different shape would prevent binding and the associated biological effect.

### Question 3
# Brief Explanations:
1. **Label Atoms**: In a water molecule ($ \ce{H2O} $), the central (and all) $ \ce{H2O} $ has one O (red, more electronegative) and two H (gray).
2. **Charge Regions**: O is $ \delta^- $ (due to higher electronegativity, pulls electrons), H is $ \delta^+ $ (electrons pulled away).
3. **Hydrogen Bonds**: These are the dashed lines between the $ \delta^+ $ H of one $ \ce{H2O} $ and $ \delta^- $ O of another $ \ce{H2O} $.
# Answer:
- **Oxygen (O)**: Label the red atom(s) as O.
- **Hydrogen (H)**: Label the gray atom(s) as H.
- **Charges**: Mark O with $ \delta^- $, H with $ \delta^+ $.
- **Hydrogen Bonds**: The dashed lines between $ \delta^+ $ H (of one $ \ce{H2O} $) and $ \delta^- $ O (of another $ \ce{H2O} $) are hydrogen bonds.

### Question 4
# Brief Explanations:
A polar molecule has a partial separation of charge (dipole). In $ \ce{H2O} $, O is more electronegative than H. So, O pulls shared electrons closer, making O $ \delta^- $ and H $ \delta^+ $. The molecule has a bent shape, so the dipole moments (from O - H bonds) don’t cancel, resulting in a net dipole (polarity).
# Answer:
A polar molecule (like $ \ce{H2O} $) has a partial charge separation. In water, oxygen (O) is more electronegative than hydrogen (H), so O has a partial negative charge ($ \delta^- $) and H has a partial positive charge ($ \delta^+ $). The bent molecular shape means the bond dipoles (from O - H bonds) don’t cancel, giving the molecule a net dipole (polar nature).

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