BSC1010 Lecture 3 (recorded)

Polarity of Water Molecules

• Water is a polar molecule due to uneven distribution of charge.

  • Oxygen Atom: Slightly negative charge due to shared electrons.

  • Hydrogen Atoms: Each has a slight positive charge.

  • Overall charge of water is neutral; compensates with positive and negative areas.

Hydrogen Bonds

• Hydrogen bonds form between polar molecules, such as water.

  • Formation: Slightly positive hydrogen of one water molecule attracts the slightly negative oxygen of another.

  • Importance: These weak attractions dictate many properties of water.

Properties of Water

• Cohesion: Water molecules stick together, contributing to capillarity in plants.

• Adhesion: Water molecules can also stick to other substances, helping in processes like water movement in plants.

• High Specific Heat: Water requires a lot of energy to change temperature, moderating climate and bodily temperatures.

• Less Dense as Ice: Ice floats on water because solid water has more air spaces among molecules than liquid water.

Dissociation of Water

• Water can dissociate into hydroxide ions (OH-) and hydrogen ions (H+), crucial for acid-base balance in solutions.

pH Scale

• The scale measures hydrogen ion concentration in a solution.

• Acidic Solutions: Low pH (e.g., lemon juice at pH 2).

• Neutral Solution: Pure water at pH 7, with equal H+ and OH- concentrations.

• Basic Solutions: Higher pH (e.g., baking soda at pH 9).

Buffers

• Buffers help maintain stable pH levels in biological systems by accepting/releasing hydrogen ions as needed.

  • Example: Carbonic Acid/Bicarbonate System in the human body helps maintain blood pH.

  • Important for preventing drastic changes that can disrupt biological functions.

Types of Chemical Bonds

• Covalent Bonds: Strongest in biological systems; involve sharing of electron pairs.

• Ionic Bonds: Formed from the transfer of electrons and attraction of charged ions.

• Van der Waals Forces: Weak interactions that occur due to transient partial charges.

Importance in Biology

• Hydrogen bonds facilitate the structure of DNA and proteins, proving essential in biological functions.

• Molecules can have various functional groups affecting reactivity and interactions.