Water

• Structure of water molecule: 2 hydrogen atoms and 1 oxygen atom

  
• Oxygen has a greater electronegativity (the tendency for an atom to attract shared electrons in a molecule) causing the shared electrons to orbit closer to the oxygen atom than the hydrogen atoms. This creates a slight difference in charge, which we call a polar molecule (a molecule with regions of different charges).
• Water is a dipolar molecule because it has two regions of charge.We represent the slight charges with the symbol delta. The oxygen is delta negative, because it has greater electronegativity and the electrons (which have a negative charge) are closer to it. The hydrogens are delta positive because it has less electronegativity, so the electrons are further away.
• Becuase of water’s polarity, intermolecular bonds between water molecules can form. The type that can form are called hydrogen bonds.

  The slight negative oxygen is attracted to the slight positive hydrogen on another molecule. This creates a hydrogen bond between the molecules.

  It is these hydrogen bonds that give water its properties which makes it such an essential part of life on earth
• Properties of Water

  • Thermal properties – Water can absorb much heat before changing state (requires breaking of hydrogen bonds)
  • Cohesive / adhesive properties – Water will ‘stick’ to other water molecules (cohesion) and charged substances (adhesion)
  • Solvent properties – Water dissolves polar and ionic substances (forms competing polar associations to draw materials apart)
• 1. Explain the unique structure of a water molecule, including the arrangement of its atoms and the type of bond that holds them together: A water molecule (H2O) consists of two hydrogen atoms covalently bonded to one oxygen atom. The oxygen atom is more electronegative, leading to a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. This polarity results from the unequal sharing of electrons, forming polar covalent bonds within the molecule.
• Water's high surface tension allows it to form a "skin" on its surface, enabling small organisms like water striders to "walk" on water. Its high heat capacity helps regulate temperature in aquatic environments, preventing rapid temperature fluctuations that could harm aquatic life. Additionally, water's versatility as a solvent is crucial for the dissolution and transport of ions, polar molecules, and nutrients in living organisms, facilitating biochemical reactions and nutrient uptake.
• 1. Water's high heat capacity allows it to absorb and store heat energy, making it an effective coolant in biological systems. In organisms like humans, sweat is produced, which evaporates and carries away heat, helping to regulate body temperature. Additionally, in plants, transpiration (the loss of water vapor) cools the plant and aids in the transport of water and nutrients.
• Cohesion in water refers to the attractive forces between water molecules, resulting in their tendency to stick together. This property is crucial for the survival of plants as it allows water to be transported upward from the roots to the leaves via the xylem vessels, creating a continuous water column. Without cohesion, water would not be able to defy gravity and reach the upper parts of tall trees, affecting their growth and nutrient uptake. Water is often described as the "universal solvent."
• Water's designation as the "universal solvent" stems from its ability to dissolve a wide range of substances. Its polar nature allows it to interact with and solvate ionic compounds and polar molecules. An example of its indispensability as a solvent in biology is its role in blood, where it dissolves gases like oxygen and carbon dioxide, ions like sodium and chloride, and various nutrients and waste products. This enables the transport of vital substances within the circulatory system, ensuring the proper functioning of organisms.
• Water is a dipolar molecule. What does this mean? The molecule has two different regions with opposite charges. What causes this? Oxygen has a higher electronegativity than hydrogen and attracts the shared electrons, making the oxygen atom slightly negative, and the hydrogen atoms slightly positive.
• The main hypothesis for the origins of water on earth is that water came from extraplanetary objects (i.e. comets and asteroids). This is strongly supported by evidence comparing the remains of asteroids and the water currently on earth. They compare the deuterium to hydrogen ratio in water.  Deuterium is an isotope of hydrogen, meaning it is the same element but has an added neutron. 
• The Deuterium:Hydrogen ratio on earth is the same (or very similar to) the ratio from the remnants of old asteroids, suggesting it originated from there.The water remained on earth because of gravity, and the distance from the sun means that the temperature on earth is lower than that needed to vaporise it, so the earth retained large bodies of water.
• The difference between Hydrogen and Deuterium is deuterium has a extra neutron

  
• The nucleus of the oxygen atom is more attractive to electrons than the nucleus of the hydrogen atom. There is unequal sharing of electrons. This causes hydrogen to be partially positive charge and oxygen to be partially negative charge.
• Substances which dissolve in water are known as hydrophilic
• Which of the following is a hydrophobic molecule? Trigylceride
• Capillary action in plant cell walls and the movement of water through soil is explained by which property? Adhesion
• The transport of water up the xylem in plants depends on which property? Cohesion
• Cohesion depends on the hydrogen bonding between hydrogen and oxygen in a different water molecule
• The black-throated loon (Gavia arctica) spends much of its time flying but can also swim underwater and dive to catch fish. Solid bones, compression of air in its feathers and in the lungs are necessary because water produces more buoyancy than air
• he high specific heat capacity of water enables large expanses of water, e.g. a lake habitat to maintain a relatively stable temperature
• Water is often called a universal solvent, but why is this statement incorrect? Water does not dissolve organic compounds such as lipids