water

• Atoms join via bonds to form molecules. Water molecules consist of 2 hydrogen molecules bonded covalently to an oxygen molecule.
• Oxygen and hydrogen do not share electrons equally in a covalent bond. The atom with the greater share of electrons will be slightly negative (δ-). The other atom will be slightly positive (δ+ ). When this happens the molecule is polar
• Water is a polar molecule. The oxygen nuclei has a δ- charge, and the hydrogen nuclei has a δ+ charge.
• As water is polar, the positive and negative regions interact and attract each other to form hydrogen bonds. Hydrogen bonds are relatively weak but contribute to the many properties water molecules have that make them so important to living organisms.
• •Water is a polar molecule composed of one oxygen atom and two hydrogen atoms. Water is a polar molecule as it has regions of both negativity and positivity

  •In water the oxygen is slightly negative (δ-) and the hydrogen is slightly positive (δ+)

  •Water molecules can weakly interact with each other due to the presence of hydrogen bonds.
• The specific heat capacity of a substance is the amount of thermal energy required to raise the temperature of 1kg of that substance by 1°C. Water’s specific heat capacity is 4200 J/kg°C

  This is due to the many hydrogen bonds present in water. It takes a lot of thermal energy to break these bonds and a lot of energy to build them, thus the temperature of water does not fluctuate greatly
• Advantages of high specific heat capacity:

  •Provides suitable habitats

  •Maintains a constant temperature

  •Maintaining temperatures that are optimal for enzyme activity

  •Water in tissue fluid also plays an important regulatory role in maintaining a constant body temperature
• Water is very efficient as a transport medium. Cohesion between water molecules means that molecules stick together. Effects of adhesion and cohesion result in capillary action and also allow for surface tension.
• Adhesive – molecules will stick to surfaces

  Cohesive – molecules will ‘stick to each other
• As water is a polar molecule many ions and covalently bonded polar substances will dissolve in it. This allows chemical reactions to occur within cells as dissolved solutes are more chemically reactive when they are free to move about.
• Water acts as a coolant, helping to buffer temperature changes in chemical reactions. This is because of the large amount of energy needed to overcome hydrogen bonding. Maintaining constant temperatures is important as enzymes have a narrow temperature range
• When water turns to ice it is less dense. This is because of hydrogen bonds between molecules. As water is cooled below 4°C the hydrogen bonds fix the polar molecules slightly further away than in other molecules in a liquid state. The leaves a giant, rigid, but open, structure, resulting in a solid that is less dense than liquid water.
• explain why water is suitable as a habitat for so many organisms.

  • Water is stable and provides a constant environment

  • Ice floats- insulating layer in aquatic environments.

  • Surface tension supports small insects such as pond skaters