2.2 WATER Flashcards
water is made of…
two hydrogen atoms covalently bonded to form an oxygen atom. this involves the sharing of electrons, but they are not shared equally between atoms.
oxygen attracts the electrons…
more strongly because they have a higher electronegativity
the shared electrons orbit closer to the oxygen atom than the hydrogen atoms, resulting in polarity l
why is water described as polar
it has a slight charge difference across the different poles of the molecule: the oxygen atom is slightly negative while the hydrogen atoms are slightly positive.
what does the charge difference in water allow
water can form weak associations with other polar molecules. the slightly negative poles will attract the slightly positive poles of other molecules and vice versa.
how are hydrogen bonds formed
when a positive hydrogen atom is attracted to a negative fluorine, oxygen, or nitrogen atom of another molecule, it forms a hydrogen bind. hydrogen bonds are stronger than other polar associations due to high electronegativity of F, O, and N
properties of water
thermal properties - can absorb a lot of heat before changing state
cohesive / adhesive properties - will stick to other molecules via cohesion and to charged substances via adhesion
solvent properties - water dissolves polar and ionic substances
why is water a good medium for living organisms
it is slow to change temperature and thus supports the maintenance of constant conditions (internal and external)
water vs methane
water is polar and can form intermolecular hydrogen bonds, whilst methane is non-polar and can form weak dispersion forces between its molecules.
water has a higher melting and boiling point
water has a higher specific heat capacity
water has a higher heat of vaporization
water has a higher heat of fusion
the evaporation of water as sweat
the change of water from liquid to vapour requires an input of energy. this energy comes from the surface of the skin where it is hot, therefore when the sweat evaporates, the skin is cooled. because water has a high specific heat capacity, it absorbs a lot of thermal energy before it evaporates. thus water functions as a highly effective coolant, making it the principal component of sweat
cohesion and cohesive properties explain what
cohesion is the ability of molecules to stick together. water will form hydrogen bonds.
cohesive properties of water explain surface tension. hydrogen bonding between the water molecules allow the liquid to resist low levels of external force. the high surface tension of the water makes it sufficiently dense for certain smaller organisms to move along its surface
