| Why are the electrons in H2O not shared equally? | because oxygen has a higher electronegativity = attracts the electrons more strongly
electrons orbit closer to the oxygen atom = polarity
=permanent dipole |
| why is water polar? | because of the slight charge difference across the different poles
oxygen is slightly negative
hydrogen atoms are slightly positive |
| What does the charge difference allow water to do? | form weak polar associations with other polar molecules
slightly negative attracts the slightly positive poles of other molecules
vice versa |
| When does a hydrogen bond form? | when the slightly positive hydrogen from H2O is attracted to a slightly negative F, O, N atom of another molecule |
| Why are hydrogen bonds stronger than other polar associations? | because of the high electronegativity of F, O and N |
| How does water bond with other water molecules? | between a + hydrogen and a - oxygen of two molecules |
| What gives water its special properties? | the intermolecular bonding between water molecules |
| Why can water absorb so much heat before changing state? | because of extensive hydrogen bonding between water molecules
H-bonds need to be broken = needs heat energy |
| What are the 3 properties of water? | thermal properties - water can absorb a lot of heat before changing state because breaking the hydrogen bonds is needed
cohesive / adhesive properties - water sticks to other water molecules (cohesion) and charged substances (adhesion)
Solvent properties - water dissolves polar and ionic substances = competing polar associations to draw materials apart |
| Why is water a good place for living organisms? | temperature changes slowly = maintenance of constant conditions |
| Comparing Methane (CH4) with water | H20 weight = 18 dalton
CH4 weight = 16 dalton
both have tetrahedral orbital forms but water is bent because of unbonded electron pairs |
| What is sweating? | evaporation of water to cool down |
| How does sweating work? (4) | change of water from liquid = vapour needs energy
energy comes from the skin's surface when its hot
when water evaporates skin is cooled
because water has a high SHC = absorbs a lot of thermal energy before evaporating
water - highly effective coolant |
| What are the cohesive properties of water? | same molecules stick together
forms hydrogen bonds w other water molecules |
| What are the adhesive properties of water? | different molecules stick together by forming intermolecular associations with polar and charged molecules |
| How does the cohesive properties explain surface tension? | hydrogen bonding between water molecules helps the liquid to resist low levels of external force
makes the water dense enough for small organisms to move along its surface |
| How does the adhesive properties explain the capillary action? | attraction to charged or polar surfaces makes water to flow against gravity = capillary action
needed for water to be transported up plant stems by transpiration |
| Why can water dissolve so many substances? | can dissolve any substance that has charged particles (ions) or electronegative atoms (polarity)
because the polar attraction of a large amount of water molecules = weaken intramolecular forces (ionic) =
disassociation |
| How does hydration occur? | slightly charged regions of the hydrogen atoms and the oxygen atoms surround atoms with an opposing charge
= forms dispersive hydration shells |
| what does hydrophilic mean? | substances that freely associate and readily dissolve in water
all polar molecules and ions |
| What does hydrophobic mean? | substances that don't dfeely associate or dissolve in water
large non polar molecules (fats and oils) |
| What are water soluble substances that travel in our body? | Sodium chloride (NaCl): ionic transported in blood
Oxygen: small amounts are soluble in water transported in haemoglobin in red blood cells
Glucose: hydroxyl groups (-OH) associates with water so it travels in the blood
Amino Acids: transported in an ionized state (either amine or carboxyl group is charged) |
| What are water insoluble substances that travel in our body? | lipids (fats and cholesterol): non polar and hydrophobic so it does not dissolve in water
form complexes with proteins (lipoproteins) = to go through bloodstream
hydrophilic parts of proteins, cholesterol and phospholipids shield internal hydrophobic parts |
