2.2 Water Flashcards
Structure of Water
H2O
2 hydrogen atoms = oxygen atom
covalently bonded
Covalent bonding of H2O described
Unequal sharing of electrons between atoms.
Oxygen has higher electronegativity = which attracts electrons more strongly.
Shared electrons orbit closer to oxygen
Polarity
How different the electrical poles of a molecule are
Polarity of water
Polar; oxygen atom is negative, hydrogen atoms are slightly postive
Charge difference is Dipole
Water polarity purpose
Charge difference (dipole) allows water to form weak associations with other polar molecules
(neg poles attract pos poles, etc.)
Hydrogen bond
When a (+)hydrogen atom is a attracted to a (-)fluorine, oxygen or nitrogen
Covalent bond
Formed by equal sharing of electrons from both atoms
Purpose of dipolairty of water molecule
enables it to form polar associations with other charged molecules (polar or ionic)
Hydrogen bonding of water
Water can form hydrogen bonds with other water molecules
Properties of water
- Thermal properties
- Cohesive / adhesive properties
- Solvent properties
How water has its unique properties
This intermolecular bonding between water. Not seen in other substances
Thermal properties of water
Can absorb a lot of heat before changing state
Requires breaking of hydrogen bonds
Cohesive / adhesive properties
Water sticks to other water molecules (cohesion) and charged substances (adhesion)
Reason of water’s thermal property
- Extensive hydrogen bonding of water molecules
- H-bonds nees to be broken before state change, requires absorption of energy (heat)
Compare methane to water
- Similar structures, in size & weight
- Comparable valence structures
The function of water’s polarity
polar property attracts other molecules that are polar or have an ionic charge
Cohesion
Ability of like molecules to stick together
Adhesion
ability of dissimilar molecules to stick together
Cohesion of water
strongly cohesive (forms hydrogen bonds)
Adhesion of water
Water will form intermolecular associations with polar and charged molecules
Significance of cohesive properties of water
Explains surface tension
Explain surface tension
H-bonds between water molecules resist low levels of external force (surface tension)
How smaller organisms move across the water surface
high surface tension; sufficiently dense enough to support the creature
Significance of adhesive properties
Explains capillary action
Explain Capillary action
Attraction to charged / polar surfaces allows water to flow in opposition to gravitational forces
Capillary action
Water flowing in opposition of gravitational forces
Purpose of capillary action
Allows water to be transported up plant stems via a transpiration stream
Universal solvent
water; capacity to dissolve large number of subtances
What can water dissolve
substances containing ions (charged particles) or polarity (electronegative atoms)
How water solvency occurs
- Polar attraction of large quantities of water weakens intramolecular forces(ionic bonds)
- –> dissociation of atoms
- Slightly charged regions of water molecules surround atoms of opposing charge
- Dispersive hydration shells form
Substances’ reaction to water
Can be hydrophilic or hydrophobic
Hydrophilic
‘Water Loving’
Freely associate + readily dissolve in water
Hydrophobic
‘Water Hating’
Don’t freely associate / readily dissolve in water
Examples of hydrophobic subtances
Large, non-polar molecules
(e.g. fats, oils,…)
Purpose of water solubility
Transport of essential molecules within the bloodstream depends on water solubility
Transport of molecules in the bloodstream
Water soluble = travel freely in blood plasma
Water insoluble = cannot travel freely
Examples of water-soluble substances
Sodium chloride
Oxygen
Glucose
Amino acids
Examples of water-insoluble substances
Lipids
Proteins
Cholesterol
How lipids move through bloodstream
Non-polar and hydrophobic
Form complexes with proteins (lipoproteins) to move through bloodstreams
