ch3 - water

what are polar molecules

molecules where the atoms are covalently bonded - share electrons to achieve a full outer shell

why are polar molecules charged

one atom will have a greater share of electrons = partially negative

hence other molecule = partially positive

> this creates positive and negative regions

2 reasons why water classifies as a polar molecule

-2hydrogen and 1oxygen atoms are covalently bonded

-oxygen has greater share of electrons = partially negative

-hydrogen = partially positive

how do hydrogen bonds form between water molecules

from the positive and negative regions interacting

(+ve hydrogen region being attracted to -ve oxygen region of another H2O molecule)

within H2O molecules the atoms are … bonded 

covalently 

between H2O molecules the molecules are … bonded 

hydrogen

what are the 4 key properties of water

-solvent

-transport medium

-coolant

-provides habitat

how does water act as a solvent 

polar molecules e.g. charged solutes Na+ dissolve in water because:

partially +ve charge of H = attracts -ve ions

partially -ve charge of O = attract +ve ions 

> causing each ion to be surrounded and dissolve 

can non polar molecules dissolve in water

no they cant, they are hydrophobic and repel water

what is cytosol and why is it important

liquid found in cells made up of mainly water

enables solutes to dissolve within the cell so can then be transported around:

animals blood OR plants xylem to cells which need it

what is cohesion

water molecules sticking together due to hydrogen bonds

what is adhesion

water bonding with other molecules like cellulose in the cell wall

how does water act as a transport medium

cohesion enables water molecules to move up the xylem in a continuous column & adhesion enables water molecules to stick to cellulose

when water evaporates why does it to move up easily 

the fact that water molecules are cohesed together means they are pulled up in a continuous column 

what does specific heat capacity mean

energy required to raise 1kg of a substance by 1C

what does latent heat of vaporisation mean

energy required to change a substance from a liquid to a gas

how does water act as a coolant and why is it an advantage - SHC

water has high SHC due to lots of energy being required to break hydrogen bonds between water molecules 

adv: reduces temp fluctuations - which causes ice caps to melt, sea levels to rise destroying habitats

reduces enzymes likelihood of denaturing

how does water act as a coolant and why is it an advantage - LHV

water has high LHV due to lots of energy being required to break hydrogen bonds between water molecules to turn it into a gas

adv: creates cooling effect when animals sweat or plants transpire

what does density mean

how much mass an object has per unit volume

2 ways in which water provides habitat

> cohesion creates surface tension allowing small invertebrates to move and live on water 

> ice is less dense than water so ice floats on water allowing larger animals to move and live on ice 

why is ice less dense than water

when water freezes more Hydrogen bonds are formed which spreads H2O molecules apart, decreasing density