stpm biology chapter 1 water note

Water

Dipolar molecules

-uneven charge within the molecules

  oxygen (slight -ve charge), hydrogen(slight +ve charge)

-bond angle 104.5°

-hydrogen bond between positively charged oxygen & negatively charge hydrogen in liq. state 

  form, break and reform ( high frequency)

Universal solvent

-caused by polarity of water

• a suitable solvent for ions and polar molecules.
•  displace their attraction to each other.

~polar dissolve in water = hydrophilic 

~nonpolar [lipid and hydrocarbon] = hydrophobic

Density

 In liq. state, water molecules 

• break and reform
• are arranged more irregular but closer

In ice (solid) state, water molecules

• are arranged regularly, hexagonal crystalline lattice
• Each can form a max. no. of  4 hydrogen bond with other water molecules

Advantage of lattice structure of ice

-occupies more space

-has less water molecules per vol.

therefore water expands when it freezes, less dense than liq. water

*Water has max. density at 4°C

-at 0° and below ice floats on surface>>form insulating layer

-prevent water fr. freezing in lower depths

therefore aquatic organisms like fish can survive during winter

 or u can download this one.... BIOLOGY-STPM-LOWER-6-CHAPTER-1