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Expansion on freezing

- Solids are more dense than liquids- Waterexpands when frozen. Ice is less dense?- H bonding highly dependent on orientation- In ice, each water molecule is hydrogen bonded to four other water molecules in a

tetrahedral shape around it.

- Forms a lattice of hexagonal rings -> open cage like structure- As ice melts, water molecules move faster, H bonds are broken and the open rigid

network partially collapses.

- Therefore, water molecules in liquid are closer (higher density!)- Vital to nature- Frozen ice has insulatinglayeron water surface, allowing aquatic animals to live longer

Syllabus ref 3.1.1

a) Soluble ionic compound:- Most ionic compounds soluble in water, polar water molecules are able to pull ions into

solution and then surround then with a hydration sphere.

- The partially negative atom attracts cations (eg. Na+), while the partially negative end (Hbonds) attracts anions (eg. Cl-, D-D attraction)

- Insoluble ionic compounds (eg. AgCl) have ionic bonds that are too strong to beovercome by (????? Sorry I white outed this part; dunno what it is >.

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d) Covalent molecular structure eg. sandSiO glass- Insoluble since the extensive and very strong covalent bond prevents the molecules from

breaking down the structure and dispersing the atoms. Nothing happens.

e) Large molecules (eg. cellulose, polyethene)- Polymer molecules are insoluble in water- So large and extended that water is unable to sufficiently surround them and disperse

them

- Polyethene (polymer of ethane) is large and non polar- Cellulose (polymer of glucose) is polar but forms long linear fibres that can H bond to

one another, preventing water from getting in between the fibres.