CATEGORY ： Chemistry 12 Bonding 02 2007/02/18 Sun TB ： CM ： 0 △

Relative Strengh of Bonds

the 1st - Network Crystal the 2nd - Metallic
the 3rd - Ionic
the 4th - Covalent
the 5th - Hydrogen Bonding
the 6th - Dipolar Forces
the 7th - London Forces
(orderd by strangest to weakest)

This a generalization which can be used to place substances in order of Melting points. The higher the melting point, the stronger the bond.



1. Network Crystals

- very high melting points.
- covalently bonded into marro molecules
- contains metalloids but C and Si are most common.
- Carbon is bonded itself as diamond or Graphite
- very hard, stable, non conducters (except graphite "layers")

GEN: If it contains Si or C(by itself) it is network crystal.

m.p. SiC₂-2,700℃, C_pia-3500℃



2. Metalic

- Wide range (-39~3,400℃)
- Group 1 and 12 are low
- W-Tungsten is highest
- Ase of delocalized electrons
- Conducts heat, electricity
- Left side of dercodict
- Alloys-Metals with
IMPURITIGS ADDED- Greatly
INCREASES melting points
m.p. OS-2700℃, Ni-1455℃, Li-181℃



3. Ionic

NaCl - m.p. 801℃
NaF - m.p. 988℃

- Not molecules, regular sharped crystals
- Molten compounds conduct
- Dissolve in water to form IONS, and CONDUCT ELEC
- Higher electronegativity diff. Has hiher melting point
- polyatomic ionic compounds are usually weaker
NaF - 988℃, NaI - 651℃, NaOH - 318℃



4. Covalent

- Not involved in melting or boiling points



5. Hydrogen Bonding

- Most contain Hydrogen Bonded to fivorine nitrogen or oxygen
- Very important in biological systems



6. Dipolar Forces

Parmanent Dipole
Hcl m.p. -112℃

GEN: The greater the molar mass(size) the greater the melting point.
HI m.p. -50℃, HBr m.p. -88℃, HCr m.p. -112℃



7. London (dispersion forces)

He m.p. -277℃ 1k, Ne m.p. -248℃ 25k

These weak forces are due to temporary induced dipoles

Electrons are further amay from the nucleus, it is easier to induce a dipole, therefore it usually has a higher m.p.


Non polar molecules like CH₄, C₂₅H₅₂, CCl₄ Are usually placed aith London Forces



If they have a large molar mass, their attractions are strang enogh to became solids at room temperature.
CH₄ m.p. -183℃, C₆H₁₂ m.p. 6.6℃, C₁₈H₃₈ m.p. 28.2℃,

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All substances dissolve in water to a certain extent

Soluble
- HIGH - Na, Cl, Alcohol
- LOW - Ba, CO₃, Mg(OH)₂

Nonsoluble - Way Oil

Insoluble is an order term for "very low(nonsoluble)"



Why does NaCl Dissolve in water?

- "Like dissolves like"
- "Polar dissolves Polar"

Hydration: Surrounding by water molecules



Why does carbon tetrachloride not dissolve in water?

- "Water molecules want to stick together"




Why does CCl₄ dissolve in CS₂?>BR?
- "Non polar in Non polar"

It is very easy to break London Forces. The linetic energy (motion) of the Molecules is enough to cause dissolving



How can I speed up dissolving? Heat, stirring
How can I get more to dissolve? Heat