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2019.10.16

Chemistry

Reasons of Physical Properties

 

Structure and properties

 

Physical properties: can be detected or measured by sensory organs or testers

  • State
  • Melting point
  • Boiling point
  • Density
  • Hardness
  • Viscosity
  • Solubility

Physical properties depend on:

  • Features of particles (polar on nonpolar)
  • Interactions between particles (intermolecular forces)

Examples:

  • Viscosity of oils and water
  • State of halogens
  • High boiling point of water
  • Relative density of gases
  • Solubility of gasoline in water

 

Crystal lattice

 

Solid substances:

  • strong interaction
  • particles are shaking in fixed position

Crystal:

  • well-ordered particles (salt, metals, sugar, quartz)
  • melting point

Amorphous substances:

  • no order (fat, honey, wax, glass)
  • get softer when heated

 

 

Lattice types

Atomic lattice

Ionic lattice

Metallic lattice

Molecular lattice

Particles

Atoms

Ions

Metal ions and delocalised electrons

Molecules (or noble gas atoms)

Type of attraction

Covalent bonding

Ionic bonding

Metallic bonding

Intermolecular forces (Van der Waals, dipol-dipol, Hydrogen bonding)

Strength of attraction

Strong

Strong

Strong (usually)

Weak

Hardness

Hard

Hard

Hard (usually)

Soft

Melting point

High

High

High (usually)

Low

Can conduct electricity?

No (insulator)

No (insulator)

Yes (conductor)

No (insulator)

Can conduct heat?

No (insulator)

No (insulator)

Yes (conductor)

No (insulator)

Solubility

Insoluble

In polar solvents

Physically no (some react with water, e. g. Na)

In polar or nonpolar solvents

Types, examples, specialities

Diamond, quartz

Salts (NaCl, KF)

metals (Fe, Cr, Al, Ag, Cu, Ag, Zn, Mg)

H2O, HCl, I2

 

 

Structure and solubility

 

Water:

  • dissolves ionic or dipole substances and molecules forming hydrogen bonds
  • hydration: forming hydration shell of water molecules surrounding the dissolved particle
  • cannot dissolve nonpolar substances (fats, oils, gasoline)

 

 

 

Diffusion, dissolution, osmosis

 

Gases, liquids: particles are moving

Diffusion: particles of substances spread evenly in space

Dissolution:

  • mixing of solute and solvent particles
  • interaction between solvent and solute particles (in water: hydration)

Osmosis:

  • semipermeable membrane blocks the diffusion of larger particles
  • water can move, other substances not

 

 

Solubility

  • maximum mass of solute dissolved in100 g of solvent (at a fixed temperature)

Depends on:

  • quality of the substance
  • temperature
  • pressure (in case of gases)

Saturated solution cannot dissolve more solute (unsaturated: can)

Rate of dissolution

  • amount of dissolved substance/unit of time
  • can be increased by stirring up (diffusion), grinding (surface area)