Chemistry Chapter 5: States Of Matter Important Notes

CHEMISTRY IMPORTANT NOTES:

States of Matter:-

Gas Particles:

·       Have no fixed shape or volume.

·       Are far apart, therefore gases can be compressed

·       Are randomly arranged

·       Can move freely from place to place, in all directions

 

Liquid Particles:

·       Take the shape of the container they occupy.

·       Are close together, so liquids have a fixed volume and can only be compressed slightly

·       Are mostly arranged randomly

·       Have limited movement from place to place, in all directions

 

Solid Particles:

·       Have a fixed shape and volume.

·       Are touching each other, so solids cannot be compressed

·       Are usually in a regular arrangement

·       Cannot change positions with each other; they can only vibrate

 

Types of Structure:-

·       Simple molecular or simple atomic

·       Giant ionic

·       Giant metallic

·       Giant molecular

 

Kinetic Theory of Gases:-

·       Gas molecules move rapidly and randomly.

·       The distance between gas molecules is much greater than the diameter of the molecules, so the volume of the molecules is negligible.

·       No intermolecular forces of attraction or repulsion between the molecules.

·       All collisions between particles are elastic; it means that no kinetic energy is lost in collisions.

·       Temperature of the gas is related to the average kinetic energy of the molecules.

 

Ideal gases have 0 particle volume and no intermolecular forces of attraction.

The volume that gas occupies depends on:

·       Its pressure in pascals. (101325 Pa = 1.0 atmosphere pressure)

·       Its temperature in kelvin. (100^oC + 273 = 373 K)

pV = nRT (R is gs constant which is 8.31 J/K mol

 

When we heat a solid:

·       Energy transferred to the solid makes the particles vibrate more vigorously.

·       Forces of attraction between the particles weaken.

·       Solid changes to a liquid at its melting point. (This is melting)

 

When we cool a liquid, the particles:

·       Lose kinetic energy, so they do not move around so readily.

·       Experience increasing forces of attraction.

·       Stop sliding past each other when the temperature is sufficiently low; the liquid solidifies. (This is freezing)

 

When we heat a liquid:

·       Energy transferred to the liquid makes the particles move faster.

·       Forces of attraction between the particles weaken.

·       Particles with most energy are first to escape from the forces holding them together in the liquid.

·       Liquid evaporates; this happens at a temperature below the boiling point.

·       Forces weaken enough for all the particles to become completely free from each other; they move fast and randomly and they spread out.

·       Liquid boils; this happens at the boiling point. (This is vaporisation)

 

When we cool a vapour, the particles:

·       Lose kinetic energy, so the molecules move around less quickly.

·       Experience increasing forces of attraction.

·       Move more slowly and become closer together when the temperature is sufficiently low; the gas liquefies. (This is condensation)

 

Vapour pressure increases, when temperature increases because:

·       Gas particles have more kinetic energy.

·       Gas particles move faster, so they can overcome intermolecular forces of attraction more easily.

 

Properties of Ionic compounds:

·       They are hard; takes lot of energy to scratch the surface because of the strong attractive forces keeping the ions together.

·       They are brittle; it may split apart when hit in the same direction as the layers of ions. Ther repulsions between these ions in the layers, all with same charge, cause the crystals to split along these eleavage planes.

·       High melting points and high boiling points; the attraction between the large numbers of oppositely charged ions in the lattice acts in all directions and bonds them strongly together.

·       Many ionic compounds are soluble in water; they can form ion-dipole bonds.

·       Only conducts electricity when molten or in solution.

 

Properties of Graphite:

·       High melting and boiling points; strong covalent bonding throughout the layers of carbon atoms, so a lot of energy is required to overcome these strong bonds.

·       Very soft, easily scratched; forces between the layers of carbon atoms are weak so the layers of graphite can slide over each other when a force is applied. The layers flake, therefore it is used in pencil ‘leads’ and feels slippery.

·       Good conductor of electricity; when a voltage is applied, the delocalised electrons (mobile electrons) can move along the layers.

 

Properties of Diamond:

·       High melting and boiling points; strong covalent bonding throughout the whole structure, so lot of energy required to break these strong bonds and separate the atoms.

·       Very hard, can’t be scratched easily; difficult to break the three-dimensional network of strong covalent bonds.

·       Doesn’t conduct electricity; no free electrons available to carry the electric current. (4 outer electrons on every carbon atom involved in covalent bonding)

 

Properties of Buckminsterfullerene:

·       Relatively low sublimation point; weak intermolecular forces between each buckminsterfullerene molecule and continuous layered giant structure as in graphite. It turns directly from solid to vapour state when heated to about 600^oC. (Graphite only turns from solid to vapour state at about 3700^oC.)

·       Relatively soft; doesn’t require much energy to overcome the weak intermolecular forces.

·       Poor conductor of electricity compared with graphite; extent of electron delocalisation is lower.

·       Slightly soluble in solvents such as carbon disulfide and methylbenzene. Neither diamond nor graphite is soluble in common solvents.

·       More reactive than graphite or diamond; relatively high electron density in certain parts of the molecule. It reacts with hydrogen, fluorine, chlorine, bromine and oxygen.

Characteristic Properties of Nanotube:

·       High electrical conductivity along the long axis of the cylinder; some of the electrons are delocalised and can move along the cylinder when a voltage is applied.

·       Very high tensile strength when a force is applied along the long axis of the cylinder. (Up to 100 times stronger than steel of the same thickness)

·       Very high melting points (typically 3500^oC); strong covalent bonding throughout the structure.

 

Properties of Graphene:

·       Most chemically reactive form of carbon.

·       Single sheets of graphene burn at very low temperatures and are much more reactive than graphite.

·       Extremely strong for its mass.

·       For a given amount of material, graphene conducts electricity and heat much better than graphite.