Chemistry Definitions

Periodicity: The occurrence of similar properties in elements occupying similar positions in the periodic table. First ionisation energy: The energy required to remove one mole of the most loosely held valence electron from one mole of gaseous atoms. Electronegativity: The tendency of an atom in a molecule to attract a shared pair of electrons in a covalent bond to itself.

BOND ANGLES:

• Tetrahedral: 109.5
• Trigonal pyramidal: 107
• Bent: 104.5
• Linear: 180
• Triangular planar: 120

Properties of Matter:

• Melting/Boiling point: Temperature is a measure of the average kinetic energy of particles. Melting point is an indicator of the energy required to separate particles into a liquid or gaseous form.

• Hardness: In chemistry, we think of hardness as the relative strength of the chemical bonds within a substance. In other words, it is how resistant a solid is to force applied.

• Density: how compact the particles in a molecule are.

• Electrical conductivity: The ability for a substance to conduct a current of electricity. For a substance to be conductive, it must contain mobile, charged particles.

• Thermal conductivity: The transfer of energy due to molecular motion. For a substance to conduct heat, generally it must have mobile particles to transfer energy.

• Brittle: To be hard, but fracture easily.

Solutions:

- **Solution:** A mixture in which the solute particles are homogenously distributed throughout particles of solvent
      - Can be solid (e.g. Bronze(Metal alloys)), liquid (e.g. Sea water) or gas (e.g. Air)
- **Aqueous Solution:** Liquid solution where the solvent is water
- **Solvent:** The major component of a solution by mass
- **Solute:** The minor components of a solution by mass
- **Dissolving:** Solid particles are separated and distributed throughout the mixture, increasing solution concentration.
- **Unsaturated:** Contains less solute than the solvent is normally able to dissolve
- **Saturated:** Contain the same amount of solute that the solvent is normally able to dissolve
    - Rate of dissolving and crystallisation are equal
- **Supersaturated:** Contains more solute than the solvent is normally able to dissolve
	- Can be achieved through heating and dissolving, then carefully cooling the solution.

Pure substances: A substance that has a fixed composition. This includes elements and compounds.S

Valency: The combining power of an atom, and is equal to the number of hydrogen atoms it could combine with or displace.

Precipitate: An insoluble solid produced by two solutions being added together.

Mole: The amount of particles of a substance that is equal to the number of particles in 12 grams of Carbon-12.

Physical Properties Copy-Paste Moment

• Ionic Bonding:

  • High Melting and Boiling Points
    • Within the ionic lattice, there exists a strong electrostatic attractive force between unlike ions. Thus, a high average kinetic energy of particles is required to separate these ions into the liquid and gaseous phase. As energy is proportional to temperature, this means ionic compounds will have a higher melting/boiling point.
  • Hardness and Brittleness
    • When force is applied to the ionic lattice, layers of alternating ions slide over each other. This causes the distance between like charges to decrease, creating a net repulsive force. This fractures the ionic lattice, making ionic compounds brittle. However, the strong electrostatic attractive force between unlike ions still remains, and requires much more force to break. Thus, ionic substances are hard.
  • Conductivity in Solid, Liquid and Aqueous states
    • For a substance to be conductive, it must contain mobile, charged particles.
    • In the solid state:
      • Ionic solids exist as an lattice of alternating ions.
      • These ions are rigid with regards to the overall structure.
      • As these ions are rigid, they are not mobile despite being charged.
      • Thus, ionic substances are not conductive in the solid phase.
    • In the molten phase:
      • In the molten phase, ions have high kinetic energy and are free to move independently.
      • As ions they are charged (positive or negative).
      • Thus, in the molten phase ionic compounds are very conductive.
    • In the aqueous phase:
      • Ions are attracted to water molecules, which move freely. This means ions are also mobile in an aqueous solution.
      • Ions are also charged.
      • Thus, in the aqueous phase ionic compounds are very conductive.
  • Comparison Question
    • e.g. Element X is a Group 1 element, Element Y is a group 2 element. Which one has the stronger metallic bond?
      • Element Y. As it releases more valence electrons, it becomes more positively charged. Thus, a greater electrostatic force of attraction will exist between Element Y's cations and the sea of delocalised electrons, i.e., the metallic bond. Thus, the metallic bond will be stronger.

• Metallic Bonding:

  • Malleability and Ductility
    • The metallic bond is non-directional, as it is between metal cations and the sea of delocalised electrons.
    • This means when force is applied, cations can move in relation to each other without breaking the metallic bond.
    • Thus, metals can change shape without breaking, and thus are highly malleable and ductile.
  • Thermal and Electrical Conductivity
    • Thermal:
      • To be a thermal conductor, a substance must contain mobile particles to transfer energy via collisions.
      • Within metal solids, there is a sea of delocalised electrons.
      • These electrons are mobile, and thus can carry kinetic(heat) energy.
      • Furthermore, metal cations can vibrate, which further carries kinetic energy.
      • Thus, metals are good thermal conductors.
  • Moderate to High Melting and Boiling Points
    • With a metal solid, there exists a strong electrostatic force of attraction between metal cations and the sea of delocalised electrons. Thus, a high average kinetic energy of particles is required to disrupt the metallic lattice. As energy is proportional to temperature, this means metal solids will have a higher melting/boiling point.

• Covalent Molecular Bonding:

  • Low Melting and Boiling Points
    • For covalent molecular substances, there exists a very strong intramolecular force within molecules, but a weak intermolecular force between molecules. Thus, less energy is required to overcome this weak force and separate molecules. As energy is proportional to temperature, covalent molecular substances have a low melting/boiling point.
  • Non-conductivity
    • For a substance to conduct electricity, it must contain mobile, charged particles. In covalent molecules, electrons remain localised either as within an atom's electron cloud or as part of a shared pair of electrons in a covalent bond. Thus, there are no delocalised electrons, which would be mobile and charged. Furthermore, there are no ions. Thus, there are no mobile charged particles and covalent molecular substances are not electrically conductive.
  • Softness and Brittleness
    • When force is applied to a covalent molecular substance, the weak intermolecular forces are easily overcome, and molecules are separated from each other. This makes covalent molecular substances soft. Furthermore, as this weak intermolecular structure is easily overcome. this makes covalent molecular substances very brittle.

• Covalent Network Bonding:

  • High Melting and Boiling Points
    • Within a covalent network substance, strong covalent bonds exist between all atoms within the structure. For this structure to be disrupted, a large amount of particle kinetic energy is required. As energy is proportional to temperature, covalent network substances will have a very high melting/boiling point.
  • Hardness and Brittleness
    • A lot of force is required to disrupt atoms in a covalent network substance. Thus, these substances are hard and brittle, as applying such a force would fracture the network.
  • Thermal and Electrical Conductivity
    • Thermal:
      • To conduct heat, a substance must contain mobile particles to carry kinetic energy. Electrons are rigid in the covalent network structure, either as part of lone pairs or bonding pairs. The atoms are also held in place. Thus, there are no mobile particles present to carry kinetic energy and thus these substances are thermally non-conductive.
    • Electrical:
      • To conduct electricity, a substance must contain charged particles. Electrons are rigid in the covalent network structure, either as part of lone pairs or bonding pairs. The atoms are also held in place. Thus, there are no mobile charged particles and thus these substances are not electrically conductive. Intermolecular Forces and Solubility:

Backlinks

Recent pages

None found yet.