CHEMISTRY CHANTELLE PAPER 1

• Atoms combine


  Through the movement of electrons to achieve a greater level of stability by obtaining a full outer shell of electrons

  
• Ways atoms can combine

  • Ionic bonds
  • Covalent bonds
  • Metallic bonds
• Ionic bonds

  Take place when metals and non-metals react by transferring electrons, forming oppositely charged particles (ions) held together by electrostatic forces
• Covalent bonds

  Non-metal atoms share pairs of electrons between each other
• Metallic bonds

  Occur in metals and metal alloys, where atoms lose their valence electrons which become delocalised and can move freely between the positive metal ions

  
• Intermolecular forces are not chemical bonds, do not involve electron transfer or sharing, and are around one-tenth the strength of a chemical bond
• Ion

  An electrically charged atom or group of atoms formed by the loss or gain of electrons
• Anion

  Negative ion formed when atoms gain electrons

  
• Cation

  Positive ion formed when atoms lose electrons

  
• All metals lose electrons to become positively charged ions, all non-metals gain electrons to become negatively charged ions
• The number of electrons an atom gains or loses is the same as the charge
• Representing ionic bonds

  • Sodium chloride (NaCl)
  • Magnesium oxide (MgO)

  
• Ionic compounds

  • Consist of a regular arrangement of alternating positive and negative ions in a tight lattice structure, held together by strong electrostatic forces
  • Have high melting and boiling points
  • Form regular solid shapes

  
• Models have limitations in accurately representing ionic compounds
• Covalent bonds

  Form when non-metal atoms share pairs of electrons to obtain a full outer shell

  
• Covalently bonded substances may consist of small molecules or giant molecules, with weak intermolecular forces between individual molecules
• Simple covalent molecules are small and can be separated into individual units without breaking chemical bonds, unlike giant ionic and covalent structures

  
• Polymers and giant covalent structures

  Very large covalently bonded substances like polythene, PVC, graphite, diamond, and silicon dioxide
• Models have limitations in accurately representing covalent bonding and molecular structures
• Metallic bonding

  Occurs in metals and metal alloys, where atoms lose their valence electrons which become delocalised and can move freely between the positive metal ions

  
• States of matter

  • Solid
  • Liquid
  • Gas

  
• Solids


  • Strong forces of attraction between particles, particles packed closely in fixed pattern, atoms vibrate in fixed position
• Liquids


  • Weaker attractive forces between particles, particles close together in irregular form, particles can move and slide past each other
• Gases

  • Particles in random movement, far apart, move quickly in all directions, collide with each other and container walls
• Strength of forces between particles

  Determines energy needed for state changes (melting, boiling, freezing)
• Melting


  Solid changes into liquid, requires heat energy to transform into kinetic energy and allow particle movement
• Boiling

  Liquid changes into gas, requires heat to form gas bubbles and allow liquid particles to escape surface
• Freezing

  Liquid changes into solid, reverse of melting
• Interconversion of state


  A physical change involving changes in the forces between the particles of the substances, the particles themselves remain the same, as do the chemical properties of the substance
• Physical changes are relatively easy to reverse as no new substance is formed during interconversions of state
• Melting


  1. Solid changes into a liquid

  2. Requires heat energy which transforms into kinetic energy, allowing the particles to move

  3. Occurs at a specific temperature known as the melting point which is unique to each pure solid
• Boiling

  1. Liquid changes into a gas

  2. Requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and from within the liquid

  3. Occurs at a specific temperature known as the boiling point which is unique to each pure liquid
• Freezing


  1. Liquid changes into a solid

  2. Reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same

  3. Water freezes and melts at 0 ºC

  4. Occurs at a specific temperature which is unique for each pure substance
• Evaporation

  1. Liquid changes into a gas

  2. Occurs only at the surface of liquids where high energy particles can escape from the liquids surface at low temperatures, below the boiling point of the liquid

  3. The larger the surface area and the warmer the liquid/surface, the more quickly a liquid can evaporate

  4. Evaporation occurs over a range of temperatures, but heating will speed up the process as particles need energy to escape from the surface
• Condensation

  1. Gas changes into a liquid, usually on cooling

  2. When a gas is cooled its particles lose energy and when they bump into each other, they lack energy to bounce away again, instead grouping together to form a liquid
• Sublimation

  1. Solid changes directly into a gas

  2. Happens to only a few solids, such as iodine or solid carbon dioxide

  3. The reverse reaction is called desublimation or deposition
• Particle Theory

  • The amount of energy needed to change from a solid to a liquid and from a liquid to a gas depends on the relative strength of the forces acting between the particles
  • The stronger the forces between the particles, the higher the energy needed for melting and boiling to occur
  • When substances are heated, the particles absorb thermal energy which is converted into kinetic energy
  • Heating a solid causes its particles to vibrate more and as the temperature increases, they vibrate so much that the solid expands until the bonds break and the solid melts
  • On further heating, the now liquid substance expands more and some particles at the surface gain sufficient energy to overcome the intermolecular forces and evaporate
  • When the boiling point is reached, all the particles gain enough energy for the intermolecular forces to break and the molecules to escape as the liquid boils
  • While changing state, the temperature of the substance remains the same as the heat energy goes into breaking the bonds between the particles
  • This is called latent heat
• The entire process can be summarized in a diagram called a heating and cooling curve
• Limitations of the Particle Theory

  • Particle theory considers all particles, irrespective of their state or chemical identity, to be small, solid and inelastic
  • It doesn't consider the difference caused by different particles, such as atoms, ions or molecules or mixtures of all three
  • The theory also fails to consider the intermolecular forces that exist between different particles in different substances
• Predicting Physical State


  1. At temperatures below the melting point, the substance will be in the solid state

  2. At temperatures between the melting point and the boiling point, the substance will be in the liquid state

  3. At temperatures above the boiling point, the substance will be in the gas state