chemistry paper 1 triple

• Dalton's model of the atom

  A cloud of positive charge, with negative electrons embedded in it. Protons and neutrons had not yet been discovered
• Plum pudding model


  Positive charge distributed throughout the atom, with negative electrons embedded in it
• Alpha scattering experiment


  1. Scientists fired alpha particles at a piece of gold foil

  2. They expected the alpha particles to travel straight through the gold

  3. They were surprised that some of the alpha particles bounced back and many were deflected
• Nuclear model


  Scientists replaced the plum pudding model with the nuclear model and suggested that the positive charge and mass of an atom must be concentrated in a very small space at its centre, called the nucleus
• Atom


  • Radius of 1x10^-10m
  • Nucleus (plural nuclei) are around 20,000 times smaller than atoms and have a radius of around 1x10^-14m
• Bohr model


  Electrons must orbit the nucleus at fixed distances, called shells or energy levels
• Relative mass


  Protons and neutrons have the same mass, so are given a relative mass of 1. It takes almost 2000 electrons to equal the mass of a single proton, their relative mass is so small that we can consider it as 0
• Proton


  Particle with an opposite charge to an electron, found in the nucleus
• Neutron


  Particle with no charge, found in the nucleus
• Atoms have equal numbers of protons and electrons, making them have no overall charge</b>
• Atoms of the same element can have a different number of neutrons, giving them a different overall mass number</b>
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Relative atomic mass


  The average mass of all the atoms of an element, taking into account the abundance (percentage of atoms with a certain mass) of each isotope
• Mixture


  Two or more elements or compounds that are not chemically combined together
• Separating mixtures


  Filtration, crystallisation, simple distillation, fractional distillation, paper chromatography
• Covalent bond


  When electrons are shared between non-metal atoms to form a strong chemical bond
• Covalent structures


  • High melting and boiling points because the covalent bonds must be broken
  • Solid at room temperature because the covalent bonds hold the atoms together in a rigid structure
  • Do not conduct electricity because there are no free electrons or ions to carry charge
• Graphite


  A giant covalent structure made of layers of carbon atoms, with delocalised electrons that can carry an electric current
• Graphene


  A single layer of graphite, with strong covalent bonds and the ability to conduct electricity
• Fullerenes


  Hollow cages of carbon atoms arranged as spheres or tubes, held together by weak intermolecular forces
• Ion


  An atom that has gained or lost electrons, giving it a positive or negative charge
• Ionic bonding


  When metal atoms transfer electrons to non-metal atoms, forming positive and negative ions that are attracted to each other
• Ionic structure


  • Giant ionic lattice of positive and negative ions held together by strong electrostatic forces
  • High melting and boiling points because the electrostatic forces are strong and require a lot of energy to break
  • Solid ionic substances do not conduct electricity, but molten or dissolved ionic substances do conduct because the ions are free to move
• Metallic bonding


  Metal atoms lose their outer electrons to form a 'sea' of delocalised electrons, which are attracted to the positive metal ions
• Metallic structure


  • Layers of positive metal ions with delocalised electrons in between, allowing the layers to slide over each other (making metals malleable)
  • Good conductors of electricity and thermal energy because the delocalised electrons are free to move
  • High melting and boiling points because the electrostatic forces between the metal ions and delocalised electrons are strong
• Alloy


  A mixture of a metal with one or more other elements, which can make the resulting material harder than the pure metal
• Metallic structure


  The structure that makes for layers. The electrons in the outer shells are free to move
• Metallic bonding


  The positive metal ions are attracted to the delocalised electrons by the electrostatic force of attraction
• Metals


  • Malleable because the layers can slide over each other
  • Good conductors of electricity and thermal energy because delocalised electrons are free to move through the whole structure
  • Have high melting and boiling points because the electrostatic force of attraction between metallic ions and delocalised electrons is strong, so lots of energy is needed to break it
• Alloy


  A harder mixture made by adding atoms of a different element to a pure metal, which disturbs the regular arrangement of the layers and prevents them from sliding over each other
• The first periodic table, Mendeleev's Periodic Table, and the modern Periodic Table have a number of differences in how they organise elements
• Group 1 elements are very reactive and form positive ions by losing one electron
• Reactivity increases down Group 1 because the atoms get larger, the outer electron is further from the nucleus, and there are more electron shells shielding the outer electron
• Group 7 elements are called the halogens and are non-metals that exist as molecules made up of pairs of atoms
• Reactivity decreases down Group 7 because the atoms get larger, the outer shell is further from the nucleus, and there are more electron shells shielding the outer shell
• More reactive Group 7 elements can displace less reactive ones from a compound
• Transition metals


  • Can form many different charged ions
  • Often act as catalysts to increase the rate of a reaction without being used up
  • Form coloured compounds
• Nanoparticles


  Particles with dimensions in the range of 1-100 nanometres, which often have very different properties to the bulk material due to their high surface area-to-volume ratio
• Nanoparticles have many uses, such as in healthcare, electronics, and as catalysts, but also have potential hazards that require further research
• In a chemical reaction, the total mass of the reactants must equal the total mass of the products due to the conservation of mass