Chemistry Paper 1 in 30 mins

• An atom is something that can't be broken down or split into its constituents or smaller bits by chemical means
• A compound is two or more types of atoms chemically bonded together
• A mixture has different types of atoms or compounds not chemically bonded together
• Ways to separate mixtures:

  • Chromatography: water drawn up a filter paper drags particles of the mixture with it, lighter particles end up higher on the paper
  • Filtration: removes insoluble particles like sand from water
  • Distillation: separates a solute from a solvent like salt from water by evaporating the water and recondensing it
• Atoms have a nucleus with neutrons and protons, and electrons orbiting around

  • Protons have a charge of +1, electrons have a charge of -1, neutrons are neutral
  • Atoms have the same number of protons as electrons, making them neutral
  • Atoms become ions by losing or gaining electrons
• Periodic table:

  • 8 main columns, columns/groups indicate the number of electrons in the outer shell
  • Rows/periods indicate the number of electron shells
  • Metals are to the left, nonmetals to the right
  • Group 1: alkali metals, get more reactive going down
  • Group 7: halogens, get less reactive going down
  • Group 8/0: noble gases, very unreactive
• Chemical symbols:

  • Atomic number (bottom) = number of protons
  • Mass number (top) = protons + neutrons
  • Electrons fill shells in a specific order (2, 8, 8, 2 for the first 20 elements)
  • Atoms bond to achieve a full or empty outer shell
• Ionic bonding:

  • Metals donate electrons, forming positive ions
  • Nonmetals accept electrons, forming negative ions
  • Ionic compounds have high melting/boiling points, conduct electricity when molten or dissolved
• Covalent bonding:

  • Nonmetals share electrons to achieve a full outer shell
  • Small molecules form through simple covalent bonding
  • Giant covalent structures like diamond, graphite, graphene, fullerenes, and nanotubes
• Metallic bonding:

  • Atoms form a lattice with delocalized electrons
  • Metals can conduct electricity due to free-moving electrons
• Polymers:

  • Long chains formed by joining monomers
  • Polymerization requires high pressure and a catalyst
• History of the periodic table:

  • Dalton ordered elements by weight
  • Newlands grouped elements with similar properties
  • Mendeleev arranged elements in columns and rows
• Chemical changes:

  • Metals and oxygen form metal oxides (oxidation)
  • Metals and water form metal hydroxides (alkalis) and hydrogen gas
  • Acids and metal hydroxides form salts and water (neutralization)
  • Thermal decomposition breaks down compounds with heat
• Displacement reactions:

  • More reactive metals displace less reactive metals in compounds
  • Used in extracting metals from ores and sacrificial metals
• Rust:

  • Iron reacts with oxygen or water to form iron oxide (rust)
  • Other metals like aluminium and copper can also form oxides
• Quantitative chemistry:

  • Atoms are not created or destroyed in chemical reactions
  • Chemical reactions must be balanced
  • Balanced equations ensure conservation of atoms
• To balance the chemical equation for zinc and hydrochloric acid reacting to form zinc chloride and hydrogen gas:
• Start with the complex molecules and end on the elements
• Put a 2 in front of HCl to balance the chlorines
• If there are more hydrogens on the left, multiply up the H2 on the right
• Relative atomic mass or relative formula mass:
• Calculated from the mass number of an element
• Deals with moles, where a mole is 6.02 x 10^23 atoms or molecules
• Moles = grams / RAM
• RAM tells you how many grams a mole of that substance weighs
• Solution concentration:
• Measured in grams per decimeter cubed or moles per decimeter cubed
• Concentration = grams or moles / volume of the solution
• Percentage yield:
• Compares how much product is obtained from a reaction to the maximum possible
• Calculated as mass of products / maximum theoretical mass
• Moles and gas constant:
• One mole of any gas occupies 24 decimeters cubed of volume
• Volume of a gas = number of moles x 24
• Electrolysis:
• Used to separate chemicals from solutions like brine
• Involves oxidation and reduction at the anode and cathode
• Can be used to purify metals like copper
• Energy changes:
• Exothermic reactions release more energy than needed to break bonds