Chemistry Paper 1

• An atom is the smallest part of an element that can exist
• Chemical symbol


  Represents atoms of an element, always starts with a capital letter and consists of one or two letters
• Atom


  • Radius of about 0.1 nanometer (1 * 10^-10 m)
  • Radius of nucleus is less than 1/10,000 of the atom radius (about 1 * 10^-14 m)
• Element


  A substance made up of only one type of atom
• Compound


  A substance which contains two or more different elements which are chemically combined in fixed proportions
• Compounds


  Have different properties from the elements that made them
• Compounds can only be separated into elements by chemical reactions, not physical processes
• Chemical reaction


  1. Formation of one or more new substances

  2. Often involves an energy change
• Word equation


  Represents a chemical reaction using the names of the substances
• Symbol equation


  Represents a chemical reaction using the chemical formulas of the substances
• Balancing a symbol equation

  Ensure the same number of each type of atom on each side of the arrow
• Chemical formulas to know

  • CO2 (carbon dioxide)
  • H2O (water)
  • O2 (oxygen)
  • H2 (hydrogen)
  • N2 (nitrogen)
  • NH3 (ammonia)
  • HCl (hydrochloric acid)
  • H2SO4 (sulfuric acid)
• Atom


  • Made up of protons (positively charged), neutrons (no charge), and electrons (negatively charged)
  • Protons and neutrons in the nucleus, electrons in shells orbiting the nucleus
• Atoms of different elements have different numbers of protons
• Atoms of the same element have the same number of protons
• Isotopes


  Atoms of the same element with the same number of protons but different number of neutrons
• Ion


  A charged particle formed when an atom or molecule gains or loses electrons
• Electron shells


  • First shell can hold up to 2 electrons
  • Second and third shells can hold up to 8 electrons each
• Mass number


  The sum of the number of protons and neutrons in an atom
• Atomic number


  The number of protons in an atom
• Determining number of protons, neutrons, and electrons in an atom or ion

  1. Use the mass number and atomic number

  2. Number of protons = atomic number

  3. Number of neutrons = mass number - atomic number

  4. Number of electrons = number of protons (for a neutral atom), or number of protons plus/minus the charge (for an ion)
• Relative atomic mass


  The average mass of all the atoms of an element compared to 1/12 the mass of a carbon-12 atom
• The relative atomic mass of some elements on the periodic table are not whole numbers
• Mass number


  Protons plus neutrons
• Calculating neutrons


  80 minus number of protons
• Electrons in an ion


  One more than the protons
• Relative atomic mass


  The average mass of all the atoms of an element when compared to 1/12 the mass of a carbon-12 atom
• Relative atomic mass of some elements on the periodic table are not whole numbers
• Relative atomic mass is an average of several different isotopes
• Isotopes


  Same number of protons but different number of neutrons
• Calculating relative atomic mass


  Percentage of isotope 1 x mass of isotope 1 + percentage of isotope 2 x mass of isotope 2, etc. Divide by 100
• Mixture


  Two or more elements or compounds which are not chemically combined
• Methods to separate mixtures

  • Filtration
  • Crystallization
  • Simple distillation
  • Fractional distillation
  • Chromatography
• Filtration


  Pour mixture through filter paper, insoluble solid stays in filter paper, liquid passes through
• Simple distillation


  Heat solution, vapor condenses in condenser
• Fractional distillation


  Heat mixture, vapors with lowest boiling point evaporate first and condense separately
• Crystallization


  Gently heat mixture, evaporate solvent, leave to cool and crystallize, filter and dry
• Chromatography


  Spot mixture on paper, solvent carries components at different rates, separate into spots
• Development of atomic model

  • Dalton's model
  • Plum pudding model
  • Nuclear model
  • Electron shell model
  • Discovery of protons and neutrons
• Periodic table


  Arrangement of elements with similar properties occurring at regular intervals