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
• Atoms have a radius of about 0.1 nanometer, and the radius of their nucleus is less than 1/10,000 of the atom
• 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
• To balance a symbol equation, the number of each type of atom must be the same on both sides of the arrow
• Chemical formulas to know

  • Carbon dioxide (CO2)
  • Water (H2O)
  • Oxygen (O2)
  • Hydrogen (H2)
  • Nitrogen (N2)
  • Ammonia (NH3)
  • Hydrochloric acid (HCl)
  • Sulfuric acid (H2SO4)
• Proton


  Positively charged particle found in the nucleus of an atom
• Neutron


  Neutral particle found in the nucleus of an atom
• Electron


  Negatively charged particle found in shells orbiting the nucleus of an atom
• The relative charge of a proton is +1, a neutron is 0, and an electron is -1
• The relative mass of a proton and neutron is 1, while the relative mass of an electron is about 1/2000
• 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 numbers of neutrons
• Ion


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


  • The first shell can hold up to 2 electrons, the 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
• In a neutral atom, the number of protons equals the number of electrons
• Determining particles in an atom/ion

  1. Find the atomic number to get the number of protons

  2. Subtract the atomic number from the mass number to get the number of neutrons

  3. For a neutral atom, the number of electrons equals the number of protons

  4. For an ion, the number of electrons is different from the number of protons by the charge of the 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
• Isotopes


  Have the same number of protons but different numbers 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. / 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