Unit 1

• Mole


  A unit of measurement for substances that always contains the same number of particles
• Avogadro Constant (L)


  Allows the number of particles present in a sample of a substance with known mass to be found
• The mole is a very important unit of measurement in many calculations
• Atom


  The smallest part of an element that can exist. All substances are made up of atoms.
• Ion


  What's formed when an atom loses or gains electrons, giving it an overall charge
• Molecule


  Consists of two or more atoms that have been bonded together chemically
• Compound


  A substance that combines two or more different elements through the formation of chemical bonds
• Relative atomic mass (Ar)


  The mean mass of an atom of an element, divided by one twelfth of the mass of an atom of the carbon-12 isotope
• Relative molecular mass (Mr)


  The mean mass of a molecule of a compound, divided by one twelfth of the mass of an atom of the carbon-12 isotope
• The molecular mass (Mr) of a compound or molecule can be calculated by adding together the atomic masses (Ar) of all the atoms in that compound
• Relative formula mass


  Refers to compounds that have a giant structure
• Empirical formula


  The simplest whole number ratio of atoms of each element in a compound, found using molar ratios of each element
• Molecular formula


  The actual number of each atom in the molecule, determined using the Mr of the empirical formula and the true Mr of the molecule
• Molar mass


  The mass in grams per mole of a substance, with units g mol-1
• Parts per million (ppm)


  Concentration given as the mass of a particular species within 1,000,000 total units of mass, commonly used for gas concentrations
• Molar volume of gases


  One mole of any gas at room temperature and pressure takes up the same volume of 24,000 cm3 or 24 dm3
• Ideal gas law


  Describes the relationships between pressure, volume, temperature and moles for gases under standard conditions
• Balanced chemical equation


  Has the same number and type of each atom present on both sides of the equation, with correct reacting ratios
• State symbols


  (s) - solid, (l) - liquid, (g) - gas, (aq) - aqueous (dissolved in water)
• Ionic equation


  Shows just the reacting particles that undergo a change during the reaction, as dissociated ions
• Atom economy


  A measure of efficiency, the proportion of reactant atoms which are converted into the desired product
• Experimental data can be used to work out empirical and molecular formulas and reaction stoichiometries
• Atomic structure model


  Small, dense central nucleus surrounded by orbiting electrons in electron shells
• Nucleus


  • Consists of protons and neutrons
  • Has an overall positive charge
  • Contains almost the entire mass of the atom
• Neutral atom


  Number of electrons is equal to the number of protons due to the relative charges
• Fundamental particles


  • Proton
  • Neutron
  • Electron
• Proton


  Relative charge +1, Relative mass 1
• Neutron


  Relative charge 0, Relative mass 1
• Electron


  Relative charge -1, Relative mass 1/1840
• Maximum number of orbiting electrons in a shell


  2n^2 where n is the number of the shell
• Each electron shell must fill before the next one can hold any electrons
• Mass number (A)


  Sum of protons and neutrons in an atom
• Atomic number (Z)


  Equal to the number of protons in an atom, also known as proton number
• Isotopes are atoms of the same element with the same atomic number but different number of neutrons, resulting in a different mass number
• Neutral atoms of isotopes will react chemically in the same way because their proton number and electron configuration is the same
• Ionic substances


  • Brittle
  • Unable to conduct electricity in solid form
  • Can conduct electricity when molten or aqueous
• The different mass numbers of isotopes means they have different physical properties
• Metals


  • Malleable
  • Conduct electricity when solid
• Relative atomic mass (Ar)


  The mean mass of an atom of an element, relative to one twelfth of the mean mass of an atom of the carbon-12 isotope
• Electron density maps


  • Show the region around a nucleus in which electrons are distributed
  • High density corresponds to high probability of an electron being there