Basics

• Separation techniques


  Use differences in the materials physical and chemical properties in order to separate them, this includes particle size, density, boiling point, and electric charge
• Sieving


  Separate mixtures of solids based on particle size
• Filtration


  Separate mixtures of solids and liquids based on particle size
• Sedimentation and decantation


  Separate mixtures of solids and liquids based on density
• Separation funnel


  Separate mixtures of immiscible liquids of different densities
• Centrifugation


  Separate mixtures of components where the differences in density are very small
• Evaporation


  Separate the solute from the solvent in solutions but the solvent is not retained
• Distillation


  Separate the solute from the solvent in solutions, or even two miscible liquids, and all components are retained
• Fractional distillation


  Separate mixtures of miscible liquids with similar boiling point
• Electrostatic separation


  Separate a mixture of substances that respond differently to external electric
• Separation techniques


  • Separation by electric charge: electrostatic separation, chromatography
  • Separation by density: sedimentation and decantation, separation funnels, centrifugation
  • Separation by boiling point: evaporation, distillation
  • Separation by particle size: sieving, filtration
• Gravitational filtration


  Uses weight of solid-liquid mixture through filter paper, pour solid-liquid mixture into filter paper and left to run through the funnel, filtrate is purified liquid that collects in the flask, residue is the solid collected in the filter paper
• Vacuum filtration


  Faster than gravitational filtration, also helps dry residue more quickly, solid-liquid mixture poured into the funnel is sucked into the flask by the vacuum the solid residue is trapped by filter paper
• All substances are made from atoms
• Atom


  Composed of small positively charged nucleus surrounded by negatively charged cloud of electrons, nucleus made of two subatomic particles called nucleons: neutrons, protons, protons and neutrons are similar in size but electrons is x1800 smaller, charges on protons and electrons are equal but opposite resulting in the atom to be neutral charge as neutrons have no charge
• Atomic number


  The number of protons in the nucleus of an atom
• Mass number


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


  Atoms of the same element that have the same atomic number but different mass numbers, they have the same number of protons but different numbers of neutrons
• Isotopes


  • They have the same chemical properties but different physical properties
  • Isotopes with a significantly different number of neutrons to protons tend to be unstable and therefore radioactive
  • Radioactive isotopes undergo radioactive decay , emitting various forms of radiation to become lighter, more stable nuclei
• Relative atomic mass


  The weighted average of the relative isotopic masses taking account their relative abundance in nature
• Mass spectrometry


  Separates the individual isotope in a sample of the element, determines the mass of each isotopes, relative to the carbon-12 standard, calculates the relative abundances of the isotope in the sample
• Mass spectrum


  A plot of measured abundances of each isotope against the mass-to-charge ratio (m/z), the number of peaks indicates number of isotopes, the position of the peaks on the horizontal axis indicates relative atomic mass, the relative heights of the peaks corresponds to the relative abundance of isotopes
• Bohr model


  • Electrons revolve around nucleus in fixed circular orbits, the electrons orbits corresponds to specific energy levels or shells in the atom, electrons can only occupy these fixed energy levels and cannot exist between two energy levels, electron orbits of larger radii correspond to energy levels of higher energy
• Electron shell


  The region of space the electron occupies, electron orbits nucleus at fixed distance from nucleus
• Energy level


  Shell corresponds with fixed quantity of energy and a by electrons occupying that shell possess the same quantity energy
• It is possible for electrons to move between energy levels by absorbing or emitting energy in the form of light
• Valence electrons


  Electrons in the outermost shell, require least amount of energy to be removed from atom and they are involved in chemical reactions
• Octet rule


  Atoms lose, gain or share valence electrons in order to achieve 8 electrons in outermost shell when they are involved in chemical reactions
• Early periodic table


  • Elements were placed in order of increasing mass of the atoms, arranged elements with similar properties in vertical columns, proposed periodic law: the properties of elements vary periodically with their atomic weights
• Atomic number


  What makes one element different from another element, elements are arranged in rows in order of increasing atomic number
• Modern periodic table


  • Arranged in order of increasing atomic mass, atomic number located above chemical symbol, relative atomic mass located under chemical symbol, horizontal rows known as periods labelled 1-7, vertical columns known as groups labelled 1-18, main group elements are elements in group 1,2 and 13-18, elements in group 3-12 are transition metals
• Electron configuration


  The number of electrons in each shell separated by commas, starting at the shell with lowest energy (closest to nucleus), a max of 2 in the first shell, 8 in the second and 8 in the third shell
• Ion


  A charged particle, happens when number of protons does not equal number of electrons, anions when atom obtains additional electrons, cations when atom loses electrons
• Group number


  For main group elements, can be used to determine the number of valence electrons in an atom of the element, in groups 1 and 2 the number of valence electrons is equal to the group number, in groups 13-18 the number of valence electrons is equal to group number minus 10, helium is exception as it has two valence electrons and is in group 18
• Groups


  • Elements in the same group have the same number of valence electrons, so they have similar chemical properties e.g. alkali metals group 1, halogens group 17, noble gases group 18
• Period


  Numbered 1-7, the period is equal to the number of occupied electron shells in elements atom, provide information about an elements electron configuration, summarising relative properties of elements and explaining the trends observed in those properties
• Electrostatic attraction


  The force that holds individual atoms together, holds atoms together in molecules and then holds molecules together in all forms of matter, strength is directly proportional to magnitude of charges involved and inversely proportional to the distance between charges squared
• First ionisation energy


  The energy required to remove one electron from an atom of an element in the gas phase, reflects how strongly the valence electron is attracted to nucleus of atom
• Successive ionisation energy


  The energy required to achieve the sequential removal of electrons from the atom, increases as more tightly held inner shell electrons are removed
• Core charge


  A measure of the attractive force felt by the valence electrons towards the nucleus, calculated as number of protons - number of total inner-shell electrons