topic 1

• the atomic theory suggests that all matter is composed of atoms. All matter is made up of three sub-atomic particles, protons, neutrons and electrons
• electrons have a -1 charge and exist in shells/energy levels constantly moving around the nucleus. They are held by the electrostatic force of attraction between positive nucleus and negative electrons
• atomic number = number of protons =number of electrons
• mass number = number of protons + number of neutrons
• ions are atoms with a charge due to losing/gaining an electron
• period number = number of shells. corresponds to the location of the outermost electron
• group number = number of valence electrons is the last period
• ground state = electrons orbit around the positively charged nucleus in defined energy levels as described by their electron configuration.
• heat energy (flame) causes electrons to absorb energy and jump to energy levels further from nucleus (higher energy). The electron is unstable and immediately falls back to the ground state. Absorbed energy is released in the form of light
• emission spectra: amount of energy released/emitted

  • after being in "excited state", electrons become unstable and must return to lower energy levels
  • as it falls back into ground state, it emits excess energy in the form of visible light that corresponds to the difference in energy between higher/lower levels.
• Atomic absorption spectroscopy detects the metal ion concentration in solutions by comparing the sample to a series of diluted standard solutions to determine concentrations (quantitative)
• flame tests are based on the ability of electrons to emit/release absorbed energy as they move from higher to lower energy levels.
• flame tests detect the metal ion concentration in a sample.

  • Under heat, metals produce different colours based on energy levels (different distances from nucleus)
  • wavelength unique to the element.
  • Only some metals are detectable, as wavelength of light may not be on visible spectrum (qualitative)
• • solution sprayed onto flame (vapourisation)
  • light source emits light of wavelength required to excite electrons
  • atomic vapour in flame
  • light beam passes through filter (hollow cathode lamp) and intensity is measured by electronic detector
  • calibration curve produced

  
• isotopes have same number of protons, different number of neutrons. Same atomic number, different mass number.
• • Isotopes have the same number of valence electrons so same chemical properties. (same electron configurations)
  • Different physical properties due to different masses (different number of neutrons)
• the absorption spectra:

  • electrons in shells closer to nucleus have lower energies and experience a strong attraction to the nucleus
  • an electron can "jump" shells if it absorbs enough energy that corresponds to the energy difference between shells, electron becomes "excited"
  • energy required to promote ground state electrons are supplied by electromagnetic radiation of varying wavelengths/frequencies displayed by unique colours
• mass spectrometer determines accurate masses and abundances of isotopes of an element in a particular sample
• 1. ionisation: after sample is vapourised it is bombarded with a stream of high energy electrons which then produce positive ions by "knocking" electrons off atoms
  2. acceleration: positive ions are accelerated/sped up by electric field
  3. deflection: positive ions are deflected by magnetic field. Lower mass, higher deflection. Charge at +1 so deflection depends on mass
  4. detection: mass to charge ratio measured and relative amounts for each ion, used to calculate AR, mass spectrum produce.
• Relative Atomic mass AR = sum of (% abundance x atomic weight per isotope or relative atomic mass)/ sum of abundances (100 if %)
• across a period:

  • nuclear charge increases due to additional proton
  • no. of shells stays the same = shielding effect by inner electrons stay the same
  • greater core charge acting over same distance
  • valence electrons more strongly attracted to nucleus

  more energy required to remove an electron, 1st ionisation increases

  size of atom decreases, smaller atomic radius

  easier to attract incoming electron, increasing electronegativity
• down a group:

  • no. of shells increase, shielding effect by inner electrons increases
  • core charge stays the same but must act over a greater distance
  • valence electrons less strongly attracted to nucleus

  less energy required to remove an electron, 1st ionisation decreases

  size of atom increases, larger atomic radius

  more difficult to attract an incoming electron, electronegativity decreases
• 1st ionisation energy is the amount of energy required to remove the first electron in the outermost shell from an atom in the gaseous phase

  i.e. C(g) --> C(g)+ + e- 1st
• there is an increase in successive ionisation energies because each electron is being removed from an ion with a progressively larger positive charge
• big jump = changing of shells, large increase of energy, more energy required to remove inner shell electrons because they are more strongly attracted to nucleus
• electronegativity is the attraction atoms have for the shared electrons within covalent bonds
• valency is the charge of anion and number of covalent bonds
• matter is made up of pure substances or mixtures
• homogenous is uniform in composition and properties throughout i.e. pure substances
• pure substances are:

  • constant chemical composition
  • elements/compounds
  • homogenous
  • cannot be PHYSICALLY separated into simpler substances - can be chemically separated
  • have unique physical and chemical properties
• heterogenous: non uniform composition and properties throughout
• mixtures:

  • can be separated by physical means
  • display a combination of chemical and physical properties
  • can have varying composition
• homogenous mixtures are solutions, can be solid, liquid or gaseous.

  • gaseous: air (nitrogen, oxygen, etc.)
  • solid: brass (copper and zinc)
  • liquid: fizzy drinks (carbon dioxide in water)
• physical change is a change in substance which does not result in a new substance being produced. Includes change in state i.e. when water heated = steam
• chemical change is a change in which a new substance is formed (chemical reaction) i.e. electricity in water
• physical properties can be determined without changing chemical composition. i.e. observed
• chemical properties describe changes that occur when a substance decomposes/reacts with other substances to form a new substance
• decantation: separation by density. Solid-liquid

  
• chromatography: separation by solubility. Solvent water (mobile phase) will move up through paper (stationary). different components will separate out based on how well they have dissolved

  
• centrifugation: separation by mass. Sample is spun and separated by. must be perfectly weighted. Denser particles pushed to outside of container by centrifugal force