elements of life

• absorption spectrum: a coloured spectrum with dark bands on it that represent where electrons have absorbed energy
• emission spectrum: a dark background with bands of colour representing where electrons are emitting energy
• absorption: when a beam of light hits an electron, it is given extra energy and so will jump energy shells up from a ground state (lower energy) to an excited state (higher energy)

  only if absorbed the exact amount of energy needed to jump shellls
• emission: when an excited electron drops back down to its ground state, it releases a photon of light (in a particular colour)
• particles absorb / emit light via electrons

  electrons will absorb / emit discrete packets of energy (photon) to jump between the different energy levels

  the quantum energy needed relates to a specific frequency of light --> different elements emit different frequency lights
• uses of emission and absorption spectrum:

  • to identify elements (emission spectrum)
  • to determine the electron energy levels of atoms
• Li+ flame colour = crimson
• Na+ flame colour = yellow
• K+ flame colour = lilac
• Ca2+ flame colour = orange-red
• Ba2+ flame colour = orange
• Cu2+ flame colour = green - blue
• theories of light:

  • wave theory
  • particle theory
• wave theory : light can be described by its wavelength and frequency

  speed of light = wavelength x frequency
• particle theory : light can be described as tiny packets of energy called photons

  quantum energy of photon = planck's constant x frequency of radiation
• electromagnetic spectrum in increasing frequency and decreasing wavelength

  • infrared
  • visible
  • ultraviolet
• • larger nuclei are made by combining smaller nuclei
  • requires huge amounts of heat and pressure
  • highly exothermic
  • once nuclei equal to or more than the nucleus of iron are made, more energy is retained in the resulting nuclei, so the reaction is endothermic
• isotopes: atoms of the same element with a different number of neutrons (same number of protons)
• relative atomic mass of an element: the average mass of its atoms
• % abundance calculations

  (% of isotope x isotope value) + (% of isotope x isotope value)

  -------------------------------------------------------

  100
• periodicity: the repeating patterns elements show across the different periods, relating to physical and chemical properties of the elements
• periodicity in nuclear charge

  • atoms in the periodic table are arranged in order of increasing atomic number
  • each subsequent atom has an extra electron and an extra proton across a period
  • this results in an increasing nuclear charge (more positive) across a period and down groups
• periodicity in bonding and structure

  • across a period, bonding changes from metallic to covalent and structures go from giant lattice to simple molecules
  • down a group, bonding type remains more or less the same
• electronegativity: the measure of the pull of an atom of an element on the electrons in a chemical bond

  stronger pull power = higher electronegativity
• periodicity in electronegativity

  • electronegative elements can result in polar compounds being formed
  • electronegativity is low on the left sid of the periodic table and increases towards the right as nuclear charge increases
  • electronegativity decrease down the group as the nuclear charge increases
• polar compounds: where electrons are not shared evenly (partial charges present)
• atomic number: number of protons
• mass number: sum of protons and neutrons
• isotope: atoms of the same element with the same number of protons but a different number of neutrons, i.e. a different mass number
• number of particles = moles x avogadro's constant
• moles: a way of measuring the amount of a substance
• mass = n x Mr
• moles = concentration x volume
• volume = moles x 24dm
• empirical formula: the simplest whole number ratio of elements in a compounnd
• empirical formula process

  1. write out elements involved
  2. write out %s as masses
  3. divide mass by Mr to get number of moles
  4. divide all by smallest number of moles
  5. times all by two if any end in .5
• to work out molecular formula using empirical formula

  • work out Mr of empirical formula then divide by Mr of molecular formula, use this number to multiple all the atoms in the empirical formula
• % yield = (actual yield / theoretical yield) x 100
• water of crystallisation can be worked out by recording the mass of product, then heating to remove water, reweighing, and then recording again
• titrations use: to work out the concentration of an acid or alkali