chem

• Elements


  Pure substances that cannot be further broken down
• Compounds


  Pure substances made up of 2 or more elements
• Mixtures

  2 or more substances physically mixed together
• States of matter

  • Solid
  • Liquid
  • Gas
• Changes of state


  1. Increased temperature

  2. S → L → G

  3. Average KE of particles is higher/ move faster
• Atoms


  Composed of protons, neutrons and electrons
• Subatomic particles


  • Proton
  • Neutron
  • Electron
• Protons


  • Used to define elements
• Neutrons


  • Glues the nucleus together + reduces repulsive force of protons
• Electrons


  • Determines chemical properties
• Isotopes


  Atoms that have the same number of protons but different number of neutrons
• Isotopes have different mass, density, melting/boiling point, rate of diffusion but same chemical properties as they have the same number of electrons and same electronic structure
• Mass spectrum

  Used to determine the relative atomic mass of elements
• Calculating relative atomic mass

  Relative Atomic Mass =(mass of each isotope * %abundance)/100
• Continuous spectrum


  Consists of all frequency or wavelength of light, colours merge together
• Emission line spectrum


  Consists of certain frequency or wavelengths of light, when electron drops from an energy level to a lower energy level, it releases energy, colour/wavelength depends on the difference between the two energy levels, only the transitions that correspond to a visible wavelength can be seen on the spectrum, the lines converge because the distance energy decrease the farther away they are from the nucleus
• Absorption spectrum


  Has dark lines in the spectrum, opposite of emission spectrum, when electrons are excited/promoted, they absorb energy/colour from the spectrum
• Energy levels


  Have sub-levels (s, p, d, f) which have different orbital paths, energy levels converge at higher energies (n = 1 → n = 2 is a bigger gap than n=2 →n= 3)
• Sub-levels


  • s
  • p
  • d
  • f
• Orbitals


  • Spaces where a pair of electrons can go, each orbital can hold 2 electrons
• Number of orbitals in each sub-level

  • s* 1
  • p* 3
  • d* 5
  • f* 7
• Aufbau principle


  Electrons fill atomic orbitals of the lowest available energy levels before the higher ones
• Pauli's exclusion principle


  No two electrons can be identical, electrons in the same orbitals have different spins
• Hund's rule


  Electrons entering orbitals that have the same energy must be filled by parallel electrons (unpaired electrons with the same spin) before paired, electrons experience mutual repulsion, therefore need more energy to exist
• Ionization energy


  Minimum energy required to remove 1 electron from 1 mol of gaseous atoms
• As energy increases


  Frequency of electromagnetic radiation increases
• When energy is sufficient to remove an electron from an atom

  Ionization occurs
• Limit of convergence at higher frequencies in emission spectrum

  Corresponds to ionization energy
• Electron in 2p of Boron


  Further away from nucleus than electron in 2s of beryllium, which makes it easier to remove
• Across a period, from B to C to N


  Ionization energy increases as proton number increases, attraction to nucleus increases
• From N to O


  Ionization energy decreases as O has a paired electron in the same 2p orbital, repulsion makes one of them easier to be removed
• Avogadro's constant


  6.02 * 10^23, used to measure large quantities of small atoms/molecules/particles
• 1 mol of any gas at STP = 22.7dm3, equal numbers of moles of any gas occupy the same volume
• Determining relative formula mass

  Multiply the subscript of each element in the formula by its relative atomic mass, then add together
• Empirical formula

  Shows the simplest whole number mol ratio of atoms in each element in a compound/molecule
• Molecular formula


  Shows the actual number of atoms of each element in a compound/molecule
• Molar concentration

  Represented by square brackets, e.g. [NaOH]
• Determining % CaCO3 in limestone

  2g of limestone is put into a beaker and 60cm^3 of 3 mol/dm HCL(in excess) is added, they are left to react and then the impurities are filtered off and the solution is made up to a total volume of 100cm3, of this solution, 25cm3 require 35.5cm^3 of 1 mol dm NaOH for neutralization
• Ideal gas


  Particles are free moving, independently, randomly, move in straight lines until collision, have high kinetic energy
• Assumptions of ideal gas model

  • Particles have negligible volume, all collisions are elastic, intermolecular forces are negligible, KE is proportional to temperature (K)