atomic structure

• the periodic table


  lists all chemical elements, with eight main groups each containing elements with similar chemical properties
• compounds 


  contain more than one type of atom
• atom


  tiny particles that all substances are made up of

  has a tiny nucleus at its centre, surrounded by nucleus
• reactants


  the substances you start with
• products 


  the new substances made
• law of conservation of mass


  the total mass of the products formed in a reaction is equal to the total mass of the reactants
• balanced equations 


  must be the same number of each type of atom on each side of a symbol equation
• state symbols


  (s) - solid

  (l) - liquid

  (g) - gas

  (aq) - aqueous solutions
• compounds

  • have a fixed composition
  • chemical reactions must be used to separate the elements in a compound
  • there are chemical bonds between atoms of the different elements in the compound
  • contain more than one type of atom
• mixtures

  • no fixed composition
  • can be easily separated
  • there are no chemical bonds between atoms
• ways to separate mixtures

  • filtration
  • crystallisation
  • distillation
  • chromatography
• filtration


  used to separate substances that are insoluble in a particular solvent from those that are soluble in the solvent

  e.g - sand, salt and water (the sand is insoluble)
• distillation


  collecting the solvent (instead of letting it evaporate) while separating the soluble solid

  e.g - obtaining pure water from salt solution
• crystallisation


  heating a solution in an evaporating dish on a water bath

  e.g - obtaining sodium chloride from its solution in water
• fractional distillation 


  an effective way of separating miscible (mixable) liquids using a fractionating column. the separation is possible because of the different boiling points of the liquids in the mixture
• paper chromatography


  separates mixtures of substances dissolved in a solvent as they move up a piece of chromatography paper. the different substances are separated because of their different solubilities in the solvent used.
• evidence of electrons


  at the end of 1800s, JJ Thompson discovered the electron
• the first

  • the ancient greeks were the first to have ideas about particles and atoms
• john dalton

  • put his idea forward about atoms in 1800s, he believed they were tiny, hard spheres. he also suggested that each chemical element had its own atoms that differed from others in their mass. believed that they couldn't be divided, that atoms were the fundamental building blocks of nature
• dkiks sk
• geiger and marsden


  the alpha particle scattering experiment carried out by them changed the plum pudding theory. it was proposed that the electrons must be orbiting around the nucleus which contain very dense positively charged protons.
• niels bohr


  in 1914, this man revised the atomic model and suggested that the electrons must be orbiting the nucleus at set distances, in certain fixed energy levels. the energy must be given out when excited electrons fall from a high to a low energy level.
• neutrons discovery

  scientists speculated that there were 2 types of sub atomic particles inside the nucleus. they proposed to explain the missing mass that had been noticed in the atoms. these neutrons must have no charge and the same mass as a proton
• charges of subatomic particles

  • proton - +1
  • neutron - 0
  • electron - -1
• atomic number


  the number of protons in each atom of an element
• mass number


  the number of protons + the number of neutrons in the nucleus
• number of neutrons = mass number - atomic number
• ion


  when an atom loses or gains an electron
• isotopes 


  atoms of the same element with different number of neutrons, they have identical chemical properties but their physical properties, such as density, can differ
• noble gases

  the elements in group 0, they are very unreactive. their atoms have a very stable arrangement of electrons, 8 in the outer shell (except of helium which has 2)