C1

• Atom


  Smallest part of an element that can exist
• Chemical symbol


  Represents an atom of an element
• Elements


  • Substances with only one type of atom
  • Listed in the periodic table
  • About 100 different elements
• Elements


  • Can be classified as metal or non-metal depending on their properties
  • The columns in the periodic table are called groups and contain similar elements
  • The rows in the periodic table are called periods, elements show a gradual change in properties across a period
• Compound


  Made from two or more different elements (types of atoms) combined together in fixed proportions
• Compounds have different properties from the elements they are made from
• Compounds can only be separated into elements by chemical reactions
• Mixture


  Two or more elements or compounds not chemically combined together
• The chemical properties of each substance in a mixture are unchanged
• Separating techniques


  • Filtration
  • Crystallisation/Evaporation
  • Simple distillation
  • Fractional distillation
  • Chromatography

  
• Simple distillation


  1. Liquid boils off and condenses in the condenser

  2. The thermometer will read the boiling point of the pure liquid

  
• Crystallisation/Evaporation


  1. Evaporating to separate a soluble solid from a (non-flammable) liquid

  2. To create hydrated salt crystals do not evaporate all the water from the mixture
• Filtration


  1. The insoluble solid (called residue) gets caught in the filter paper

  2. The filtrate is the substance that comes through the filter paper
• Fractional distillation


  1. The liquid with the lower boiling point forms the greatest percentage of vapour

  2. The vapour mixture condenses and evaporates as it moves up the fractionating column

  3. The liquid with the lowest boiling point will be the first 'fraction' to collect
• Before the discovery of the electron atoms were thought to be tiny spheres that could not be divided
• Plum-pudding model


  The atom was a ball of positive charge with negative electrons embedded in it
• Rutherford and Marsden's alpha scattering experiments


  • Showed that all the mass of the atom was in the nucleus
  • Showed that all the positive charge of the atom was in the nucleus
• Nuclear model


  • The centre of the atom was called the nucleus
  • Electrons were thought to orbit the nucleus, like planets around the sun
• Bohr model


  • Electrons orbit the nucleus at specific distances
  • Electrons are on energy levels or shells
• Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name proton was given to these particles.
• The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus.
• Atom


  Small central nucleus made up of protons and neutrons around which there are electrons
• Subatomic particles


  • Proton
  • Neutron
  • Electron
• In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
• Atomic number


  The number of protons in an atom
• Mass number


  The total number of protons and neutrons in an atom
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Isotopes of an element have the same chemical properties because they have the same electronic structure
• Relative atomic mass


  An average value that takes account of the abundance of the isotopes of an element
• Calculating relative atomic mass

  R.A.M = (isotopic mass x % abundance) / 100
• Energy levels


  Electrons occupy particular energy levels in an atom
• The electrons in an atom occupy the lowest available energy levels
• Group

  Columns in the periodic table containing similar elements
• Period


  Rows in the periodic table
• Elements in the same group in the periodic table have the same number of electrons in their highest energy levels (outer electrons) and this gives them similar properties
• Noble gases


  Elements in Group 0 of the periodic table, unreactive because their atoms have stable arrangements of electrons
• Modern periodic table


  • Arranged in order of atomic (proton) number
  • Elements with similar properties are in columns, known as groups
  • Can be seen as an arrangement of the elements in terms of their electronic structures
• Mendeleev overcame some problems with early periodic tables by leaving gaps for elements that had not been discovered and in some places changing the order based on atomic weights
• Metals


  Elements that react to form positive ions
• Non-metals


  Elements that do not form positive ions