C1 Atomic Structure and the Periodic Table

• Atoms


  The smallest part of an element that can exist
• Chemical symbols

  Represent an atom of an element e.g. Na represents an atom of sodium
• Compounds

  Formed from elements by chemical reactions, contain two or more elements chemically combined in fixed proportions, can be represented by formulae
• Mixtures

  Consist of two or more elements or compounds not chemically combined together, can be separated by physical processes
• Development of the model of the atom

  1. First thought to be tiny spheres that could not be divided

  2. Discovery of electron led to plum pudding model

  3. Alpha particle scattering experiment led to conclusion mass concentrated in nucleus

  4. Bohr suggested electrons orbit nucleus at specific distances

  5. Later experiments showed positive charge of nucleus could be subdivided into protons

  6. Chadwick's work provided evidence for existence of neutrons
• Atomic number

  The number of protons in an atom of an element, all atoms of a particular element have the same number of protons
• Atoms have an overall charge of 0, so number of protons = number of electrons
• Relative mass of subatomic particles

  Proton = 1, Neutron = 1, Electron = very small
• Mass number

  The sum of the protons and neutrons in an atom
• Isotopes

  Atoms of the same element with different numbers of neutrons
• Relative atomic mass

  An average value that takes account of the abundance of the isotopes of the element
• Electronic structure

  Electrons occupy the lowest available energy levels (shells closest to nucleus), can be represented as 2,8,1 for sodium

  
• Atom


  The smallest part of an element that can exist
• Element

  A substance of only one type of atom
• There are approximately 100 elements listed in the periodic table
• Groups of elements based on properties

  • Metals
  • Non-metals
• Compounds have different properties than their constituent elements
• Mixture

  Two or more elements or compounds not chemically combined together
• Methods to separate mixtures

  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Chromatography
• Separation methods for mixtures do not involve chemical reactions
• Simple distillation

  1. Liquid boils off and condenses in the condenser

  2. Thermometer reads the boiling point of the pure liquid
• Crystallisation/Evaporation

  1. Solution is heated until all the solvent evaporates

  2. Solids stay in the vessel

  3. Saturated solution is cooled to form crystals
• Fractional distillation

  1. Mixture is repeatedly condensed and vaporised in a fractionating column

  2. Liquids condense at different heights in the column
• Filtration

  1. Insoluble solid (residue) gets caught in the filter paper

  2. Filtrate is the substance that comes through the filter paper
• Chromatography

  1. Mixture is dissolved in a solvent and placed on paper

  2. Solvent rises up the paper, separating the mixture
• Separating funnel

  Apparatus for separating immiscible liquids of different densities
• Plum-pudding model

  Atom is a ball of positive charge with negative electrons embedded in it
• Bohr/nuclear model

  Electrons orbit the nucleus at specific distances (shells), came from alpha scattering experiments
• Later experiments led to the discovery of protons in the nucleus
• James Chadwick's work provided evidence for the existence of neutrons in the nucleus
• Atom structure

  Small central nucleus (protons and neutrons) with electrons orbiting
• Masses: proton 1, neutron 1, electron very small; Charges: proton 1, neutron 0, electron -1
• Atoms are electrically neutral because they have the same number of electrons and protons
• Radius of an atom is 0.1 nm
• Radius of a nucleus is 1 x 10-14 m, which is 1/10000 of the atom radius
• Number of protons in the nucleus

  Atomic number
• Atoms are electrically neutral


  They have the same number of electrons and protons
• Radius of an atom

  0.1 nm
• Radius of a nucleus

  1 x 10-14 m
• Atoms of the same element have the same number of protons in the nucleus