Atomic structure

• Dalton's model

  Atom as a solid sphere that could not be divided into smaller parts, did not include protons, neutrons, or electrons
• Plum pudding model

  Cloud of positive charge, with negative electrons embedded in it. Protons and neutrons had not yet been discovered.
• Alpha scattering experiment

  1. Scientists fired alpha particles at gold foil

  2. They expected the alpha particles to travel straight through

  3. Some alpha particles bounced back and were deflected

  4. To explain this, scientists suggested the positive charge and mass of an atom must be concentrated in a small space at its centre, called the nucleus
• Nuclear model

  Electrons orbit the nucleus, but not at set distances
• The atom has a radius of 1x10^-10 m. Nuclei are around 10,000 times smaller than atoms and have a radius of around 1×10^-14 m.
• Electron shell (Bohr) model

  Electrons must orbit the nucleus at fixed distances, called shells or energy levels
• Relative mass

  Protons and neutrons have the same mass, given a relative mass of 1. Electrons have a very small relative mass of almost 0.
• Proton

  Smaller particle in the nucleus with an opposite charge to an electron
• Neutron

  Particle in the nucleus with no charge
• The Periodic Table lists over 100 types of atoms that differ in the number of protons, neutrons, and electrons they each have
• Atom

  Atoms of an element have equal numbers of protons and electrons, meaning they have no overall charge
• Electrons in an atom

  Placed in fixed shells, up to 2 in the first shell, 8 in the second and third shells
• Elements

  Substances made of one type of atom, each atom has the same number of protons
• Compounds

  Made of different types of atoms chemically bonded together, atoms have different numbers of protons
• Isotopes

  Atoms of the same element with different numbers of neutrons, giving them a different overall mass number
• Relative atomic mass

  The average mass of all the atoms of an element, taking into account the abundance of different isotopes
• Mixture

  Two or more elements or compounds that are not chemically combined together, can be separated using physical processes
• Separation techniques

  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Paper chromatography
• The modern Periodic Table lists approximately 100 elements
• First lists of elements

  • Ordered by atomic mass, had gaps for undiscovered elements, elements not clearly grouped by properties
• Mendeleev's Periodic Table

  • Ordered by atomic mass, had gaps for undiscovered elements, elements grouped by chemical properties
• Modern Periodic Table

  • Ordered by atomic number, no gaps, elements grouped by the number of electrons in the outer shell
• The discovery of electrons, protons, and neutrons led to improvements in the Periodic Table
• Group 0 (noble gases)


  Full outer shells, very unreactive, exist as single atoms, boiling points increase down the group
• Group 1 (alkali metals)


  One electron in outer shell, very reactive, reactivity decreases down the group as atoms get larger
• Group 7 (halogens)


  Exist as molecules made up of pairs of atoms, reactivity decreases down the group as atoms get larger
• Group 7 displacement


  More reactive Group 7 elements can take the place of less reactive ones in a compound