Atomic Structure

• Electron structure

  Electrons have fixed positions in atoms called shells or energy levels
• Filling electron shells

  1. Electrons fill an atom's shells in order of increasing energy

  2. The closer a shell is to the nucleus, the lower its energy level, so the first shell that is filled is the closest to the nucleus

  
• Electron shells

  • The innershell (closest to the nucleus) can have a maximum of 2 electrons
  • The next two shells can have a maximum of 8 electrons
  • Any extra electrons are then put into a fourth shell

  
• Periodic Table

  An ordered arrangement of all 118 known elements

  
• Periodic Table

  • Elements are arranged in order of their atomic number (number of protons)
  • Every time you move an element to the right, the proton number increases by 1
• Periods

  The rows of the periodic table
• The table is 'periodic' because elements with similar properties occur at regular intervals, i.e. periodically

  
• Groups

  • Columns of the periodic table
  • Elements in the same column have the same number of electrons in their outer shell (the highest energy level)
  • The group number equals the number of electrons an atom of that element has in its outer shell
• Because all elements in a column have the same number of electrons in their outer shell, they have similar chemical properties
• History of the Periodic Table

  1. Before scientists discovered sub-atomic particles (protons, neutrons and electrons), they tried to sort elements by their weight

  2. Today, we rank elements by their atomic number (the number of protons in an atom's nucleus)
• Newlands' periodic table

  • John Newlands was the first chemist to devise a periodic table
  • His periodic table was ordered by the weight of the element
  • The table was incomplete, and some elements were placed in inappropriate groups
• Mendeleev's periodic table

  • Dimitri Mendeleev realised that there may be undiscovered elements
  • He added gaps to Newlands' table to account for undiscovered elements
  • He even predicted the properties and masses of these undiscovered elements
• Everything whether it's living, non-living or even a cell itself is made up of lots of tiny particles which we call atoms
• Atom

  Basic structure is a central nucleus surrounded by electrons which orbit around the nucleus in rings that we call shells
• Particles that make up the nucleus

  • Protons
  • Neutrons
• Protons and neutrons

  • Have the same mass, with a relative mass of 1
  • Protons have a positive charge of 1+
  • Neutrons have no charge (are neutral)
• Electrons

  • Have a mass 2000 times smaller than protons and neutrons
  • Have a negative charge of 1-
• The size of an atom depends on which element it is
• Atoms have a radius of around 0.1 nanometers
• Ion

  An atom that has lost or gained electrons, so the positive and negative charges no longer balance
• Atomic number

  Tells us how many protons the atoms of that element have
• Mass number

  Tells us the total number of neutrons and protons in that atom
• The number of protons and electrons in an atom is always the same
• Atom

  Central nucleus comprising protons and neutrons, with electrons orbiting the nucleus
• Protons

  Determine which element the atom is
• Elements

  • Around 100 different elements
• Periodic table

  Organizes elements, each box represents a different element
• Isotopes

  Different forms of the same element that have the same number of protons but different numbers of neutrons
• Relative atomic mass

  The average mass of all the isotopes that make up a particular element
• Calculating relative atomic mass

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