atomic structure

• Everything whether it's living, non-living or even a cell itself is made up of lots of tiny particles which we call atoms
• A single cell probably contains more than 100 trillion atoms
• Atom structure


  • Central nucleus surrounded by electrons which orbit around the nucleus in rings that we call shells
• Protons


  Particles in the nucleus, have a positive charge
• Neutrons


  Particles in the nucleus, have no charge
• Electrons


  Particles orbiting the nucleus, have a negative charge
• Protons and neutrons have the same mass, with a relative mass of 1
• Electrons have a mass 2000 times smaller than protons and neutrons
• The size of an atom depends on which element it is, generally around 0.1 nanometers in radius
• Most of an atom is empty space, like the solar system with a central nucleus and orbiting electrons
• The nucleus is 10,000 times smaller than the width of the atom
• The number of protons and electrons in an atom is equal, making the atom overall neutral
• Ion


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


  • One minus negative ion
  • Two minus negative ion
  • One plus positive ion
• Periodic table


  Each box represents a different type of atom, called an element
• Elemental symbol


  One or two letter symbol that represents an element
• Atomic number


  Number of protons in the atom, determines the element
• Mass number


  Total number of neutrons and protons in the atom
• The number of protons and electrons in an atom is always the same
• The first major theory that had tried to explain what stuff is made out of was atomic theory
• Atomic theory


  The idea that everything is made up from tiny little particles that can't be broken down any further and that they're separated from each other by empty space
• Democritus proposed atomic theory

  Around 500 BC
• When atomic theory was improved upon

  1800s
• John Dalton's atomic model


  Atoms as solid spheres, different types of spheres make up different elements
• J.J. Thompson proposed the plum pudding model


  1897
• Plum pudding model


  • Atoms contain negatively charged particles (electrons)
  • Atoms have a general ball of positive charge with discrete electrons stuck in it
• Rutherford and students made a big discovery


  1909
• Rutherford's experiment


  1. Fired positively charged alpha particles at a thin sheet of gold

  2. Some alpha particles were deflected to the side or back, proving the plum pudding model wrong
• Rutherford's nuclear model


  Atoms have a compact nucleus containing all the positive charge, with a cloud of negative charge around it
• Rutherford's nuclear model had a flaw - the negative electrons should collapse into the positive nucleus
• Niels Bohr suggested a solution

  1913
• Bohr's model


  Electrons orbit the nucleus in shells, preventing the atom from collapsing
• Further experiments by Rutherford found the positive charge in the nucleus is made up of protons
• James Chadwick provided evidence for neutral particles (neutrons) in the nucleus
• The current understanding of the atom is based on Bohr's model with a few small changes
• Atom


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


  Determine which element the atom is
• Hydrogen


  • Smallest element, with 1 proton and 1 electron
• There are around 100 different elements
• Periodic table


  Organizes elements, each box represents a different element