Structure of an Atom

• Size of an atom

  • Atoms are very small 
  • They have a radius of 1 x 10⁻¹⁰ metres 
  • This is an approximate figure as some atoms are larger than others
• The Nucleus

  • Atoms contain a central region , that is positively charged called the nucleus 
  • The nucleus of the atom contains most of the mass 
  • The radius of the nucleus is less than 1/10000 of the radius of the atom
• What is inside of an atom

  • The nucleus contains protons , which have a positive charge 
  • The nucleus is also made up neutrons which have got no charge (neutral) 
  • This means that the nucleus has an overall positive charge (due to the protons) 
  • The nucleus is surrounded by electrons , which have a negative charge

  
• Numerical charges of Protons , Neutrons and Electrons

  • Protons have an electrical charge of +1 
  • Neutrons have an electrical charge of 0 
  • Electrons have an electrical charge of -1
• Charges of atoms

  • Atoms have equal numbers of protons and electrons 
  • This means that they have no overall charge

  
• Energy levels

  • Electrons are arranged in different distances from the nucleus  
  • These are energy levels

  
• Higher and Lower energy levels

  • Energy levels which are further from the nucleus are at a higher energy 
  • Energy levels which are closer to the nucleus are at a lower energy

  
• What moves electrons to a higher energy level

  • Electrons can change energy levels if they gain or lose energy 
  • If the atom absorbs electromagnetic radiation (e.g. light) it can move to a higher energy level

  
• What moves electrons to a lower energy level

  • Electrons can change energy levels if they gain or lose energy 
  • The atom can emit electromagnetic energy and the electron returns back to a lower energy level

  
• What gets emitted when an atom drops an energy level?

  Electromagnetic radiation
• An atom that loses one of its outer electrons becomes a positive ion

  
• An atom that gains an electron becomes a negative ion