Atomic structure: Atomic structure: Physics: GCSE (9:1)

• Structure of an atom

  a positively charged nucleus composed of protons and neutrons surrounded by electrons

  
• Average radius of an atom

  1 × 10^(-10) metres (0.0000000001 m)

  
• Average radius of a nucleus

  1 × 10^(-14) m which is about 10,000 times smaller than an atom

  
• Proton

  A positively charged particle found in the nucleus of an atom

  
• Neutron

  A neutral particle found in the nucleus of an atom

  
• Electron

  A negatively charged particle found in electron shells, orbiting the nucleus of an atom

  
• Relative mass of a proton

  1

  
• Relative mass of a neutron

  1

  
• Relative mass of an electron

  Approx. 1/2000

  
• Relative charge of a proton

  +1

  
• Relative charge of a neutron

  0

  
• Relative charge of an electron

  –1

  
• Ion

  An atom (or molecule) with an overall electric charge due to losing or gaining one or more electrons

  
• Positively charged ion


  An atom (or molecule) that has lost one or more electron

  
• Negatively charged ion


  An atom (or molecule) that has gained one or more electron

  
• Reason why atoms have no overall charge

  The number of electrons is equal to the number of protons so their charges cancel out

  
• Atomic (proton) number


  The number of protons in the nucleus of an atom

  
• Mass (nucleon) number


  The total number of protons and neutrons in the nucleus of an atom

  
• Isotope


  An atom with the same number of protons and a different number of neutrons